Adriano Baratè Goffredo

Haus Luca

A Ludovico
email: ludovico@dico.unimi.it

A Ludovico An

AN XML-BASED FORMAT FOR ADVANCED MUSIC FRUITION

établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Specific encoding formats to represent music features are already commonly accepted and used. They are aimed at a precise characterization of different music aspects. For example, AAC, MP3 and PCM formats encode audio recordings; MIDI represents a well known standard for computer-driven performance; JPEG and TIFF files can contain the results of a scanning process of scores; Finale, NIFF and Sibelius formats are aimed at score typing and publishing, and so on. But such formats are often characterized by an intrinsic limitation: they can describe music data or metadata for score, audio tracks, computer performances of music pieces, but they seldom encode all these aspects together.

On the contrary, we are interested in a "comprehensive" representation and fruition of music, addressed to musicologists, performers, students and people simply interested in music. The key characteristics that a comprehensive format should support can be summarized as follows:

• Richness in the multimedia descriptions related to the same music piece (graphical, audio, and video contents). • Possibility to link and perform a number of media objects of the same type (for instance, many performances of the same piece or many score scans coming from different editions). • Complete synchronization among time-based contents, meaning that audio and video contents are kept synchronized with score advancing, even when the user switches from a particular performance to another, or from a particular score edition to another.

• Interaction, that is the possibility for the users to click any point of the score and jump there also in the audio content currently performed, as well as the possibility to navigate the audio track moving the related slider control and highlighting the related portion of score. Achieving these goals imply: 1) designing and adopting a suitable format to represent music, 2) implementing software applications to achieve synchronization and user interaction, and 3) encoding music pieces and all the related material in the aforementioned format. These subjects will be now treated in greater detail.

A COMPREHENSIVE DESCRIPTION OF MUSIC

In our opinion, it is necessary to conceive music description in a comprehensive way. In order to appreciate the richness of music communication, let us recall that such language is made up of many different and complementary aspects: music can be (and actually is) the idea that the composer translates to symbols as well as their performance, the printed score that musicians read as well as a number of other related contents. A complete analysis of music richness and complexity is provided in [START_REF] Haus | A Multi-Layered Time-Based Music Description Approach based on XML[END_REF], where six different levels of music description are identified -namely General, Structural, Logical, Notational, Audio, and Performance layers. This multilayer structure, suitable for our concept of comprehensive description of music, is reflected by the encoding format we are developing at LIM.1 Our goal is providing a highly integrated performance of music, where score, audio, video, and related graphical contents can be enjoyed together. Nowadays we dispose of good and commonly accepted file formats to describe only one aspect (sometimes a few aspects) of music, but experts and technicians are more and more interested in ways to integrate different information sources and representation methods.

What does the adjective comprehensive mean, when applied to music field? Music language is made up of many different and complementary aspects. One of the most complete analyses of music richness and complexity is provided in [START_REF] Haus | Recommended Practice for the Definition of a Commonly Acceptable Musical Application Using the XML Language[END_REF], where six different levels of description are identified: namely general, structural, logical, notational, audio and performance layers. This multi-layer structure could answer the request of completeness in the "horizontal dimension", as the layers we listed can be considered a good coverage of the different domains of music. They take into account the evidence that music is the composition itself as well as the sound a listener hears, and is the score that a performer reads as well as the execution provided by a computer system. In order to appreciate the richness of such a kind of communication, we can point out that music -in its most general meaning -can stimulate different senses: the sense of hearing, the sense of sight and even the sense of touch. In this sense, music is multimedia (as several different media are employed to convey information) and multi-layered (as information can be structured according to a multi-layered layout).

After identifying in general terms the layers music language can be divided in, we should face the problem of describing each of them in a comprehensive way.

We have listed the elements that can constitute the horizontal dimension; now let us move down the vertical dimension of the overall context.

Any layer presents different characteristics and requires a specific analysis of its peculiarities. As an example, we can consider the logical layer, where music events are listed and organised. It should provide a logical representation of the piece, made of clefs, time and key signatures, bars, notes, rests, horizontal symbols such as hairpins, and so on… The problems involved here mainly deal with music grammar and notation capabilities: a comprehensive format should support virtually all the different symbols, in all their versions, taken from any notation style. Even a small and welldefined subset of the whole problem is difficult to solve. In fact, considering only the Common Western Notation, it is rich in unusual notations such as the symbol named coulé,2 nowadays almost disappeared from Music Theory texts. We have cited a form of embellishment, as many forms of ornament (in their name, graphical representation, and musical resolution) are related to a particular period, style and even author. Nevertheless, music grammar presents many other examples of variety in notation. As a matter of fact, we cannot oppose this phenomenon, which has historical justifications and represents an aspect of richness; we simply have to take it into account.

Leaving the "reassuring" field of Common Western Notation, and considering for instance contemporary scores, the problem of a comprehensive encoding format becomes hard to solve. And, even assuming that we are able to support all the symbols derived from the past and the present scores, what about future? Who could forecast the evolution of musical notation? Even bestselling notation software applications show serious gaps when they have to represent contemporary music or pieces beyond Common Western Notation.

In other words, it is not possible to identify all the instances of music symbols, from any language, notation style, historical period and geographical region. Probably, this is the reason why Perry Roland in [4] rejects the SMDL standard, saying that "it defines the term music much too broadly to effect a practical solution". However, from our perspective, a general definition of the concept of music is desirable.

Till now we focused on only one layer of music communication, but other description levels are affected by similar problems. For instance, despite its apparent simplicity, the general layer (devoted to metadata such as the author, the title, and the genre of the coded music work) hides challenging and insidious problems: Which is the comprehensive information a user expects to find in this section? Is it possible to treat the general metadata for a classical work like the ones for a rock or pop piece? Is it possible to create taxonomy about music genres? These are only some of the questions we should answer when we choose or design an encoding format for music. A general idea, present both in IEEE and in ISO/IEC recent approaches to music description, is taking advantage of existing formats. As a consequence, the problem of a comprehensive representation for music can be articulated as follows.

• Which already existent descriptions should be supported? • How to code the data and metadata that are not present in other kind of representation? • How to combine such heterogeneous information within an integrated description framework? • How to provide interoperability and synchronization in the multi-layer environment? The following section will answer these questions.

MX FORMAT FOR MUSIC REPRESENTATION

In order to integrate all the aspects of music within a single description, we are developing a new XML-based format, called MX. Currently, MX is undergoing the IEEE standardization process (IEEE PAR1599), as described in [START_REF] Haus | A Multi-Layered Time-Based Music Description Approach based on XML[END_REF]. Our approach is different from other kinds of music encodings, in particular because we represent music information according to a multi-layer structure and to the concept of space-time construct. Now we will explain these key concepts in greater detail.

The first key feature of MX format is the multi-layer structure. We can conceive each layer as a different degree of abstraction in music information. For a common and exhaustive description, in MX we distinguish the Structural, Music Logic, Notational, Performance and Audio layers. This multi-layered description allows MX to support a number of different formats aimed at music encoding without modifying such commonly accepted standards. For example, MusicXML can be integrated in our format to describe score symbolic information (e.g., notes and rests), whereas other common file types such as JPEG and TIFF for notational layer, MP3 and WAV for audio layer can be linked to represent other facets of music.

The second peculiarity of the MX format, directly related to its multi-layered structure, is the presence of a space-time construct called spine. In fact, considering music as a multi-layered information, we need a means to link and synchronize the heterogeneous facets that compose such information. To this end, we introduced the concept of spine, namely a structure that relates time and spatial information (see Figure 1). The light grey lines graphically represent the synchronization among different layers provided by the spine. In the example, three representations of the same piece are present: a score in TIFF format, a MIDI file and an audio track. Events are univocally identified by id attributes inside the spine structure. Each layer containing music data refers to the event identifiers listed in the spine, and this provides a global internal synchronization. Of course, some data intrinsically cannot be synchronized: it is the case of general metadata or related graphical files (photos, sketches, pictures) which have no relationships towards score representation and performance.

Through spine mapping, it is possible -for example - to fix a point in a layer instance (e.g. the notational one) and jump to the corresponding point in another one (e.g. the audio one). Besides, if many media objects of the same type are provided, a real-time switch from an object to another is allowed.

MX LAYERS

After presenting the multi-layered structure of MX and the time-space construct that allows synchronization, let us briefly describe the meaning and the contents of each MX layer.

The Logic layer contains information referenced by all other layers, and it represents what the composer intended to put in the piece. It is composed of two elements: i) the Spine description, used to mark the significant events in order to reference them from the other layers and ii) the LOS (Logically Organized Symbols) element, that describes the score from a symbolic point of view (e.g., chords, rest).

The Structural layer contains explicit descriptions of music objects together with their causal relationships, from both the compositional and the musicological point of view. It represents how music objects can be described as a transformation of previously described music objects.

The Notational layer links all possible visual instances of a music piece. Representations can be grouped in two types: notational and graphical. A notational instance is often in a binary format, such as NIFF or Enigma, whereas a graphical instance contains images representing the score. Usually, the latter is in a binary format too (e.g., a JPEG image or a PDF file), but it can also be a vector image. The information contained in this layer is tied to the spatial part of the Spine structure, allowing its localization.

The Performance layer lies between notational and audio layers. File formats grouped in this level encode parameters of notes to be played and parameters of sounds to be created by a computer performance. This layer supports symbolic formats such as MIDI, Csound or SASL/SAOL files.

Finally, the Audio layer describes properties of the source material containing music audio information. It is the lowest level of the layered structure. The complete DTD of MX 1.5 format is available at http://www.lim.dico.unimi.it/mx/mx.zip, together with a complete example of music representation in MX format.

