PhD Laura R Bear
email: laura.bear@ihu-liryc.fr

MSc Oumayma Bouhamama

PhD Matthijs Cluitmans

PhD Josselin Duchateau

PhD Richard D Walton

MSc Emma Abell

Msc Charly Belterman

PhD Michel Haissaguerre

PhD Olivier Bernus

PhD Ruben Coronel

PhD Rémi Dubois

"Advantages and pitfalls of noninvasive electrocardiographic imaging"

Keywords: Non-invasive Electrocardiography, Torso Tank, Activation, Repolarization

Background: With increasing clinical use of Electrocardiographic Imaging (ECGI), it is imperative to understand the limits of this technique. The objective of this study is to evaluate a potential-based ECGI approach for activation and repolarization mapping in sinus rhythm.

Method: Langendorff-perfused pig hearts were suspended in a human-shaped torso tank.

Electrograms were recorded with a 108-electrode sock and ECGs with 256 electrodes embedded in the tank surface. Left bundle branch block (LBBB) was developed in 4 hearts through ablation, and repolarization abnormalities in another 4 hearts through regional perfusion of dofetilide and pinacidil. Electrograms were noninvasively reconstructed and reconstructed activation and repolarization features were compared to those recorded.

Results: Visual consistency between ECGI and recorded activation and repolarization maps was high.

While reconstructed repolarization times showed significantly more error than activation times quantitatively, patterns were reconstructed with a similar level of accuracy. The number of epicardial breakthrough sites was underestimated by ECGI and these were misplaced (>20 mm) in location.

Likewise, ECGI reconstructed activation maps demonstrated artificial lines of block resulting from a W-shaped QRS waveform that were not present in recorded maps. Nevertheless, ECGI allowed identification of regions of abnormal repolarization reasonably accurately in terms of size, location and timing.

Conclusions:

This study validates a potential-based ECGI approach to noninvasively image activation and recovery in sinus rhythm. Despite inaccuracies in epicardial breakthroughs and lines of conduction block, other important clinical features such as regions of abnormal repolarization can be accurately derived making ECGI a valuable clinical tool.

Introduction

Electrocardiographic imaging (ECGI) is a non-invasive tool that can be used to panoramically image epicardial cardiac electrical activity using densely sampled body surface potentials and a patient-specific torso model. This technique is being used clinically to reveal electrophysiological substrates in patients with electrical diseases such as abnormally located epicardial breakthroughs, lines of conduction block and regions of delayed depolarization or abnormal repolarization [START_REF] Leong | Repolarization abnormalities unmasked with exercise in sudden cardiac death survivors with structurally normal hearts[END_REF][START_REF] Zhang | Cardiac electrophysiological substrate underlying the ECG phenotype and electrogram abnormalities in brugada syndrome patients[END_REF][START_REF] Andrews | Electrical and Structural Substrate of Arrhythmogenic Right Ventricular Cardiomyopathy Determined Using Noninvasive Electrocardiographic Imaging and Late Gadolinium Magnetic Resonance Imaging[END_REF].

These ECGI reconstructed features could provide the basis for alternative risk-stratification techniques.

In order for this goal to be realized, the reconstructed activation and repolarization maps and the abnormal features identified must be accurate representations of the true electrical abnormalities in these diseased patients. In a recent clinical study the accuracy of an epicardial potential-based ECGI approach has been investigated for the first time during sinus rhythm [START_REF] Duchateau | Performance and limitations of noninvasive cardiac activation mapping[END_REF]. By comparing ECGI reconstructions to epicardial electro-anatomic mapping, several inaccuracies in ECGI maps were highlighted in that study. These included inaccuracies in the position and length of lines of conduction block and the underrepresentation and inaccurate localization of epicardial breakthrough sites (76 ± 37 mm).

These results put into question the accuracy of the electrophysiological substrates that have been previously identified using the same ECGI system in patients, including repolarization abnormalities where validation has not yet been performed. Furthermore the source of these inaccuracies during activation has yet to be determined. The question is whether these are due to 1) the ECGI inverse method itself, 2) the feature extraction methods, or 3) other sources of error (such as respiration movement, torso inhomogeneities, error in sequential activation mapping, or alignment of the ECGI with electro-anatomic geometries).

Many previous validation studies using epicardial potential based ECGI methods have been performed using experimental data from perfused large animal hearts suspended in human shaped torso tanks [START_REF] Oster | Electrocardiographic imaging: Noninvasive characterization of intramural myocardial activation from inverse-reconstructed epicardial potentials and electrograms[END_REF][START_REF] Wang | Application of the method of fundamental solutions to potential-based inverse electrocardiography[END_REF]. These set ups overcome the limitations of clinical validation: being devoid of respiration movement and having the ability to panoramically map the gold-standard epicardial electrical activity mapped to the same geometry. In this manner one can evaluate the efficacy of ECGI inverse and post-processing methods, understand the source of any inaccuracies and develop new methods to overcome them.

In this study, we aim to evaluate the efficacy of an epicardial potential based ECGI approach to reconstruct activation and repolarization maps and their features using a torso tank experimental model.

Materials and Methods

A subset of the experimental data will be made available for the electrocardiographic imaging community, through the EDGAR project (http://www.ecg-imaging.org/), a collaborative effort by the Consortium for ECG Imaging. The analytic methods used are not included as there are open-source applications that are already widely available.