PREPARING AN MX FILE

As stated before, MX format allows a very rich and comprehensive description of music contents. Of course, richness is just a possibility: a piece could be described only in terms of its music symbols, without multimedia objects attached, and the MX file would be validated in any case. However, we are interested in a comprehensive description of music, so we will analyze the problems involved in the process of creation of a complex file.An MX file, like any other XML-based encoding, can be written and edited even by a simple text editor. It is virtually possible to encode all the score symbols and all the synchronization information by hand and in text format. Nevertheless, this approach would be very difficult and time-consuming.

First, for a musician the task of writing notes and rests according to XML formal rules (that are substantially different from score notation) is unacceptable. Besides, after obtaining a well-formed, valid, complete and semantically correct encoding of the piece, the author of the MX file should face other difficult tasks: e.g., manually finding values to map and synchronize heterogeneous media objects and entering those values in the MX file. This is the main reason why we implemented a number of utilities to support the creation and management of rich MX files.

MX UTILITIES

In order to simplify the assemblage process of heterogeneous contents within a single music description, we developed a suite of software applications. Unfortunately, the process required to map and synchronize heterogeneous media at the moment cannot be performed automatically. This would require, for instance, a good OMR3 system in order to recognize musical symbols in scores, even when autographical. Besides, such symbols should be automatically put in relationship with the spine structure. As regards audio information, an effective application to extract automatically music events from a complex audio track should be employed. Some well known limits in automated music analysis techniques prevented us from reaching this ambitious goal.

On the other hand, acquiring music events by a completely hand-made process would be a terrible waste of time and energy: it would require, for instance, an accurate listening of the audio tracks in a sound editing environment, or the precise computation of the "bounding box" around each music event in a digital imaging software. Calculating milliseconds and pixels by hand is not effective nor efficient.

Our solution was designing and implementing some aiding applications to speed up the mapping process. In particular, two applications were released and employed to feed up MX Navigator with a rich MX file: MX Graphic Mapper and MX Audio Mapper.

MX Graphic Mapper is the application devoted to link the logic events of a MX file to their corresponding graphic counterparts within the score image (see Figure 2). A MX file is opened, scanned and a list of all notes/rests events is created. The user opens one or more images that contain the score and begins mapping all the events by drawing rectangles in the central window. The representation of the note/rest event is graphically shown in the "Event Graphic Parser" and the XML fragment to be added is visible in the upper part of the interface. When a rectangle is created, the application generates the XML line by reading the current event in the "Spine Elements" listbox, and by computing the coordinates of the rectangle. When a new line is added, the current element indicator is moved forward and the mapping process continues.

The MX Audio Mapper is the application used to compute the indexes of events in audio/video clips (see Figure 3). This application is similar to the previous one, but instead of mapping the graphic representations of a piece (scores) it maps its audio/video performances (clips). To map a clip, the MX and the audio/video file are opened, and some parameters are defined: the timing unit per quarter used in the logic layer and the rhythm figure to be processed (quarter, quaver …). The mapping process is achieved by "tapping" the rhythm on a button: when this process is completed, the MX spine is processed and all the timings of the events are computed (in seconds), interpolating figures between two consecutive "taps". After this preliminary procedure, the computed maps can be fine-tuned by hearing the selected map position in the clip, and by adjusting the wrong timings.

As a consequence, our way to compile an MX file is not completely automated nor completely hand-made: it is a compromise that could be defined as a "semiautomated solution", as human intervention is still fundamental, but computer plays an important role.

MX NAVIGATOR

MX Navigator is the name of the application that allows an integrated and evolved navigation of music contents. It presents all the aspects we cited before: richness in multimedia description of music, synchronization among heterogeneous contents and easy user interaction.

MX Navigator was installed at the exhibition "Tema con Variazioni. Apart from a number of multimedia objects such as greeting cards, playbills, historical photos and sketches, the software mainly shows two versions of the score (an autographical and a printed one), a video and two audio performances of Puccini's aria.

The central part of the interface contains the score, since this is the main media in terms of interaction and even because of its visual extent.

The upper left part of the window contains controls related to audio/video interaction. In this application there are three different clips: an audio clip of a 1953 version performed by the Italian tenor Di Stefano and both an audio and video clip of the 1984 version performed by Aragall at the Verona's Arena. When a version is chosen and played, the music and/or video is executed, and in the score window a red rectangle indicates the event being played by the clip (thanks to the synchronization achieved by the MX Audio Mapper and the MX Graphic Mapper). Since there are many parts in the score (all coded into the MX file), it must be possible to select the current part to follow. This application is intended to be used even by nonmusicians, so this choice is simplified, and only two parts can be selected. To do this in the top of the interface there are two buttons that control which part is to be followed by the rectangle in the score, the Clarinetto or the Tenor (Cavaradossi) one.

In the top of the interface, the controls are devoted to manage the score visualization. In this MX file there are two types of mapped scores: the autographical Puccini version and the Ricordi published version. The upper left buttons switch (even when running an audio/video clip) between this two scores. The upper right buttons control the zoom (50% or 100%) and the current page displayed (only in the Pause state, otherwise the current page is automatically selected to follow the audio/video clip execution).

The left bottom part of the interface is simply used to open many graphical elements related to the piece.

This visual interface allows a number of different ways to enjoy music. First, it is possible to select a score version, an audio track, a leading instrument and simply follow the instrument part evolution. This is a first original degree in music fruition, as music can be listened and watched in a synchronized fashion. But a second way to enjoy music through MX Navigator is even more interesting: it consists in switching from an aural/visual representation to another. In other words, it is possible to compare in real time different versions of the score (the hand-made and the printed one) or different performances. When the user decides to switch from a representation to another, MX Navigator continues from the point previously reached. Finally, the application suggests a third way to enjoy music, that consists in altering the original sequence of music events. It is possible to jump -forward or back -from a point to another point of the score, both in its visual and aural representations; of course, the effect will be the same as the former and the latter are synchronized.

CONCLUDING REMARKS

The MX Navigator version we presented at the exhibition "Tema con Variazioni" is an interface conceived for the spread of art and music among people not necessarily cultured. The application is characterized by a comprehensive multimedia description of music, synchronization among heterogeneous contents and easy user interaction.

Since our tool is working on XML data, a possible future application will be to have it as a client-side script of a standard browser.

We think that MX Navigator represents an important experiment in the field of cultural heritages, as users can enjoy music also in non-traditional ways and they can intuitively interact with musical contents.

Figure 1 .

 1 Figure 1. Synchronization among Notational, Performance and Audio layer provided by spine.

Figure 2 .

 2 Figure 2. Screenshot of the MX Graphic Mapper application.

  Musica e innovazione tecnologica'' [Theme with variations. Music and technological innovation], a voyage into the Italian musical heritage through the rooms of Rome's Music Park Auditorium. One of the purposes of the exhibition was making music tangible and visible bringing together the five senses, not just hearing. In this context we have designed a simple user interface, conceived for not cultured people, in order to listen to and visualize a track alongside variously interpreted scores. MX Navigator represents the natural evolution of MX Demo [1], an experimental prototype presented in a scientific research context at AXMEDIS 2005 conference. The main differences between MX Demo and MX Navigator are two: • The latter is a generalized version of the former, as MX Demo was designed only to demonstrate MX format possibilities and worked on the limited number of pieces consequently chosen, whereas MX Navigator is virtually able to open any MX file. It is able to adapt itself in real time to the different kind and number of media contained. • MX Navigator is necessarily characterized by animproved usability and by a simpler user interface. In fact, MX Demo had to be presented to a scientific audience by its authors, while MX Navigator is at common users' disposal in a public exhibition. MX Navigator allows an integrated fruition of different media contents related to the same music piece. For the exhibition held in Rome, we translated into MX the aria "E lucevan le stelle…" from Puccini's Tosca -III Act. The choice of that piece was imposed by the leitmotiv of the exhibition "Tema con Variazioni", nevertheless MX Navigator could open and play any MX file.

Figure 3 .

 3 Figure 3. Screenshot of the MX Audio Mapper application.

Laboratorio di Informatica Musicale, Dipartimento di Informatica e Comunicazione, Università degli Studi di Milano.

Coulé is a passing appoggiatura, namely a grace note that softens the line making it smoother by binding the notes together. This embellishment was a convention in both the XVII and XVIII centuries, often employed by W.A. Mozart himself.

OMR stands for Optical Music Recognition.

ACKNOWLEDGMENTS

The authors want to acknowledge researchers and graduate students at LIM, and the members of the IEEE Standards Association Working Group on Music Application of XML (PAR1599) for their cooperation and efforts. Special acknowledgments are due to: Denis Baggi for his invaluable work as working group chair of the IEEE Standard Association WG on MX (PAR1599); Maria Pia Ferraris and Cristiano Ostinelli (Ricordi) for their fundamental contributions as regards the original material (autographic and printed scores, sketches, pictures, photos) used in MX Navigator.


Leigh Vanhandel

TRENDS IN/OVER TIME: RHYTHM IN SPEECH AND MUSICAL MELODY IN 19 TH -CENTURY ART SONG

This paper presents the results of a quantitative study of the relationship between rhythmic characteristics of spoken German and French and the rhythm of musical melody in 19 th -century art song. The study used a modified version of the Normalized Pairwise Variability Index, or nPVI, to measure the amount of variability between successive rhythmic events in the melodies of over 600 songs by 19 French and German composers. The study returned an unexpected result; songs written to texts in the two languages exhibited sharply diverging trends as a function of time through the 19 th century. This trend is reflected both in the overall trends and in the trends of individual composers.

INTRODUCTION

Rhythm in spoken language is an effect involving the isochrony, or the regularity of occurrence, of some type of speech item; the item can be a speech unit (such as a syllable) or a linguistic event (such as accent or stress). Languages may be categorized as syllable-timed (for example, French and Spanish) or stress-timed (for example, English and German).