Torso Tank Experimental Setup

The experimental protocol was approved by Directive 2010/63/EU of the European Parliament on the protection of animals used for scientific purposes and the local ethical committee and has previously been described in [START_REF] Bear | Cardiac Electrical Dyssynchrony is Accurately Detected by Noninvasive Electrocardiographic Imaging[END_REF]. Briefly, hearts were excised from pigs (n = 8; 30-40 kg) and perfused in Langendorff mode with a Tyrode's solution, oxygenated with 95%/5% O2/CO2 (pH 7.4, 37°C). An electrode sock (108 electrodes) covering the epicardial surface of the heart was attached to the ventricles. After instrumentation, the heart was transferred to a human-shaped torso tank with 256 electrodes embedded in the surface. In 4 hearts (Group 1), left bundle branch block (LBBB) was induced by radiofrequency ablation. In another 4 hearts (Group 2), regional repolarization heterogeneities were introduced through perfusion of Dofetilide (250 nM) into the non-LAD coronaries and subsequently Pinacidil (30 uM) into the left anterior descending (LAD) artery. For both groups, tank and sock potentials were recorded simultaneously (BioSemi, the Netherlands) during sinus rhythm. These recordings were taken after ablation for Group 1, and before and after the two drug interventions for Group 2. After each experiment, a 3D fluoroscopic scan (Artis, Siemens) was used to obtain the position of the epicardium, coronaries and electrodes with respect to the tank.

Signal Processing and Inverse Reconstruction

Tank and sock channels in which signals were absent or of poor quality on visual inspection were discarded. A multi-lead signal averaging algorithm was used to remove high-frequency noise in the recordings to produce one beat for each activation sequence in each heart [START_REF] Dallet | Combined signal averaging and electrocardiographic imaging method to non-invasively identify atrial and ventricular tachycardia mechanisms[END_REF]. In total, 8 activation sequences (4 from group 1 hearts and 4 from group 2 hearts in control), and 12 recovery sequences (from group 2 hearts in control and the 2 drug interventions). ECGI electrograms were reconstructed from the torso tank potentials to experiment-specific epicardial surfaces using the Method of Fundamental Solutions [START_REF] Wang | Application of the method of fundamental solutions to potential-based inverse electrocardiography[END_REF] with Tikhonov zero-order regularization [START_REF] Tikhonov | Solution of ill-posed problems[END_REF] and the CRESO method [START_REF] Colli-Franzone | A mathematical procedure for solving the inverse potential problem of electrocardiography. analysis of the timespace accuracy from in vitro experimental data☆[END_REF] to define the regularization parameter. For each experiment, the sock electrode positions and the epicardial surfaces were constructed from the 3D fluoroscopic scans using Seg3D [START_REF] Cibc | Seg3D: Volumetric Image Segmentation and Visualization[END_REF].

Activation times were defined from recorded sock and ECGI electrograms as the time of minimum derivative (dV/dt) over the QRS. Recovery times were defined from recorded sock and ECGI-derived electrograms as the time of maximum dV/dt of the T-wave [START_REF] Lux | Repolarization heterogeneity and rate dependency in a canine rapid pacing model of heart failure[END_REF]. A spatio-temporal algorithm developed to define activation times from ECGI electrograms [START_REF] Duchateau | Spatially Coherent Activation Maps for Electrocardiographic Imaging[END_REF] was also investigated for both activation and repolarization. A spatial median filter with 15 mm radius was performed on both recorded and ECGI repolarization times. The 15 mm radius was used as this was found to be the optimal distance to preserve the regions of abnormality in recorded maps, while removing obvious outliers in an automated fashion.

Comparisons and Statistical Analysis

ECGI and sock derived activation and recovery maps were directly compared using the mean absolute error (MAE) and Pearson's correlation coefficient (CC).

The following features of the activation and recovery maps were also quantified and compared. Epicardial breakthrough sites were defined manually from activation maps in hearts in group 2, using the criteria of being a site with an activation time earlier than all surrounding electrodes. When activation was near simultaneous at neighboring electrodes or nodes , the center of the area with <10 ms difference in AT was taken as the breakthrough site. For each activation map, we compared the number of breakthroughs identified using each modality. We also calculate the Euclidean distance and difference in timing between the ECGI-detected and the nearest recorded breakthroughs.

Lines of conduction block were automatically computed from activation maps from hearts in groups 1 and 2 as a jump in the local activation time of 50 ms or more between adjacent electrodes as previously described [START_REF] Rudy | Noninvasive imaging of cardiac electrophysiology and arrhythmia[END_REF] Regions of abnormal recovery from hearts in group 2 were defined as repolarization times outside the normal range of repolarization as defined from sock recordings in control state (no drugs) over all hearts at a cycle length of 600 ms (earlier than 180 ms or later than 310 ms). ECGI and recorded abnormally early and late regions were compared in terms of the mean time in the region, the size of the abnormal region, and the localization error of the center of these regions (defined by the Euclidean offset).

Statistical analysis was conducted using GraphPad Prism 7.04. For each metric, the significance of differences was tested using paired t-tests with p < 0.05 defined as significant. Relationship between variables was evaluated using a Pearson's Correlation. Data are expressed as mean ± SD unless otherwise stated.

Results

Activation and Recovery Mapping

Figures 1 and3 show examples of recorded and ECGI reconstructed activation and repolarization maps, with numerical comparison in Table 1. Qualitative consistency between ECGI and recorded maps was high. The MAE for activations maps was moderately correlated to the QRS duration (R 2 = 0.54; p = 0.01), but there was no correspondence between CC and QRS duration (R 2 = 0.09; p = 0.69). This suggests that the slower activation sequences will demonstrate bigger errors in timing, but that the activation pathway itself is as accurate as with fast activation sequences.