In a stress-timed language such as German, stressed syllables are perceived to occur regularly, resulting in an expansion or compression of individual syllables in order to accommodate the recurrence of the stresses. By contrast, in a syllable-timed language such as French, it is the individual syllables that are perceived to be of nearly equal duration and therefore occurring at regular time intervals.

The linguistic classifications of syllable-timed and stress-timed are controversial ones. Repeated attempts to empirically confirm isochrony between stresses or syllables have failed [START_REF] Beckman | Evidence for speech rhythms across languages[END_REF][START_REF] Laver | Principles of Phonetics[END_REF]. However, many linguists agree that the principle of isochrony can underlie the rhythm of a language even if it is not manifested in an experimentally demonstrable fashion [START_REF] Fox | Prosodic Features and Prosodic Structure: The Phonology of Suprasegmentals[END_REF]. The durational differences between stresses or syllables tend to be well below the threshold of perception, so even though the principle cannot be proven quantitatively, we still perceive the unit to be recurring isochronously. As a result, many linguists now regard isochrony as a primarily perceptual phenomenon, describing it as a "subjective" rather than "objective" isochrony. Some of the strongest evidence for the perceptualbased theory of linguistic isochrony comes from studies done on language acquisition and categorization in infants which demonstrate that infants are able to discriminate on the basis of rhythm between sentences in their native language and sentences from a language belonging to another rhythmic class [START_REF] Ramus | Correlates of linguistic rhythm in the speech signal[END_REF]. The perceptual processes involved in discriminating language on the basis of rhythm have also been found in tamarin monkeys and most recently, in rats [START_REF] Toro | Effects of backward speech and speaker variability in language discrimination by rats[END_REF].

Recent studies, most notably Grabe & Low [START_REF] Grabe | Durational variability in speech and the rhythm class hypothesis[END_REF] and Ramus et al. [START_REF] Ramus | Correlates of linguistic rhythm in the speech signal[END_REF], have demonstrated that there are quantitative rhythmic differences between languages historically considered to be stress-and syllable-timed languages. These studies have focused on measuring vowel duration in the two types of languages; they hypothesized that since vowels are primarily responsible for the length of a syllable, an increased variability in vowel length would result in greater variability in syllable length, whereas a language with little variation in vowel length would have little overall variation in syllable length. The model Grabe & Low [START_REF] Grabe | Durational variability in speech and the rhythm class hypothesis[END_REF] developed to measure the amount of durational variability in a language is called the normalized Pairwise Variability Index, or nPVI, defined as: [START_REF] Beckman | Evidence for speech rhythms across languages[END_REF] where m is the number of items and d is the duration of the kth item. Grabe and Low's research demonstrated that because stress-timed languages have greater durational variability between successive vocalic intervals due to compression and expansion of syllables, stress-timed languages will have a higher nPVI measurement than a syllable-timed language with lower variability.

APPLICATION TO MUSIC

Previous studies

While the nPVI was originally intended to be a measure of the average variation of successive vocalic intervals in spoken language, several studies have used the measure to study the relative durational contrast between successive rhythmic events in music. The following

! nPVI = 100" d k # d k+1 d k + d k+1 ( ) / 2 k =1 m #1 $ / m # 1 ( ) % & ' ' ( ) * *
sections summarize the methodology and results from previous studies.

Patel and Daniele (2003) [6]

Patel and Daniele [START_REF] Patel | An empirical comparison of rhythm in language and music[END_REF] used the nPVI measure to study fragments from British and French instrumental music. The musical material for Patel and Daniele's study was drawn from the Barlow and Morgenstern A Dictionary of Musical Themes, 2 nd Edition (1983), and focused on 19 th -20 th century composers 1 who were native speakers of British English and continental French. The themes were selected using very strict criteria, narrowing the number of themes eligible for the study to a total of 319 themes from six English and ten French composers.

Patel and Daniele's results indicated that the rhythm of instrumental music by British composers demonstrated a higher durational contrast than that of French composers, as expected based on the higher durational contrast in spoken British English than in spoken French.

Huron and Ollen (2003) [4]

Huron and Ollen [START_REF] Huron | Agogic contrast in French and English themes: Further support for Patel and Daniele (2003)[END_REF] replicated Patel and Daniele's study, dramatically expanding the sample size. Their results for English and French were consistent with those of Patel and Daniele, although the difference between the mean values was smaller than that found by Patel and Daniele; nonetheless, the results were significant, indicating the hypothesis holds up even with less stringent sampling criteria.

In addition to confirming Patel and Daniele's original hypothesis about British English and French, Huron and Ollen calculated average nPVI values for instrumental music written by composers of other nationalities (results reproduced in Table 1). They noted that results were comparable for related languages such as American English and British English, for Austrian and German, and for syllable-timed Romance languages such as French, Spanish, and Italian. 1 Their criterion was that the composer was born in the 19 th century and died in the 20 th .

Nationality

The current study

The previous studies focused on the rhythms of instrumental music. In fact, one study indicated they were studying instrumental music because they believed it a foregone conclusion that vocal music would reflect the rhythms of speech, saying: "[i]f music is based on words, and words have different rhythmic properties in the languages under study, then it would be no surprise if musical rhythm reflected linguistic rhythm." [START_REF] Patel | An empirical comparison of rhythm in language and music[END_REF] The current study modified the nPVI measure and applied this modified system to vocal music. A large database of musical information was created in David Huron's Humdrum Toolkit, an open source software package designed to assist with music research. The database consisted of the melodic, rhythmic, phrasing, and textual information from over six hundred 19 th century French and German art songs by nineteen composers, as shown in Table 2. Unlike the strict selection criteria of Patel and Daniele, the primary selection criteria in this study were that the composers had to be native speakers of the language, setting a text originally written in that language by a poet who was a native speaker of the language. 2Because of the different repertory and large size of the database, it was necessary to make some modifications to the method of calculating the nPVI. Rhythmic events such as rests and grace notes turned out to have a significant impact on the nPVI value. These were rhythmic events that were either avoided or modified in the previous studies; all of the previous studies discarded thematic incipits containing grace notes, and Patel and Daniele's study ignored the duration of rests, while Huron and Ollen added the duration of the rest to the previous duration.

French

The previous studies used as source material short melodic incipits, and as such did not have to include phrasing in their calculations. This study included full songs as source material, requiring the nPVI calculations to be modified to calculate the nPVI at the level of the musical phrase.

Calculating the nPVI at the level of the musical phrase coincides with linguistic research on isochrony. There is evidence that perceived isochrony is confined to relatively short speech fragments; that is, the duration of the perceived isochrony has a tendency to change from phrase to phrase and not remain constant over a longer utterance. In fact, linguistic isochrony seems to conform to the principles of the intonational phrase, defined as "the unit at which the cognition, physics, syntax, phonetics, and phonology of speech converge." [START_REF] Wennerstrom | The Music of Everyday Speech: Prosody and Discourse Analysis[END_REF] Because the nPVI measure is normalized, two phrases can exhibit the exact same nPVI but use different units of isochrony; this accounts for varying rates of speech across (and within) speakers. As a result, it is of limited use to calculate the nPVI of multiple phrases without regard for phrase boundaries, as each phrase will likely be using a different unit of isochrony. It is more fruitful and relevant to calculate the nPVI value of individual phrases.

When applying the nPVI to music, it follows that in order to accurately represent durational variability of rhythmic events, the nPVI measure should be applied to the closest musical correlate to the intonation phrase level of speech, which is the musical phrase.

Therefore, the nPVI measure was modified to calculate the pnPVI, or the phrase-nPVI, for individual musical phrases. To calculate the overall pnPVI for larger units, such as entire songs, the pnPVI values for each phrase were weighted based on the number of rhythmic events in the phrase and the weighted results were averaged.

RESULTS

Cross-language results

Figure 1 illustrates the overall weighted average pnPVI value for the French and German songs in the study. The marker represents the weighted overall average pnPVI of each language; the bars represent the range of the overall weighted pnPVI values for composers in that language. While the weighted overall average pnPVI is lower for French than for German (47.9 and 48.1, respectively), this is not a significant result when compared to either the average nPVI values calculated by Grabe and Low [START_REF] Grabe | Durational variability in speech and the rhythm class hypothesis[END_REF] of 43.5 and 59.7 or the unexpected nPVI averages found by Huron and Ollen [START_REF] Huron | Agogic contrast in French and English themes: Further support for Patel and Daniele (2003)[END_REF] of 43.7 for French and 42.0 for German. This result indicates that the hypothesis regarding the rhythmic characteristics of stress-timed and syllabletimed languages and their effect on the rhythmic characteristics of vocal music does not hold for the current set of data. What is most significant about this result is that the hypothesis has failed in a sample of a genre of music where the relationship between language and music has traditionally been assumed to be a very strong one.