The CC for repolarization maps were not significantly different from those for activation maps using the dV/dT, although the MAE of activation was significantly smaller than that of repolarization (p<0.05). As with activation, the MAE of repolarization was moderately correlated to the T-wave interval (R 2 = 0.43; p=0.02) but not the CC (R 2 = 0.19; p = 0.31).

Using a spatio-temporal approach to compute the activation marker placement significantly improved CC and MAE (p<0.001), but produced less accurate results for repolarization marker placement.

Epicardial Breakthroughs

Figure 1A and B present two examples of recorded (left) and ECGI (right) reconstructed activation maps in normal sinus rhythm with epicardial breakthrough sites marked in yellow (recorded) and grey (ECGI). Table 2 summarizes the numerical comparisons of epicardial breakthrough sites. ECGI tends to smooth over the early activation regions, blending neighboring individual breakthroughs into a large region with very similar activation times. ECGI underestimated the number of epicardial breakthrough sites compared to recorded maps (2.6 ± 0.9 v 1.1 ± 0.3). The breakthrough sites that were captured were substantially shifted in location relative to the nearest recorded breakthrough site. The timing of the ECGI breakthrough sites were similar to the true breakthrough sites (Table 2).

Line of Block

Figure 2A presents example activation maps in hearts with LBBB showing (left) smooth propagation of recorded activation (left). The reconstructed activation map using the min dVdT method (middle) demonstrates a long line of block across the septum between the ventricles. Across all recorded activation maps, lines of block were not present in either normal sinus rhythm nor in the presence of LBBB. However, lines of block were present in 4 of the 8 ECGI reconstructed activation maps using the min dVdT as the activation time marker. This only occurred in hearts with LBBB when QRS duration was longer (Figure 2D). Using a spatio-temporal approach (right) helped to smooth the activation maps (right) but did not completely remove the region of slowed conduction. This method removed 3 of the 4 artificial lines of blocks across the 8 maps.

Recorded electrograms over the septum (Figure 2B) demonstrate a smooth transition of the intrinsic deflection from early to late activation (initially negative to initially positive QRS). For ECGI electrograms (Figure 2C), the intrinsic deflection also shows this transition, but the electrogram is not accurately reconstructed at the artificial line of block with an initial down-stroke before the R-wave.

On the right ventricle, activation is detected on the first downstroke (green electrogram) and shows a sudden transition to the second down-stroke on the left ventricle (cyan electrogram), resulting in the artificial line of block. The spatiotemporal approach considers the delays between electrograms as well as the minimum derivative which helps reduce these artificial jumps in activation time.

Regions of Recovery Abnormality

Figure 3a and 3b present examples of repolarization maps during normal sinus rhythm (3a) in control and (3b) in the presence of regional Pinacidil and Doftelide perfusion through the LAD (black) and non-LAD coronaries, respectively. Qualitative consistency between the early and late repolarization regions of the heart was high. To quantify this, regions of late and early recovery were marked as repolarization times >310 ms and <180 ms. Numerical comparison of early and late recovery areas is presented in Table 2 ECGI correctly identified the presence or absence of early and late recovery regions in all cases. The timing of these regions and the location of the center of these regions were accurately captured with no difference between early or late regions (p = 0.73). ECGI significantly overestimated the size of the early regions (p = 0.02) and underestimated the size of late regions (p = 0.007) by <1 cm 2 (both early and late).

Discussion

In this study we have demonstrated that an epicardial potential based ECGI can be used to reconstruct the general pattern of activation and repolarizations maps in sinus rhythm (normal, LBBB or with repolarization abnormalities) with reasonable accuracy. While some features are accurately captured, others are inaccurate, missing or artificial.

First, during sinus rhythm several epicardial breakthrough sites were missing from ECGI maps compared to those recorded, although they were correct in timing. ECGI also demonstrated to be substantially less accurate at localizing epicardial breakthroughs than at localizing PVC or pacing locations at <5 mm in a torso tank [START_REF] Oster | Electrocardiographic imaging: Noninvasive characterization of intramural myocardial activation from inverse-reconstructed epicardial potentials and electrograms[END_REF][START_REF] Wang | Application of the method of fundamental solutions to potential-based inverse electrocardiography[END_REF]. Results are mostly consistent with clinical validation [START_REF] Duchateau | Performance and limitations of noninvasive cardiac activation mapping[END_REF], except in terms of localization error which was substantially lower in the tank than that seen in patients. This is likely due to respiratory movement of the hearts with the torso compounding localization error clinically (>2 cm in some cases), or the size of the human compared to the pig hearts making it possible for much larger shifts in epicardial breakthroughs. Given that abnormal breakthrough sites have been previously pointed to as potential causal mechanisms of arrhythmia or as markers of disease progression with ECGI [START_REF] Andrews | Electrical and Structural Substrate of Arrhythmogenic Right Ventricular Cardiomyopathy Determined Using Noninvasive Electrocardiographic Imaging and Late Gadolinium Magnetic Resonance Imaging[END_REF], it is important to take these results into account for diagnostic purposes. Other methods to define epicardial breakthrough sites, such as through potential maps or by the shape of the RS portion of the electrograms, may prove more accurate with ECGI reconstructions.

In this study, lines of conduction block were present in some (but not all) ECGI derived activation maps and was absent from all recorded maps. These lines of block were identified only in the presence of LBBB when the QRS duration was long, consistent with validation in a clinical setting [START_REF] Duchateau | Performance and limitations of noninvasive cardiac activation mapping[END_REF].

From analysis of ECGI reconstructed electrograms, it can be seen that this phenomenon arises due to an inaccuracy in the reconstruction electrograms demonstrating a W-shape during the mid-activation phase. Using the min dV/dt method, activation marker placement jumps from the first down-stroke to the second over a small area creating an artificial line of block. We suspect the W-shaped electrograms arise as the reconstructed potentials do not truly represent local epicardial activation but rather a far-field representation of both the epicardial and endocardial electrical activity. This can be seen by the lack of a sharp intrinsic deflection in the ECGI reconstructed electrograms, and the more smooth appearance. This probably has the largest effect on the epicardial regions over the septal region, where indeed the lines of conduction block were usually localized. With further analysis, it may be possible to develop new activation marker placement methods to overcome this limitation and more accurately define epicardial activation times. Indeed, other spatio-temporal activation mapping methods for ECGI do exist that may improve results [START_REF] Erem | Spatiotemporal estimation of activation times of fractionated ECGs on complex heart surfaces[END_REF][START_REF] Cluitmans | In-Vivo Validation of Electrocardiographic Imaging[END_REF]. Furthermore, if the artificial lines of block cannot be eliminated, there are likely other features that can be extracted to differentiate slowed from normal activation such as regions of abnormally late activation or interventricular dyssynchrony (a feature that we have previously demonstrated is accurately reconstructed with the same ECGI approach [START_REF] Bear | Cardiac Electrical Dyssynchrony is Accurately Detected by Noninvasive Electrocardiographic Imaging[END_REF]).

Overall, ECGI reconstructs repolarization as accurately as activation in sinus rhythm when using the dV/dt method to compute markers. While MAE was larger with repolarization, this reflects the larger dispersion of repolarization rather than better accuracy of activation patterns, with both activation and repolarization MAE being correlated to QRS and T-wave intervals, respectively. Unlike with activation, the spatio-temporal approach produced substantially less accurate results with repolarization times. This is unsurprising as the method is based on measuring the delay between neighboring electrograms reflecting activation wave-front propagation, a spatial-connection that does not necessarily exist in repolarization. However, there are many alternative methods available, or that could be developed to define repolarization times that could improve the accuracy of ECGI for mapping recovery. Nevertheless, the derivative approach does allow accurate reconstruction of the location and timing of abnormal recovery regions, and therefore presents a potentially important feature to stratify patients at risk of arrhythmia [START_REF] Zhang | Cardiac electrophysiological substrate underlying the ECG phenotype and electrogram abnormalities in brugada syndrome patients[END_REF]. This work should be considered in light of the limitations inherent in the study. Namely, this study considers only one implementation for solving the inverse problem of electrocardiography.

While this particular epicardial potential based approach is one of the more common methods, there exist a multitude of other methods to not only to describe the cardiac source [START_REF] He | Noninvasive imaging of cardiac transmembrane potentials within threedimensional myocardium by means of a realistic geometry anisotropic heart model[END_REF][START_REF] Simms | Computation of heart surface potentials using the surface source model[END_REF][START_REF] Van Oosterom | A Parameterized Description of Transmembrane Potentials Used in Forward and Inverse Procedures[END_REF], but also to define the forward model [START_REF] Barr | Relating epicardial to body surface potential distributions by means of transfer coefficients based on geometry measurements[END_REF][START_REF] Bradley | The computational performance of a high-order coupled FEM/BEM procedure in electropotential problems[END_REF], solve for the regularization parameter [START_REF] Karoui | Evaluation of fifteen algorithms for the resolution of the electrocardiography imaging inverse problem using ex-vivo and in-silico data[END_REF][START_REF] Barnes | Application of robust Generalised Cross-Validation to the inverse problem of electrocardiology[END_REF], perform ECG signal processing [START_REF] Bear | Effects of ECG Signal Processing on the Inverse Problem of Electrocardiography[END_REF], compute activation and repolarization times [START_REF] Duchateau | Spatially Coherent Activation Maps for Electrocardiographic Imaging[END_REF][START_REF] Erem | Spatiotemporal estimation of activation times of fractionated ECGs on complex heart surfaces[END_REF][START_REF] Cluitmans | In-Vivo Validation of Electrocardiographic Imaging[END_REF] etc. A recent review in the field summarizes these methods and puts them into perspective in terms of clinical applications [START_REF] Cluitmans | Consensus on validation and opportunities of electrocardiographic imaging: From technical achievements to clinical applications[END_REF].

Although our results may be generalizable to those methods, we did not investgate them in this study.

Conclusions

While there is qualitatively high visual consistency between the ECGI derived and recorded activation and repolarization maps, certain important features can be inaccurate, missing or artificial. These limitations arise due to a mismatch in reconstructed electrograms with a W-shaped QRS waveform, resulting in misplacement of activation markers in certain regions. By understanding these limitations, and extracting the features that are accurate, epicardial potential based ECGI can be effectively used in its current form as a useful clinical tool.

Table 1: The mean absolute error (MAE) and the correlation coefficient (CC) between recorded and ECGI

reconstructed activation and repolarizations maps. Activation and repolarization times were computed from ECGI reconstructed signals using either the min/max mdV/dt method or a spatio-temporal approach. Difference between spatio-temporal and dV/dt results (*p<0.01; **p<0.001); Difference between recovery and activation results using the same marker method ( Ϯ p<0.01; ϮϮ p<0.001).