Cross-composer results

Figure 2 shows the weighted average pnPVI value for songs by individual composers and also illustrates the distribution range of weighted average pnPVIs for songs for each individual composer. 3 For example, the weighted average pnPVI value for Bizet songs ranges from a minimum of 21.6 to a maximum of 76.8, with a weighted average of 49.7. Therefore, the hypothesis that the syllable-timed French language would influence French composers to write musical melodies with a lower amount of durational variability than that exhibited by music influenced by the stress-timed German language has so far not held for a cross-language study, and, with the possible exception of Debussy, has not held robustly for individual composers. There is a slight correlation between the decade of composition and an increase in the average weighted pnPVI value. However, the regression of year of composition against average pnPVI is not significant (r 2 = .0509, df = 1, p < .6).

pnPVI as a function of time

Charting French song pnPVI and German song pnPVI together over time, as in Figure 5, illustrates the trend in each language in relation to the other. While the overall weighted average pnPVI for the data in this study do not support the original hypothesis, for the decade of 1890, the last decade for which there is data for both languages, the pnPVI averages for the two languages (French, 39.4; German 50.0) do support the original hypothesis in a statistically significant way. It is also interesting to note that the trendlines suggest a convergence of French and German nPVI values in the time period from 1860-1870, and the pnPVI averages for both the 1860s and the 1870s roughly indicate this convergence and subsequent divergence. Figure 6 shows the pnPVI trend of individual French composers based on the repertory encoded in the current study. This chart illustrates that the overall decline in the nPVI of French song demonstrated in Figures 3 and5 is not the result of data for one or two composers influencing the results. Only two French composers in the study, Massé and Chausson, had an overall trend of increase in pnPVI; the other ten French composers all exhibit a trend of declination in the pnPVI average of their works as the 19 th century progressed. 4 Some composers, such as Gounod and Saint-Saëns, exhibit a sharp overall decline in nPVI value throughout the 19 th century; others like Fauré and Reyer show a less pronounced trend of declination. Thus the overall decline in nPVI of French songs is not the result of the influence of any one individual composer on the data, but rather seems to be a general trend among French composers.

CONCLUSIONS

The primary hypothesis, demonstrated in previous studies focusing on instrumental music, was that French-influenced vocal music would have a lower nPVI than German-influenced vocal music, reflecting the influence of the rhythmic properties of the spoken language, specifically the greater degree of durational variability present in spoken German than in spoken French. The hypothesis has not held up in a simple comparison between two large groups of songs; the difference between the weighted average pnPVI for all French and German songs was not statistically significant, and with few exceptions there was no clear trend for the weighted overall average pnPVI of individual composers.

However, when pnPVI is plotted as a function of time, there is a clear declination trend for the average pnPVI value of French-influenced music and a slight rising trend for the average pnPVI of Germaninfluenced music throughout the 19 th century. These trends are borne out by both the plot of the overall average pnPVI for each language and by the data for the individual composers. It is unlikely that these trends are the result of changes in the spoken language over that time period; therefore, there must have been stylistic changes in French and German song that caused the nPVI to rise or decline. In combination, the two trends result in the difference between the average nPVI values for each decade approaching and reaching statistical significance by the end of the century. Moreover, these final values match closely the linguistic nPVI results of Grabe and Low [START_REF] Grabe | Durational variability in speech and the rhythm class hypothesis[END_REF].

Figure 1 .

 1 Figure 1. Cross-language average pnPVI .

Figure 2 .

 2 Figure 2. Distribution and weighted average song pnPVI values by composer Worthy of mention from this graph are the low weighted average pnPVI and low distribution range for the Debussy songs, as well as the narrow distribution range (but relatively high weighted average pnPVI) for Chausson and the relatively high weighted average pnPVI and distribution range for Duparc, Schumann and Strauss. However, with the exception of Debussy, there is no clear trend for the individual pnPVI values to be

Figure 3

 3 Figure 3 illustrates the weighted pnPVI of the French songs in the study plotted against the year of their composition. The graph shows the weighted average for the French songs by the decade of composition; the plot for 1840 represents all songs composed between 1840-1849, the plot for 1850 represents all songs composed between 1850-1859, and so on up to 1900, which only represents songs written in the year 1900. The vertical bars represent the range in which the individual songs' weighted pnPVI fell, and the marker and value represent the weighted overall average for songs composed in that decade.

Figure 3 .

 3 Figure 3. Average weighted pnPVI of French songs by decade of composition The dotted trend line illustrates the best-fitting regression line (weighted pnPVI = [-2.4179 x date of composition] + 56.757). The regression of year of composition against average pnPVI is significant (r 2 = .6817, df = 1, p = .02). The chart clearly shows a general trend of declination in average pnPVI value over the time period 1840-1900 for the French songs in this study.

Figure 4

 4 Figure 4 illustrates a similar graph for the German songs in the study. Again, the graph shows the weighted average for the German songs by the decade of composition, the vertical bars represent the range in which the individual songs' weighted pnPVI fell, and the marker and value represent the weighted overall average for songs composed in that decade.

Figure 4 .

 4 Figure 4. Average weighted pnPVI of German songs by decade of composition The dotted trend line illustrates the best-fitting regression line (weighted pnPVI = [0.4929 x date of composition] + 45.107).There is a slight correlation between the decade of composition and an increase in the average weighted pnPVI value. However, the regression of year of composition against average pnPVI is not significant (r 2 = .0509, df = 1, p < .6).Charting French song pnPVI and German song pnPVI together over time, as in Figure5, illustrates the trend in each language in relation to the other. While the overall weighted average pnPVI for the data in this study do not support the original hypothesis, for the decade of 1890, the last decade for which there is data for both languages, the pnPVI averages for the two languages (French, 39.4; German 50.0) do support the original hypothesis in a statistically significant way. It is also interesting to note that the trendlines suggest a convergence of French and German nPVI values in the time period from 1860-1870, and the pnPVI averages for both the 1860s and the 1870s roughly indicate this convergence and subsequent divergence.

Figure 5 .

 5 Figure 5. Cross-language pnPVI plot over time.

Figure 6 .

 6 Figure 6. pnPVI results for individual French composers.

Table 1 .

 1 Mean nPVI results from Huron and Ollen[START_REF] Huron | Agogic contrast in French and English themes: Further support for Patel and Daniele (2003)[END_REF]

				No. of
		(nPVI)	Standard Error	Themes
	American	46.3	1.12	415
	Austrian	42.0	0.65	1194
	Czech	47.1	1.56	232
	English	45.6	0.90	737
	French	43.7	0.73	1188
	German	42.0	0.59	2006
	Hungarian	45.4	1.62	244
	Italian	42.7	1.06	529
	Polish	45.1	1.74	254
	Russian	39.8	0.82	736
	Scandinavian*	45.9	1.79	141
	Spanish	42.5	1.85	108
	* Danish, Swedish, Norwegian (Finnish excluded)

Table 2 .

 2 Composers and number of songs represented in the study.

			German
	Bizet	(24)	Brahms	(52)
	Chausson	(20)	Franz	(61)
	David	(34)	Schubert	(59)
	Debussy	(29)	Schumann	(36)
	Duparc	(14)	Strauss	(33)
	Fauré	(37)	Wolf	(82)
	Gounod	(29)
	Lalo	(15)
	Massé	(20)
	Massenet	(29)
	Reber	(30)
	Reyer	(8)
	Saint-Saëns	(7)
	Total	(296)	Total	(324)

Stylistic pieces such as Chinoise, or any other piece deliberately trying to evoke some "other," were excluded. The cutoff date for inclusion was 1900.

These averages are calculated by weighting the pnPVI of each song, which itself was calculated by weighting the phrases.

Debussy's trendline goes off the scale of the chart for readability purposes; the trendline ends in 1898 with a value of 28.6.


Rui Zhang
email: ruizhang@xmu.edu.cn

Markus G Weinbauer

Peter Peduzzi
email: peter.peduzzi@univie.ac.at

Aquatic Viruses and Climate Change

The viral component in aquatic systems clearly needs to be incorporated into future ocean and inland water climate models. Viruses have the potential to influence carbon and nutrient cycling in aquatic ecosystems significantly. Changing climate likely has both direct and indirect influence on virus-mediated processes, among them an impact on food webs, biogeochemical cycles and on the overall metabolic performance of whole ecosystems. Here we synthesise current knowledge on potential climate-related consequences for viral assemblages, virus-host interactions and virus functions, and in turn, viral processes contributing to climate change. There is a need to increase the accuracy of predictions of climate change impacts on virusdriven processes, particularly of those linked to biological production and biogeochemical cycles. Comprehension of the relationships between microbial/viral processes and global phenomena is essential to predict the influence on as well as the response of the biosphere to global change.

Introduction

Whereas most human interventions on ecosystems are immediate, the impact on climate change acts over long periods of time, leading to slight but continuous alterations. As an example, the predicted 2.6-4.8°C warming, under the conditions of Representative Concentration Pathways 8.5 (IPCC, 2013), for this century is expected to be responsible for species movements and extinctions, as well as for changes in the composition of communities, thus likely altering ecosystem functioning [START_REF] Mooney | Biodiversity, climate change, and ecosystem services[END_REF]. Since global change will probably impact all ecosystem components, it is expected that even the smallest life-forms such as Bacteria, Archaea, eukaryotic microorganisms and viruses of aquatic systems will play important roles as agents and recipients of global climate change [START_REF] Danovaro | Marine viruses and global climate change[END_REF][START_REF] Hutchins | Microorganisms and ocean global change[END_REF].

Beside direct effects by changes in water temperature, others may occur through altered oceanic circulation along with changing habitats, biogeochemical cycles and food webs. Particularly estuaries and continental shelf regions seem to be affected by changed river runoff due to reduced or enhanced precipitation and flooding. This will result in changes in salinity and nutrients, and in the strength and seasonality of circulation patterns [START_REF] Danovaro | Marine viruses and global climate change[END_REF][START_REF] Cozzi | Recent evolution of river discharge in the Gulf of Trieste and their potential response to climate changes and anthropogenic pressure[END_REF]. Changing ocean currents, fluctuations in the depth of the surface mixed layer and stratification might influence light and nutrient availability and ultimately CO2dynamics and the carbon cycle [START_REF] Bauer | The changing carbon cycle of the coastal ocean[END_REF][START_REF] Finke | Nutrients and other environmental factors influence virus abundances across oxic and hypoxic marine environments[END_REF]. Moreover, warming will increase the extent of the oxygen minimum zones (OMZ), which are a globally important sink for nitrogen and a source of CO2. Another global player is the reduction of seawater pH due to enhanced CO2 levels in the atmosphere (ocean acidification, OA). OMZ changes and OA will also influence virus-host interactions.