MAE (MS

Table 2 :

 2 Comparison of specific features in activation and repolarization maps. Activation times were computed from ECGI reconstructed signals using a spatio-temporal approach, and repolarization times using max mdV/dt.

	)	CC

Acknowledgements

This work was supported by the French National Research Agency (ANR-10-IAHU04-LIRYC), the Leducq foundation transatlantic network of excellence RHYTHM transatlantic network (16CVD02) and the National Institute of General Medical Sciences of the National Institutes of Health (P41 GM103545-18).

Conflict of interest: MC is part-time employed by Philips Research.


Elena Kazakou
email: elena.kazakou@cefe.cnrs.fr

Guillaume Fried

Olivier Gimenez

Aurélie Metay

A plant trait-based response-and-effect framework to assess vineyard inter-row soil management

Keywords: cover crop, functional traits, tillage, vineyard, weed communities

Biodiversity impacts ecosystem properties and ecosystem services provided by those ecosystems. In this respect, weeds have an important role in maintaining field biodiversity, when balanced with their potential negative impact on crop yield and quality. Trait-based approaches, originally developed in the field of comparative ecology, allow describing weed species responses to management practices in annual crop systems. Here, we aimed at extending the trait-based approach to the spontaneous vegetation of perennial cropping systems, such as vineyards. We adapted the response-effect framework for perennial cultures and especially the vegetation for different soil management practices (tillage, cover crops, spontaneous vegetation) considered as alternatives to the use of herbicides. Soil management practices act as environmental filters that determine the composition and structure of vegetation, which, in turn, modify grapevine growth conditions in the vineyard. We tested this approach in a Mediterranean vineyard where we characterized during 2 years the responses of different components of weed communities (specific and functional composition and dynamics) in three inter-row management practices (tillage, cover crops and mowing spontaneous vegetation) and their effects on several grapevine processes (vine yield, vine leaf water potential and assimilable nitrogen in must).

Introduction

Biodiversity impacts ecosystem properties and ecosystem services provided by those ecosystems [START_REF] Cardinale | Biodiversity Loss and Its Impact on Humanity[END_REF][START_REF] Diaz | Plant Functional Types and Ecosystem Function in Relation to Global Change[END_REF][START_REF] Chapin | Consequences of Changing Biodiversity[END_REF][START_REF] Tilman | The Influence of Functional Diversity and Composition on Ecosystem Processes[END_REF]. The underlying hypothesis is that species differ in the efficiency of resource use (resource use complementarity) and/or in how they modify the surrounding environment in ways that impact other species [START_REF] Wood | Functional Traits in Agriculture : Agrobiodiversity and Ecosystem Services[END_REF][START_REF] Cardinale | Biodiversity Loss and Its Impact on Humanity[END_REF]). As a result, improving plant diversity (specific or genetic) in agricultural systems has been a key issue in agriculture over recent years [START_REF] Litrico | Diversity in Plant Breeding : A New Conceptual Framework[END_REF][START_REF] Tilman | Productivity and Sustainability Influenced by Biodiversity in Grassland Ecosystems[END_REF][START_REF] Cardinale | Biodiversity Loss and Its Impact on Humanity[END_REF]. In this context, weeds have an important role in maintaining field biodiversity, when it is balanced with their potential negative impact on crop yield and quality [START_REF] Storkey | A Functional Group Approach to the Management of UK Arable Weeds to Support Biological Diversity[END_REF]). More precisely, weeds are a major problem in crop production either through competing for resources or reducing crop quality (Naylor and Lutman 2002). At the same time, weeds can in some cases provide additional services to provisioning service of yield (such as pollination, limitation of soil erosion, "traps" for disease agents etc.). The use of key ecological concepts is an important requirement for quantifying the positive contribution of weeds to maintaining biodiversity and ecosystem services without compromising yield must therefore be set in the context of these dis-services associated with weeds [START_REF] Storkey | A Functional Group Approach to the Management of UK Arable Weeds to Support Biological Diversity[END_REF].

Related to this, to manage co-occurring to cultivated plant diversity (weeds, spontaneous vegetation or cover crops) it seems essential to identify assembly rules of complex weed communities and to recognize groups of species that similarly respond to a set of management practices, interact with biotic and biotic components of the agro-system or affect the ecosystem functioning [START_REF] Navas | Trait-Based Approaches to Unravelling the Assembly of Weed Communities and Their Impacts on Agro-Ecosystem Functionning[END_REF].

Several studies have focused mostly on the taxonomic characterization of the composition and the structure of weed communities occurring in cropping systems to predict their response to agricultural management practices [START_REF] Fried | Environmental and Management Factors Determining Weed Species Composition and Diversity in France[END_REF][START_REF] Storkey | Managing Arable Weeds for Biodiversity[END_REF]. However, functional trait diversity, rather than the diversity of species per se, is a facet of biodiversity most directly related to species responses on different management practices and thus consequences to ecosystem functioning [START_REF] Naeem | Disentangling Biodiversity Effects on Ecosystem Functioning: Deriving Solutions to a Seemingly Insurmountable Problem[END_REF][START_REF] Cadotte | Beyond Species: Functional Diversity and the Maintenance of Ecological Processes and Services[END_REF]. Trait-based approaches, originally developed in the field of comparative ecology, have permitted to describe weed species responses to management practices in annual crop systems [START_REF] Booth | Assembly Theory Applied to Weed Communities[END_REF]Gaba, Fried, Kazakou, Chauvel and Navas 2013;[START_REF] Garnier | A Trait-Based Approach to Comparative Functional Plant Ecology: Concepts, Methods and Applications for Agroecology[END_REF][START_REF] Gunton | Functional Traits Relating Arable Weed Communities to Crop Characteristics[END_REF].