For inland waters and freshwater systems a whole array of human-mediated threats makes them the most affected ecosystems. Beside pollution and nutrient loads, overexploitation, flow modification, habitat destruction or degradation, climate change is designated as a significant factor for ongoing alterations of these systems [START_REF] Dudgeon | Freshwater biodiversity: importance, threats, status and conservation challenges[END_REF][START_REF] Zweimüller | Effects of climate change on nitrate loads in a large river: the Austrian Danube as example[END_REF]. There is also evidence that climate warming will affect pelagic carbon metabolism and sediment delivery in lakes and carbon sequestration in streams and rivers [START_REF] Battin | The boundless carbon cycle[END_REF][START_REF] Boyero | A global experiment suggests climate warming will not accelerate litter decomposition in streams but might reduce carbon sequestration[END_REF][START_REF] Kritzberg | Warming and browning of lakes: consequences for pelagic carbon metabolism and sediment delivery[END_REF]. Global climate change-related impacts are most striking in the polar regions, where temperature and other factors are changing at more than twice the global average [START_REF] Hoegh-Guldberg | The impact of climate change on the world's marine ecosystems[END_REF]. Due to the major contribution of microbes to ecosystem processes, much attention has been paid to the impact of rapid climate change in Arctic and Antarctic microbial communities (e.g., the European Project on Ocean Acidification, EPOCA). Declines or shifts in these microbial ecosystems will no doubt have implications for entire food webs and biogeochemical fluxes, and polar microbiota can be viewed both as sentinels and amplifiers of global change [START_REF] Vincent | Microbial ecosystem responses to rapid climate change in the Arctic[END_REF].

The global relevance of aquatic viruses has been evident for many years.

Viruses are the smallest and most numerous biological entities in aquatic ecosystems, the majority being bacteriophages [START_REF] Wommack | Virioplankton: Viruses in aquatic ecosystems[END_REF][START_REF] Weinbauer | Ecology of prokaryotic viruses[END_REF][START_REF] Suttle | Marine viruses-major players in the global ecosystem[END_REF]. They are about 10 to 15-fold more abundant than their microbial hosts, and equivalent to the carbon in ca. 75 million blue whales (ca. 10% of prokaryotic carbon by weight; [START_REF] Suttle | Viruses in the sea[END_REF]. The typically high frequency of virus infection in aquatic ecosystems is known to be a major cause of prokaryotic host mortality. Host cell lysis in the marine environment was calculated to be a source of up to 10 9 tons of carbon each day, released from the biological pool [START_REF] Suttle | Marine viruses-major players in the global ecosystem[END_REF][START_REF] Brussaard | Global-scale processes with a nanoscale drive: the role of marine viruses[END_REF]. If the main control of prokaryotic abundance is via protozoan grazing, most of the carbon will be channelled to higher trophic levels (microbial loop). In contrast, if viral lysis accounts for most prokaryotic losses, then carbon and nutrients are diverted away from larger organisms [START_REF] Proctor | Viral mortality of marine bacteria and cyanobacteria[END_REF][START_REF] Wilhelm | Viruses and nutrient cycles in the sea: Viruses play critical roles in the structure and function of aquatic food webs[END_REF].

The biogeochemical consequence of this "viral shunt" (the process of diverting organic carbon away from the grazing food chain via viral lysis of host cells) are changed rates of carbon accumulation in the photic zone (CO2 release to the atmosphere vs. vertical transport to the meso-/bathypelagic zone). Viruses are also involved in shaping the composition of bacterial communities, either by reducing abundant host taxa or even by introducing new genetic information into their hosts (e.g., [START_REF] Zhang | Viruses and flagellates sustain apparent richness and reduce biomass accumulation of bacterioplankton in coastal marine waters[END_REF]. They are the largest and most diverse genetic reservoir on Earth and may boost the resilience of ecosystems by sustaining multiple species with similar or identical biochemical pathways [START_REF] Thingstad | Elements of a theory for the mechanisms controlling abundance, diversity, and biogeochemical role of lytic bacterial viruses in aquatic systems[END_REF]Brussard et al., 2008;[START_REF] Jacquet | Viruses in aquatic ecosystems: important advancements of the last 20 years and prospects for the future in the field of microbial oceanography and limnology[END_REF][START_REF] Brum | Patterns and ecological drivers of ocean viral communities[END_REF][START_REF] Guidi | Plankton networks driving carbon export in the oligotrophic ocean[END_REF][START_REF] Gregory | Marine DNA viral macro-and microdiversity from pole to pole[END_REF].

Elucidating the microbial mediation of carbon-cycle feedbacks to climate change appears to be fundamental for understanding ecosystem responses. This approach would provide a mechanistic basis for carbon-climate modelling [START_REF] Zhou | Microbial mediation of carbon-cycle feedbacks to climate warming[END_REF]. Our substantial lack of knowledge explains why the viral compartment is missing from most climate change models. This review tackles the growing evidence that aquatic viruses interact actively with climate alterations and are key biotic components that can influence the microbial feedback on climate change (compare also [START_REF] Danovaro | Marine viruses and global climate change[END_REF][START_REF] Mojica | Factors affecting virus dynamics and microbial host-virus interactions in marine environments[END_REF].

Impact on viral abundance, distribution and dynamics

In most natural aquatic environments virus communities were found to be highly dynamic, with often pronounced changes in abundance and diversity over broad ranges of space and time. Viral abundance is largely linked to host availability. The numbers of planktonic viruses commonly range between 10 4 and 10 8 ml -1 , being generally higher in inland waters than in marine systems; peak values were reported for very productive estuaries and lakes [START_REF] Peduzzi | Viruses[END_REF][START_REF] Parikka | Deciphering the virus-to-prokaryote ratio (VPR): insights into virus-host relationships in a variety of ecosystems[END_REF]. Exceptionally high virioplankton abundance has been documented in the alkalinesaline lake Nakuru in Kenya, East Africa (up to 7 x 10 9 ml -1 ; [START_REF] Peduzzi | The virus's tooth: cyanophages affect an African flamingo population in a bottom-up cascade[END_REF]. Abundance may be up to three orders of magnitude lower in deep oceanic waters (e.g. [START_REF] Parada | Viral burst size of heterotrophic prokaryotes in aquatic systems[END_REF][START_REF] Magagnini | Viral abundance and distribution in mesopelagic and bathypelagic waters of the Mediterranean Sea[END_REF][START_REF] Li | Lytic viral infection of bacterioplankton in deep waters of the western Pacific Ocean[END_REF][START_REF] Liang | Horizontal and vertical distribution of marine virioplankton: a basin scale investigation based on a global cruise[END_REF]Lara et al. 2017;[START_REF] Muck | Fracture zones in the Mid Atlantic Ridge lead to alterations in prokaryotic and viral parameters in deep-water masses[END_REF]), but virus-induced relative prokaryotic mortality increases with water depth: below a depth of 1000 m almost all of the prokaryotic heterotrophic production in surface sediment is transformed into organic detritus and dissolved organic matter (DOM). This "viral shunt" releases on a global scale 0.37-0.63 Gt carbon year -1 , and is an essential source of labile organic matter for the deep-sea ecosystem [START_REF] Danovaro | Major viral impact on the functioning of benthic deep-sea ecosystems[END_REF]. Recently, [START_REF] Lara | Unveiling the role and life strategies of viruses from the surface to the dark ocean[END_REF] estimated that about 145 Gt of C, 27.6 Gt of N, and 4.6 Gt of P are released annually by the viral shunt in global tropical and subtropical oceans. Moreover, on average, 33.6% (equalling 0.605 !Pg!C!year -1 ) of the globally respired carbon from fluvial systems may pass through a viral loop [START_REF] Peduzzi | Virus ecology of fluvial systems: a blank spot on the map?[END_REF].

Factors affecting virus dynamics and microbial host-virus interactions in the marine environment have been summarized [START_REF] Mojica | Factors affecting virus dynamics and microbial host-virus interactions in marine environments[END_REF]. Typically virus numbers are linked to system productivity, as a result of the balance between production and decay. Eutrophic water bodies contain more virus particles than oligotrophic systems [START_REF] Parikka | Deciphering the virus-to-prokaryote ratio (VPR): insights into virus-host relationships in a variety of ecosystems[END_REF]. The trophic situation can also be very variable on seasonal scales, particularly in running waters with pronounced hydrological dynamics [START_REF] Peduzzi | Virus ecology of fluvial systems: a blank spot on the map?[END_REF] pronouncedly on seasonal scales in inland waters than in the marine environment [START_REF] Wilhelm | Freshwater and marine virioplankton: a brief overview of commonalities and differences[END_REF]2008).