The aim of this paper is to extend the trait-based approach to the spontaneous vegetation of perennial cropping systems, namely vineyards. Only a few studies have dealt with the taxonomic characterization of weed communities in those systems (Gago, Cabaleiro and Garcia 2007;[START_REF] Monteiro | Influence of Cover Crop on Water Use and Performance of Vineyard in Mediterranean Portugal[END_REF][START_REF] Steenwerth | Effects of Various Vineyard Floor Management Techniques on Weed Community Shifts and Grapevine Water Relations[END_REF][START_REF] Tesic | Influence of Vineyard Floor Management Practices on Grapevine Vegetative Growth, Yield, and Fruit Composition[END_REF] and none of them have used the traitbased approach. According to the response-effect framework (Fig. 1a; [START_REF] Lavorel | Predicting Changes in Community Composition and Ecosystem Functioning from Plant Traits[END_REF][START_REF] Lavorel | Plant Functional Effects on Ecosystem Services[END_REF][START_REF] Suding | Scaling Environmental Change through the Community-Level: A Trait-Based Response-Effect-Framework for Plants[END_REF], environmental drivers act as filters sorting species according to the value of traits (response traits), which results in a functional structure of communities impacting ecosystem functioning (effect traits). The ultimate goal of responseeffect analyses should be the formulation of parsimonious quantitative relationships expressing the different components of each ecosystem function in relation to particular traits [START_REF] Lavorel | Predicting Changes in Community Composition and Ecosystem Functioning from Plant Traits[END_REF]. These relationships would make it possible to use traits to scale from individual plants and the communities they form to the ecosystem level [START_REF] Dawson | Grouping plants by their form-function characteristics as an avenue for simplification in scaling between leaves and landscapes[END_REF]. So, to apply this framework, it is important to use arguments about scaling through the community level by integrating two components: (1) how a community responds to changes, and (2) how that modified community affects ecosystem processes [START_REF] Suding | Scaling Environmental Change through the Community-Level: A Trait-Based Response-Effect-Framework for Plants[END_REF]. This response-effect framework has been tested and successfully applied in grasslands to understand how the different levels of land-use impact ecosystem services through the changes in vegetation but not yet tested in cultivated systems [START_REF] Gross | Plant Response Traits Mediate the Effects of Subalpine Grasslands on Soil Moisture[END_REF][START_REF] Minden | Testing the Effect-response Framework: Key Response and Effect Traits Determining above-Ground Biomass of Salt Marshes[END_REF].

Moreover, this approach provides a mechanistic understanding of the linkages between biodiversity and ecosystem functioning [START_REF] Renting | Exploring multifunctional agriculture. A review of conceptual approaches and prospects for an integrative transitional framework[END_REF]. As some trait values vary with environmental conditions and agricultural management practices (response traits) and can affect ecosystem functioning (effect traits), this framework could be used to develop particular trait-based management strategies that can be implemented in farming systems to increase multiple ecosystem services as well as to manage trade-offs among ecosystem services in agriculture [START_REF] Wood | Functional Traits in Agriculture : Agrobiodiversity and Ecosystem Services[END_REF]. However, most research focused on using traits to understand how biodiversity in agricultural systems responds to management practices, rather than on understanding how biodiversity impacts agroecosystem services. In this paper, we adapt the response-effect framework for perennial cultures and more specifically the vegetation under different soil management practices (tillage, cover crops, spontaneous vegetation) considered as alternatives to the use of herbicides between rows. We hypothesized that soil management practices act as environmental filters, which determine the composition and structure of vegetation, which in turn modify grapevine growth conditions in the vineyard (Fig. 1b).

Next, we tested this approach in a Mediterranean vineyard where we characterized during 2 years the responses of different components of weed communities (taxonomic and functional composition and dynamics) in three inter-row management practices (tillage, cover crops and managed spontaneous vegetation) and their effects on several grapevine processes (vine yield, vine leaf water potential and assimilable nitrogen in must).

Insert Figure 1, here

Vineyard management inter-row practices as a gradient of disturbance and competition intensity

Before the 1970s, vegetation between vine rows was traditionally managed by mechanical weeding based on soil tillage. Following the generalized use of chemical weed control and the disappearance of tillage, important shifts in weed community composition were observed between the 1970s and the 1990s [START_REF] Barralis | Evolution de La Flore Adventice Du Vignoble de Côte-d'-Or Sous La Pression Des Techniques D'Entretien Des Cultures[END_REF][START_REF] Maillet | Evolution de La Flore Adventice Des Vignobles Du Montpellierais Sous La Pression Des Herbicides[END_REF].

However, health and environmental concerns about the impact of chemicals and deep tillage have recently caused changes in weed management practices [START_REF] Monteiro | Reduced Rates of Residual and Post-Emergence Herbicides for Weed Control in Vineyards[END_REF][START_REF] Moreira | Entretien Du Sol et Évolution de La Flore[END_REF]. Currently, grape growers can choose between two main weed control methods, alternative to chemical control, used exclusively or in combination: reduced tillage in inter-rows and/or the use of a plant cover (temporary or permanent, spontaneous or sown, in rows or inter-rows) [START_REF] Gago | Preliminary Study of the Effect of Soil Management Systems on the Adventitious Flora of a Vineyard in Northwestern Spain[END_REF]. The practice of cover cropping is currently increasing in vineyards as it provides various ecosystem services in relation to the soil (erosion), the crop (control of vegetative development, and the resulting conditions of yield formation and disease development) and the environment (limited use of pesticides as herbicides, or fungicides) (see [START_REF] Ripoche | Changing the soil surface management in vineyards: Immediate and delayed effects on the growth and yield of grapevine[END_REF] for related references). But introducing a second crop can lead to undesirable competition for soil resources such as water and nitrogen [START_REF] Celette | Spatial and Temporal Changes to the Water Regime of a Mediterranean Vineyard due to the Adoption of Cover Cropping[END_REF] and result in a problem of trade-off between provisioning and regulating ecosystem services. For this reason, vineyards represent a relevant model, in which inter-row soil management ranges from regular soil cultivation (tillage), as in annual crops, to mowing spontaneous vegetation, as in semi-natural permanent grasslands. Gaba et al. (2013) proposed a comparative description of the environmental gradients created mainly by annual cropping system. Here, we represent three inter-row vineyard management practices (tillage, cover crop and spontaneous vegetation) as a double gradient of soil disturbance and competition intensity with tillage being the most disturbed habitat based on Grime's theory [START_REF] Grime | Plant Strategies and Vegetation Processes[END_REF]. Tillage corresponds to high disturbance, defined according to [START_REF] White | Natural Distrubance and Patch Dynamics: An Introduction[END_REF] as "any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability or the physical environment" (Fig. 2a). The outcome of tillage varies with respect to both characteristics of the operation, such as depth, number of passes and the characteristics of the soil that is being tilled (see Gaba et al. 2013 for a detailed description). At low levels of disturbance strong competitors exclude competitively inferior species and communities are dominated by a few species. Intermediate levels of disturbance, however, disrupt competitive hierarchies by increasing levels of mortality and thus making free space available for recruitment of competitively inferior species [START_REF] Connell | Diversity of tropical rainforests and coral reefs[END_REF]. These patterns are also affected by spatio-temporal variability in disturbance: how often a disturbance occurs (i.e. frequency), how large the disturbance is (i.e. area or extent) and time since the last disturbance (i.e. time).

When the extent of disturbance is considered, areas that are too large will eliminate all species, areas that are too small will have little or no impact, whereas intermediate areas may disrupt competitive exclusion and allow establishment of new species in the disturbed patches [START_REF] Wilson | The Intermediate Disturbance Hypothesis of Species Coexistence Is Based on Patch Dynamics[END_REF].

Studies in annual crops systems have described tillage as a filter that influences weed species composition and weed seed distribution in the soil seed bank (for exemple [START_REF] Cardina | Long-Term Tillage Affects on Seed Banks in Three Ohio Soils[END_REF][START_REF] Cousens | A Model of the Effects of Cultivation on the Vertical Distribution of Weed Seeds within the Soil[END_REF]. According to Grime's theory, tillage treatment will result in less diverse communities dominated by a small number of species whereas an intermediate disturbance (corresponding to vegetation cover treatment frequently mowed) will result in more diverse and equitable communities [START_REF] Grime | Trait Convergence and Trait Divergence in Herbaceous Plant Communities: Mechanisms and Consequences[END_REF]. Under low disturbance, corresponding to the spontaneous cover, competitive exclusion by the dominant species is expected to occur [START_REF] Grime | Trait Convergence and Trait Divergence in Herbaceous Plant Communities: Mechanisms and Consequences[END_REF], due to light, nutrient or water competition (Fig. 2a). At low intensities or frequencies of disturbance there is a balance between competitive exclusion and loss of competitive dominant species by disturbance. As indicated in Fig. 2a, we assumed that the intensity of soil tillage (from no tillage treatments to conventional tillage treatments) corresponds to a disturbance gradient, whereas the degree of vegetation cover, from spontaneous vegetation (with varying and irregular cover according to the weed species) to sowed cover crop (with the sowed species being well implanted and thus dominant species) corresponds to a competition intensity gradient (for light, nutrient or soil water content).

Insert Figure 2 here

Effects of different inter-row management practices on communities' composition and structure and ecosystem functioning

The effects of different inter-row soil management practices in vineyards on communities' composition and structure and ecosystem processes have been discussed in the literature (synthesis in Table 1) (we focus on non chemical management methods). Conflicting results were found considering the effects of tillage on plant diversity and composition, possibly as a result of community fluctuations rather than deterministic changes in community composition (for example [START_REF] Derksen | Impact of Agronomic Practices on Weed Communities: Tillage Systems[END_REF][START_REF] Legere | Short Communication: A Corn Test Crop Confirms Beneficial Effects of Crop Rotation in Three Tillage[END_REF][START_REF] Gago | Preliminary Study of the Effect of Soil Management Systems on the Adventitious Flora of a Vineyard in Northwestern Spain[END_REF] found that plant cover crop showed a much lower number of weed species, mostly therophytes [START_REF] Beuret | L'entretien Du Sol En Viticulture[END_REF][START_REF] Maillet | Evolution de La Flore Adventice Des Vignobles Du Montpellierais Sous La Pression Des Herbicides[END_REF] irrespective to soil management technique). A limitation of using plant cover (spontaneous or sown) is the competition for resources including water, soil nutrients and light, which can compromise vineyard vigor. However recent studies on intercropping in vineyards have shown that in some situations, water stress may not be greater than in bare soil vineyards [START_REF] Celette | Spatial and Temporal Changes to the Water Regime of a Mediterranean Vineyard due to the Adoption of Cover Cropping[END_REF]. The advantage of some cover crops is the possibility to use them to manage weeds through several mecanisms. First, competition between weeds and cover crops for light and soil resources will occur to varying degrees based on the vineyard environment and management [START_REF] Fredrikson | Cover Crop and Floor Management Affect Weed Establishing Coverage and Density in an Oregon Vineyard[END_REF]. Second, allelopathic suppression of weeds has been observed upon decomposition of legume residues, such as clovers (Dyck andLiebman 1994, Liebman andDavis 2000) and non leguminous residues, such as cereal rye (Weston 1996).