Impact of temperature

The typical viral life cycles (lytic and lysogenic) and replication rates are closely linked with host metabolism. As temperature is a major regulatory factor of microbial growth, an increase in temperature will likely affect the interaction between viruses and their hosts [START_REF] Mojica | Factors affecting virus dynamics and microbial host-virus interactions in marine environments[END_REF]. With increasing prokaryote growth rate, burst size can increase while the length of the lytic cycle decreases [START_REF] Proctor | Calibrating estimates of phageinduced mortality in marine bacteria: ultrastructural studies of marine bacteriophage development from one-step growth experiments[END_REF][START_REF] Hadas | Bacteriophage T4 development depends on the physiology of its host Escherichia coli[END_REF], boosting virus production. Higher temperatures should also increase the contact rates between viruses and hosts [START_REF] Murray | Viral dynamics: a model of the effects of size shape, motion and abundance of single-celled planktonic organisms and other particles[END_REF] and hence potentially infection. Although evidence across systems is scarce, increases in burst size together with increases in production have been described for some natural systems (e.g. [START_REF] Parada | Viral burst size of heterotrophic prokaryotes in aquatic systems[END_REF]. [START_REF] Danovaro | Marine viruses and global climate change[END_REF] suggested that the observed relationship between viral abundance and temperature from different oceanic regions could be used to infer evidence for the potential effect of rising seasurface temperatures. With these compiled data, the strongest effect was detected in temperate-open oceans: a temperature increase of only a few degrees was accompanied by a doubling in viral abundance. Nonetheless, factors influencing virioplankton distribution are clearly more complex than predicted by temperature alone. This is underlined by the observation that, when global data were grouped together, an overall decreasing pattern of viral abundance with increasing temperature was identified. This inverse relationship suggests that latitudinal changes, which influence radiation regimes and trophic characteristics, can display cascade effects on growth rates of hosts and viral infectivity [START_REF] Danovaro | Marine viruses and global climate change[END_REF]. A large data set from the Atlantic Ocean revealed that temperature was important in the Sargasso Sea, but not in the northeast Atlantic [START_REF] Rowe | Constraints on viral production in the Sargasso Sea and North Atlantic[END_REF]. In experiments over short time scales, changes in temperature did not directly influence viral abundance [START_REF] Feng | Effects of increased pCO2 and temperature on the North Atlantic spring bloom. I. The phytoplankton community and biogeochemical response[END_REF].

In the same compilation of literature data, [START_REF] Danovaro | Marine viruses and global climate change[END_REF] showed that, in cold water systems, higher viral production rates were associated with warmer temperatures, whereas the relationship for systems at tropical and mid-latitudes was less clear. They concluded that different oceanic regions would respond differently to changes in surface temperatures caused by climate change. These temperatureassociated changes in viral abundance and production are likely secondary effects caister.com/cimb caused by changes in host cell communities and in virus decay rates [START_REF] Nagasaki | Effect of temperature on the algicidal activity and stability of HaV (Heterosigma akashiwo Virus)[END_REF][START_REF] Wells | Effects of temperature, salinity and clay particles on inactivation and decay of cold-active marine Bacteriophage 9A[END_REF]. [START_REF] Demory | Temperature is a key factor in Micromonas-virus interactions[END_REF] demonstrated that at suboptimum temperatures, lytic cycle kinetics of a Micromonas virus were lengthened and viral yield was reduced. Temperature increase shortened the latent periods, increased the burst size, and affected viral infectivity [START_REF] Maat | Characterization and temperature dependence of arctic Micromonas polaris[END_REF]. Higher temperature will increase viral decay by enhanced activity of extracellular proteases and nucleases [START_REF] Suttle | Mechanisms and rates of decay of marine viruses in seawatert[END_REF][START_REF] Noble | Virus decay and its causes in coastal waters[END_REF][START_REF] Corinaldesi | Viral decay and viral production rates in continental-shelf and deep-sea sediments of the Mediterranean Sea[END_REF][START_REF] Wei | Effects of temperature and photosynthetically active radiation on virioplankton decay in the western Pacific Ocean[END_REF]. In addition, alteration of temperature may affect protein stability and biomolecule elasticity of viral capsid proteins or lipid membranes, and influence the folding and binding of proteins and nucleic acids [START_REF] Mojica | Factors affecting virus dynamics and microbial host-virus interactions in marine environments[END_REF]). An experimental study in two contrasting Arctic systems [START_REF] Lara | Experimental evaluation of the warming effect on viral, bacterial and protistan communities in two contrasting Arctic systems[END_REF] revealed that heterotrophic bacterial and viral abundance, bacterial production and grazing by protists increased at higher experimental temperatures. It remains to be elucidated whether predictable seasonal changes in hosts and viruses are applicable for climate-related long-term and large-scale changes [START_REF] Danovaro | Marine viruses and global climate change[END_REF].

The molecular mechanisms and the environmental factors behind the lysogenic decision are still not well understood [START_REF] Long | Comparison of lysogeny (prophage induction) in heterotrophic bacterial and Synechococcus populations in the Gulf of Mexico and Mississippi River plume[END_REF]. The present climate-related changes in environmental conditions (temperature, circulation of water masses, nutrient availability, alterations in system productivity, coastal mixing with freshwater, etc.) may significantly influence viral life strategies. Lysogeny is thought to be favoured under low nutrient concentrations and high virus-to-host cell ratios [START_REF] Wilson | Lysogenic and lytic production in marine microbial communities[END_REF]. Thus, if nutrient availability becomes limited due to increased vertical stratification caused by rising sea surface temperatures [START_REF] Sarmiento | Response of ocean ecosystems to climate warming[END_REF], a substantial shift to the lysogenic life cycle may be the consequence.

Conversely coastal and estuarine environments may shift to increase favouring of the lytic life-style with large-scale implications on heterotrophic and autotrophic organisms [START_REF] Danovaro | Marine viruses and global climate change[END_REF]. However, [START_REF] Vaqué | Warming and CO2 enhance Arctic heterotrophic microbial activity[END_REF] found rather the inverse trend related to temperature. [START_REF] Knowles | Lytic to temperate switching of viral communities[END_REF] suggested that lysogeny is also favoured at high bacterial production rates (Piggyback-the-Winner model). As temperature increases will influence growth, there could be also a change in viral life strategies. The direct and indirect effects of temperature on viruses and their interaction with hosts remain to be investigated in more detail.

caister.com/cimb 362 Curr. Issues Mol. Biol. Vol. 41

Effect of changing salinity

Freshening of the oceanic environments due to climate change has been discussed particularly for poleward regions, and freshwater increases of the Arctic Ocean are suggested as being linked to respective changes of the North Atlantic as well [START_REF] Peterson | Increasing river discharge to the Arctic Ocean[END_REF][START_REF] Peltier | Atlantic meridional overturning and climate response to Arctic Ocean freshening[END_REF]. Changes in salinity can also influence viral lifestyles [START_REF] Williamson | Environmental factors that influence the transition from lysogenic to lytic existence in the phiHSIC/Listonella pelagia marine phage-host system[END_REF], but experimental studies reveal no consistent pattern regarding the lytic-lysogenic-decision [START_REF] Danovaro | Marine viruses and global climate change[END_REF] and references therein), whereas [START_REF] Bettarel | Ecological traits of planktonic viruses and prokaryotes along a full-salinity gradient[END_REF] found a switch from lytic to lysogenic life styles at high salinity. Recently, viral lysogeny and lysis shifts related to spring-neap tidal cycle were observed in a macrotidal subtropical estuary, which may be caused by freshwater-seawater mixing dynamics [START_REF] Chen | Tide driven microbial dynamics through virus-host interactions in the estuarine ecosystem[END_REF]. Either induction or increased phage latent periods have been found under elevated sodium chloride concentrations. There is evidence that salinity can be of importance for the burst size of infected cells. In waters with high salinity, large burst sizes (up to 200) have been described [START_REF] Guixa-Boixareu | Viral lysis and bacterivory as prokaryotic loss factors along a salinity gradient[END_REF]. Furthermore, in freshwater environments burst sizes are typically higher than in marine systems [START_REF] Peduzzi | Viruses[END_REF].

Mixing of these two environments may result in shifts of host growth rates, DOM availability and burst sizes. An interesting experimental study regarding freshwater and seawater mixing (e.g. as in estuaries) demonstrated that production rates of freshwater viruses sharply declined after seawater addition, followed by a rapid (within 48 h) recovery of the viral populations. Conversely, marine viruses were not significantly affected by mixing with freshwater [START_REF] Cissoko | Effects of freshwater and seawater mixing on virio-and bacterioplankton in a tropical estuary[END_REF]. However, [START_REF] Marine | Freshwater prokaryote and virus communities can adapt to a controlled increase in salinity through changes in their structure and interactions[END_REF] showed that freshwater prokaryote and virus communities can adapt to a controlled increase in salinity through changes in their structure and interactions. Another study has shown the possibility for freshwater viruses to cross into the marine environment and replicate normally [START_REF] Sano | Movement of viruses between biomes[END_REF]). These studies and others [START_REF] Bonilla-Findji | Effect of seawater-freshwater cross-transplantations on viral dynamics and bacterial diversity and production[END_REF][START_REF] Wei | Impacts of freshwater and seawater mixing on the production and decay of virioplankton in a subtropical estuary[END_REF] indicate that viruses can rapidly respond to major shifts in the abundance and community composition of bacterial hosts, which suffer from osmotic shock.

In a meta-analysis [START_REF] Danovaro | Marine viruses and global climate change[END_REF] showed that systems with lower salinity display higher viral abundance. However, these results could reflect the more specific situation of the sampled areas rather than a general trend because this data set was largely from few estuarine systems. It may also be linked to the different nutrient availability and trophic state of the estuarine environments rather than to a direct effect of salinity on the viral assemblages. In addition, [START_REF] Parikka | Deciphering the virus-to-prokaryote ratio (VPR): insights into virus-host relationships in a variety of ecosystems[END_REF] showed in an across-systems study that the ratio of viruses to prokaryote abundance was inversely related to salinity.

Changes in salinity and pH can also influence the extent of virus adsorption to particles [START_REF] Harvey | Use of PRD1 bacteriophage in groundwater viral transport, inactivation, and attachment studies[END_REF][START_REF] Mojica | Factors affecting virus dynamics and microbial host-virus interactions in marine environments[END_REF], thus affecting virus distribution and proliferation. Further, enhanced river runoff to the sea will likely increase the particle concentration in coastal regions. In a riverine environment, for example, the quality, size and age of particles and aggregates, and the exposure time of viruses to aggregates, apparently are the key factors regulating viral abundance [START_REF] Kernegger | Effects of suspended matter quality and virus abundance on microbial parameters: experimental evidence from a large European river[END_REF][START_REF] Peduzzi | Virus ecology of fluvial systems: a blank spot on the map?[END_REF]. Importantly, particles (mainly with organic constituents) appear to play a role as viral scavengers or reservoirs rather than viral factories [START_REF] Weinbauer | Viral ecology of organic and inorganic particles in aquatic systems: avenues for further research[END_REF]. Moreover, adsorption of viruses to suspended particles can stimulate growth of the free-living prokaryotic community, e.g. by reducing viral lysis [START_REF] Peduzzi | Viruses, bacteria and suspended particles in a backwater and main channel site of the Danube (Austria)[END_REF][START_REF] Weinbauer | Viral ecology of organic and inorganic particles in aquatic systems: avenues for further research[END_REF]. In case salinity and particle load play a significant role in community composition, then the predicted sea-level rise, saltwater and freshwater mixing and temperature changes associated with the present global climate change could influence the success of the dominant viral and host taxa.

In those locations where climate change will increase freshwater input and nutrient concentrations, lytic life strategies could become more important through higher burst sizes, increasing infection rates due to the addition of freshwater viruses, and increased growth rates of prokaryotes and phytoplankton [START_REF] Danovaro | Marine viruses and global climate change[END_REF]).

An accelerated prokaryote-virus production cycle will on one hand release more components (e.g. enzymes) that are known as highly active for viral decay [START_REF] Wommack | Virioplankton: Viruses in aquatic ecosystems[END_REF]. On the other hand, increasing amounts of substrate for prokaryotes from the 'viral shunt' will result in larger burst sizes and potentially enhanced rates of adaptation and evolution. Important information could be drawn from additional experimental, proteomic and genomic data analyses in systems with gradients of salinity and from studies on the lifestyle of viruses and their host interactions. The speed and mechanisms of change, which are currently poorly understood, will be the main controlling factors in the shifts along the freshwatermarine continuum [START_REF] Danovaro | Marine viruses and global climate change[END_REF]

Ocean acidification

The uptake of anthropogenic CO2 in ocean waters is reported to alter the pH [START_REF] Riebesell | Sensitivities of marine carbon fluxes to ocean change[END_REF]. Nonetheless, predictions of the effect of ocean pH changes on the viral compartment are difficult. While the direct effects on marine viruses remain uncertain, it is likely that the most significant changes will be caused by the impact on their host organisms, for example on calcifying protists [START_REF] Danovaro | Marine viruses and global climate change[END_REF]. Another example is the observed sharp drop in nitrification under increased CO2 concentrations [START_REF] Hutchins | Nutrient cycles and marine microbes in a CO2-enriched ocean[END_REF], suggesting that viruses from ammoniaoxidising bacteria and archaea might be affected. Furthermore, decreased pH can affect a broad range of physiological processes in microorganisms, e.g. those based on a proton gradient across membranes. Moreover, a significant fraction of nearsurface prokaryotes was found to carry the pigment proteorhodopsin (which can act as a light-driven proton pump), being quite sensitive to even small decreases in pH [START_REF] Fuhrman | Proteorhodopsins: an array of physiological roles?[END_REF]. In the so far largest CO2 manipulation experiment (European Project on Ocean Acidification, EPOCA), complex impacts on different groups of plankton and on biogeochemical cycles were found [START_REF] Riebesell | Arctic ocean acidification pelagic ecosystem and biogeochemical responses during a mesocosm study[END_REF], and special volume of Biogeosciences).

The survival, infectivity and adsorption of some bacteriophages were reported to be sensitive to pH (Harvey et al., 2014) and several studies have demonstrated an influence on the proliferation dynamics of phage-host systems (e.g., [START_REF] Larsen | Phylogenetic analysis of members of the Phycodnaviridae virus family, using amplified fragments of the major capsid protein gene[END_REF]Carreira et al., 2012;[START_REF] Traving | Increased acidification has a profound effect on the interactions between the cyanobacterium Synechococcus sp. WH7803 and its viruses[END_REF][START_REF] Chen | Viral attack exacerbates the susceptibility of a bloom-forming alga to ocean acidification[END_REF]. [START_REF] Highfield | Change in Emiliania huxleyi virus assemblage diversity but not in host genetic composition during an ocean acidification mesocosm experiment[END_REF] showed that the diversity of EhV was much lower in the high-pCO2 treatment enclosure that did not show inhibition of E. huxleyi growth. In the EPOCA experiment, a significant influence of ocean acidification on the relationship between viral and bacterial abundance was found [START_REF] Brussaard | Arctic microbial community dynamics influenced by elevated CO2 levels[END_REF]. Ocean acidification did not affect lytic viral production in mesocosms experiments from the Mediterranean Sea and a Norwegian fjord, but lysogeny was stimulated and either linked to phytoplankton production [START_REF] Tsiola | Bacterial growth and mortality after deposition of Saharan dust and mixed aerosols in the Eastern Mediterranean Sea: a mesocosm experiment[END_REF] or bacterial production [START_REF] Vaqué | Viruses and protists induced-mortality of prokaryotes around the Antarctic Peninsula during the austral summer[END_REF]. In summary, profound effects related to pH-changes on microbial communities and their viruses have been detected, but the topic remains largely unexplored. or solubility pump, the carbonate, the biological pump and the microbial carbon pump [START_REF] Legendre | The microbial carbon pump concept: Potential biogeochemical significance in the globally changing ocean[END_REF]. Conversion of CO2 into biomass and the subsequent sinking of organic and inorganic components of the plankton in the ocean interior are known as the biological carbon pump. The microbial carbon pump is the conversion of organic matter into forms with low bioavailability [START_REF] Jiao | Microbial production of recalcitrant dissolved organic matter: long-term carbon storage in the global ocean[END_REF][START_REF] Legendre | The microbial carbon pump concept: Potential biogeochemical significance in the globally changing ocean[END_REF]. The effect of rising atmospheric CO2 on ocean acidification and carbonation is also receiving current attention. Factors affecting these processes are relevant to understand the functioning of the largest ecosystem on Earth, and to better comprehend the global carbon cycle and its implications on climate [START_REF] Riebesell | Sensitivities of marine carbon fluxes to ocean change[END_REF]. It is still a largely open question how and to what extent the 'viral shunt' influences the efficiency of the biological pump, the microbial carbon pump and the sequestration of carbon in the ocean interior. After viral infection, a varying but substantial fraction of the released organic material can be more or less efficiently utilized by uninfected heterotrophic prokaryotes, thus entering again the food web.

Potential impact of climate change on viruses and carbon cycling

The net effect of the viral shunt is that it detours bacterial production away from being consumed by protists and ultimately converts organic matter into dissolved inorganic nutrients, including respired CO2 [START_REF] Wilhelm | Viruses and nutrient cycles in the sea: Viruses play critical roles in the structure and function of aquatic food webs[END_REF][START_REF] Suttle | Marine viruses-major players in the global ecosystem[END_REF].

Viral particles also make a contribution to the pools and fluxes of DOC, DON and DOP in the global oceans [START_REF] Suttle | Viruses in the sea[END_REF][START_REF] Jover | The elemental composition of virus particles: implications for marine biogeochemical cycles[END_REF][START_REF] Zhang | The fate and biogeochemical cycling of viral elements[END_REF].

In global carbon cycling models viruses are still practically ignored, making it difficult to come up with comprehensive conclusions. One scenario is that viral lysis increases the efficiency of the biological pump by enriching the proportion of carbon in the sinking particulate material [START_REF] Suttle | Marine viruses-major players in the global ecosystem[END_REF]. At the same time, a viral-mediated control on the biological pump will potentially be impacted by climate change in that climate-induced warming of surface oceans could increase the mortality of the pelagic prokaryotes; this would cause an increased release of labile dissolved organic matter (DOM) that can enhance the metabolism and respiration of uninfected cells. Furthermore, a meta-analysis of data from the literature suggested that higher temperatures are associated with exponentially higher decay rates of virioplankton, based on higher levels of exoenzymatic activities [START_REF] Danovaro | Marine viruses and global climate change[END_REF]. [START_REF] Danovaro | Marine viruses and global climate change[END_REF] present a conceptual scheme of the impact on the biological carbon pump and of potential feedback mechanisms. In that concept, viral lysis, together with rising CO2 concentration, cause changes in phytoplankton composition and production. The result would be a modification of both the photosynthetically produced particulate organic (POC) and inorganic (PIC, by calcifying photoautotrophs) carbon. It would also alter the particle export, in particular the relative ratio of PIC to POC in this material. Thus, the flux of CO2 between the ocean surface and the atmosphere would be affected as a possible feedback effect on atmospheric CO2 concentrations. The metabolism of heterotrophic prokaryotic cells could also be enhanced by rising sea-surface temperatures, thus increasing carbon consumption and respiration rates. Two potential scenarios regarding the viralmediated control on the biological pump were suggested [START_REF] Danovaro | Marine viruses and global climate change[END_REF]). On one hand, by altering the pathways of carbon fluxes in the sea -when converting living organic matter into dead particulate organic matter and DOM via cell lysis -the viral shunt could have a negative effect on the biological pump. DOM from cell lysis will be retained to a greater extent in surface waters, much of it converted to DIC through respiration and photodegradation. On the other hand, the viral shunt could favour carbon sequestration by increasing the nutrient availability for primary producers. This could increase the amount of living POC in surface waters, thus enhancing carbon export. In addition, other studies highlighted the role of viral lysis for the release of dense and refractory colloidal aggregates [START_REF] Mari | Dynamics of transparent exopolymeric particles (TEP) production by Phaeocystis globosa caister.com/cimb under N-or P-limitation: a controlling factor of the retention/export balance[END_REF], or for the formation and size increase of organic aggregates [START_REF] Peduzzi | Effect of concentrating the virus-rich 2-200 nm size fraction of seawater on the formation of algal flocs (marine snow)[END_REF], suggesting that viral mortality of host cells can favour carbon transport to the deep sea (viral shuttle; [START_REF] Sullivan | Viral ecology comes of age[END_REF][START_REF] Yamada | Aggregate formation during the viral lysis of a marine diatom[END_REF]. As viruses could also produce positively buoyant aggregates [START_REF] Weinbauer | Ecology of prokaryotic viruses[END_REF], the role of aggregates produced by viruses can be described as viral elevator [START_REF] Weinbauer | Viral ecology of organic and inorganic particles in aquatic systems: avenues for further research[END_REF]. The influence of viral lysis on the stability and formation of aggregates may either increase the retention time of particles in the euphotic zone or increase carbon export to the ocean interior [START_REF] Weinbauer | Viral ecology of organic and inorganic particles in aquatic systems: avenues for further research[END_REF]. However, it is still unclear, whether viruses short-circuit or prime the biological pump [START_REF] Brussaard | Global-scale processes with a nanoscale drive: the role of marine viruses[END_REF]. Changes in the amount of carbon release into the deep will no doubt influence also the functioning of deep-sea ecosystems [START_REF] Smith | Abyssal food limitation, ecosystem structure and climate change[END_REF]. Recently, it has been shown that viruses play a more significant role for carbon fixation than previously thought; this influence is mediated by auxiliary metabolic genes (AMGs) [START_REF] Puxty | Viruses inhibit CO2 fixation in the most abundant phototrophs on earth[END_REF][START_REF] Puxty | Energy limitation of cyanophage development: implications for marine carbon cycling[END_REF]. This suggests a closer link of viral infection to the carbon cycle. In a recent review, it has been argued that metabolic reprogramming of infected cells and viral lysis alter nutrient cycling and carbon export in the ocean; however, the net impacts remain uncertain [START_REF] Zimmerman | Metabolic and biogeochemical consequences of viral infection in aquatic ecosystems[END_REF].

Regarding inland waters the current perception is that the contribution of river networks to fluvial net heterotrophy and CO2 outgassing has been underestimated in the past [START_REF] Battin | Biophysical controls on organic carbon fluxes in fluvial networks[END_REF][START_REF] Raymond | Global carbon dioxide emission from inland waters[END_REF][START_REF] Acuña | Ecosystem Metabolism in River Networks and Climate Change[END_REF]. Almost nothing, however, is known about the significance of the viral shunt in flowing inland waters [START_REF] Peduzzi | Viruses, bacteria and suspended particles in a backwater and main channel site of the Danube (Austria)[END_REF][START_REF] Peduzzi | Virus ecology of fluvial systems: a blank spot on the map?[END_REF]. Most fluvial systems harbour and transport high amounts of organic carbon (dissolved and particulate). Although viral lysis may release only a small fraction to this large organic carbon pool, it could still contribute significantly to the readily utilizable carbon (labile and semi-labile fraction) and its remineralisation in fluvial systems. This should be particularly relevant in these systems, which are characterised by a high proportion of allochthonous (terrestrial) aged and recalcitrant carbon [START_REF] Peduzzi | Virus ecology of fluvial systems: a blank spot on the map?[END_REF]. [START_REF] Pollard | Ultrahigh bacterial production in a eutrophic subtropical Australian river: Does viral lysis short-circuit the microbial loop?[END_REF] reported for the Australian Bremer River that terrestrial DOC was partly returned to the atmosphere as CO2 through bacterial respiration, assisted by bacteriophage lysis of their hosts. This short-circuits the microbial loop. Since streams and rivers are also subjected to climate change-related temperature shifts [START_REF] Zweimüller | Effects of climate change on nitrate loads in a large river: the Austrian Danube as example[END_REF], it is likely that the role of viruses in determining the proportion of organic material in horizontal transport and in processing and remineralisation in fluvial waters will be impacted as well.

Conclusions and outlook

The growing knowledge on virus ecology of marine and inland water environments has increased the incorporation of virus-related processes into aquatic food web models. Nonetheless, in climate change models the role of viruses is difficult to assess due to the rudimentary studies and data. Viruses can be anticipated as the ultimate nanoscale drivers/regulators of life in the effect they can have on organisms. Accordingly, aquatic viral ecology will contribute importantly, as the effects of climate and anthropogenic forcing in aquatic food webs are resolved step by step [START_REF] Brussaard | Global-scale processes with a nanoscale drive: the role of marine viruses[END_REF][START_REF] Zimmerman | Metabolic and biogeochemical consequences of viral infection in aquatic ecosystems[END_REF]. Changes in water temperature no doubt affect microbial growth, respiratory rates and carbon assimilation. This makes it extremely important to understand the effect of global warming on microbial communities and their central role in the carbon cycle. Temperature increases are also likely to impact the interactions between viruses and their host cells. Clearly, an improved understanding of viral responses to present climate change would enhance our chances to predict and adapt to potential consequences of such changes (compare [START_REF] Danovaro | Marine viruses and global climate change[END_REF]. Virus infection of microbial cells has the potential for caister.com/cimb cascading effects in food webs [START_REF] Peduzzi | The virus's tooth: cyanophages affect an African flamingo population in a bottom-up cascade[END_REF]. As ocean temperatures rise, precipitation patterns change and freshening of surface oceans occur, simultaneous and intermingled cascading effects may be the result. Global shifts in viral lifestyles in response to changing climate could have dramatic effects on global biogeochemical cycles via cascading effects.

One substantial drawback is the lack of long-term data sets that could be used to identify the relationships between climatic conditions and microbial processes. In a synthesis of the current knowledge and based on relevant case studies, and on metaanalyses of literature data, [START_REF] Danovaro | Marine viruses and global climate change[END_REF] presented a catalogue of potential consequences and scenarios; some are outlined below together with additional important points: 1.

There is some degree of consensus that the effect of temperature on virus related processes will be significant. Effects might be different at different latitudes and oceanic regions (at high latitudes rising temperatures may promote the viral compartment and depress it at the tropics). Increased vertical stratification due to climate change can lead to large-scale nutrient limitations, altering viral life strategies (lytic vs. lysogenic cycle).

2.

Changes in salinity and the freshwater-marine continuum will probably impact the abundance, proliferation and life strategies of viruses. They may also influence the geographical success of dominant host taxa and subsequently the success of their viral counterparts. Freshening at the poles may increase the input and spread of freshwater groups of hosts and viruses into marine waters, facilitating enhanced crossing over of marine and freshwater taxa. Apparently, climate change-related impacts are particularly severe in polar regions and the microbiota there might be sentinels of global change.

3.

It is currently unclear whether the viral shunt will result in negative or positive effects on the efficiency of the biological pump, and consequently, on the feedback of marine systems on climate. Viruses have the potential to interact with the climate through their contribution to the DOM-pool and to the biogenic particles. 4.

The effect of ocean acidification on marine viruses will be largely via the effects of pH on the host organisms. Since some key metabolic processes of microorganisms are sensitive to changes in pH of the medium, this may profoundly influence the overall functioning of microbial-mediated processes and virus-host interactions. 5.

The role of inland waters, in particular streams and rivers, will be largely reevaluated through the current perception that the contribution of river networks to fluvial net heterotrophy and CO2 outgassing has been underestimated in the past. Increased virus activity will probably contribute significantly to the readily utilizable carbon (labile and semi-labile fraction) and its remineralisation. In fluvial waters, climate change-related temperature shifts will influence the role of viruses in determining the proportion of organic material in horizontal transport and in processing and remineralisation.

6.

Enhanced river runoff to the sea and mixing processes will likely increase the particle concentration at least in coastal regions; such particles are important factors regulating viral abundance. Aquatic aggregates apparently play a role as viral scavengers or reservoirs rather than viral factories, and adsorption of viruses to suspended particles may stimulate growth of the free-living prokaryotic community, e.g. by reducing viral lysis.

From all these considerations it can be concluded that aquatic viruses will be significantly influenced by climate change and that viruses, in turn, can influence processes contributing to climate change. In Fig. 7.1 some potentially important impacts, effects and relations of virus-host systems, facing a global climate change, are outlined. Under the present scenario of climate change, however, it remains unclear whether viruses will ultimately destabilise or even stabilise the dynamics of the living components in ecosystems and the related biogeochemical cycles. Due to the dearth of data it is currently unpredictable whether virus-related processes will amplify or smooth the impact of climate change on aquatic systems [START_REF] Danovaro | Marine viruses and global climate change[END_REF]. These limitations inhibit incorporating virus-related processes into current climate models on the necessary spatial and temporal scales at which climate change scenarios respond and interact with this important compartment of the biosphere. This calls for focused research priorities and long-term data sets to enhance our knowledge about the role of aquatic viruses in the present climate change scenario.

  Knowledge on the interactive role of viruses in global CO2 fluxes is largely in its infancy. Four main CO2 sequestration processes in the ocean are known, the physical caister.com/cimb 365 Curr. Issues Mol. Biol. Vol. 41

Figure 7 . 1

 71 Figure 7.1 Schematic representation of some potentially important impacts of climate change on the virus-host system and potential effects and feedbacks of this biological compartment on some global processes and pools; for details see text.

  . Virus abundance apparently varies more

	caister.com/cimb	360	Curr. Issues Mol. Biol. Vol. 41

Curr. Issues Mol. Biol. Vol. 41

caister.com/cimb