On the other hand spontaneous cover treatment can be chosen as a costless tradeoff for the winegrowers between improving soil properties, limiting mechanical work and maintaining vine production. According to the objectives of winegrowers (limiting weed competition when resources are limiting or improving soil structure and improving soil bearing capacity), the management of the spontaneous treatment should be adapted each year in agreement with the climatic constraints: for example, the number and dates of mowing could be adapted and the spontaneous treatment may be retained or not.

Insert Table 1 here

Functional structure and species response traits to different management practices and ressources availability

The functional characterization of weed responses to specific components of management has been successfully developed in several recent studies [START_REF] Booth | Assembly Theory Applied to Weed Communities[END_REF][START_REF] Fried | Trajectories of Weed Communities Explained by Traits Associated with Species' Response to Management Practices[END_REF][START_REF] Gunton | Functional Traits Relating Arable Weed Communities to Crop Characteristics[END_REF][START_REF] Navas | Trait-Based Approaches to Unravelling the Assembly of Weed Communities and Their Impacts on Agro-Ecosystem Functionning[END_REF][START_REF] Storkey | Modelling Seedling Growth Rates of 18 Temperate Arable Weed Species as a Function of the Environment and Plant Traits[END_REF]2006) showing that for annual crop species, the phenological traits of weeds (timing of emergence) are one of the key drivers of weed community assembly in responses to crop sowing dates and harvest dates.

However, in the case of perennial cropping systems only taxonomical diversity indices of weed species have been used to compare the effect of different management practices so far (e.g. [START_REF] Barralis | Evolution de La Flore Adventice Du Vignoble de Côte-d'-Or Sous La Pression Des Techniques D'Entretien Des Cultures[END_REF]Dastgheib and Frampton, 2000 for vineyards) while functional traits were only used very recently to assess the services of sown cover crop [START_REF] Gamour | Using Functional Traits to Assess the Services Provided by Cover Plants: A Review of Potentialities in Banana Cropping Systems[END_REF].

According to the response-effect framework, response traits to environmental filters change community's functional structure and diversity and thus impact ecosystem processes via changes in the representation of ecosystem-effect traits [START_REF] Suding | Scaling Environmental Change through the Community-Level: A Trait-Based Response-Effect-Framework for Plants[END_REF]Fig. 1a). It has been assumed that the most abundant species are often more functionally important simply due to greater representation [START_REF] Grime | Benefits of Plant Diversity to Ecosystems: Immediate, Filter and Founder Effects[END_REF][START_REF] Garnier | Plant Functional Markers Capture Ecosystem Properties During Secondary Succession[END_REF][START_REF] Balvanera | Applying Community Structure Analysis to Ecosystem Function: Examples from Pollination and Carbon Storage[END_REF]. This assumption forms the basis of the dominance hypothesis proposed by [START_REF] Grime | Benefits of Plant Diversity to Ecosystems: Immediate, Filter and Founder Effects[END_REF] under the name of the mass-ratio hypothesis, suggesting that community effects on ecosystem functioning are mainly determined by the traits of the dominant species. [START_REF] Garnier | Plant Functional Markers Capture Ecosystem Properties During Secondary Succession[END_REF] described the functional structure of a community through value and range of traits by an estimator known as the Community Weighted Mean (CWM). CWM represents the average trait value for a unit of biomass within a community. In other cases, species functional effects may not scale as directly with abundance due to nonadditive interactions as suggested by the niche complementarity hypothesis [START_REF] Petchey | Functional Diversity: Back to Basics and Looking Forward[END_REF]. According to this hypothesis, environmental filtering may affect functional trait diversity (i.e. trait convergence or divergence) within communities through mechanisms such as complementarity resource use [START_REF] Petchey | Functional Diversity: Back to Basics and Looking Forward[END_REF].

In Table 2 we provide a summary of the response of traits according to different inter-row soil management and the corresponding sources. Based on previous results in other environments (for a review see Garnier, Navas and Grigulis 2016), highly disturbed habitats select species with rapid completion of the life cycle and high fecundity (low seed mass, onset of flowering at the end of favorable season, low reproductive height), corresponding to the ruderal species strategy (R) [START_REF] Grime | Plant Strategies and Vegetation Processes[END_REF]; Table 2). An intermediate disturbance condition favors the coexistence of competitive species and stress-tolerant species (due to the resources limitation) [START_REF] Mackey | The Diversity-Disturbance Relationship: Is It Generally Strong and Peaked?[END_REF]. Unproductive habitats select perennial species with slower plant growth, longer life spans, denser tissues, in which resources are conserved more efficiently (stress-tolerant S). Stress-tolerant species, found in low stress, low disturbance habitats, allocate resources to maintenance and defenses, such as anti-herbivory [START_REF] Grime | Plant strategies, vegetation processes, and ecosystem properties[END_REF]. Finally productive habitats (no disturbed and no stressed habitats) select mostly annual species for the ability to pre-empt resources by foraging (competitors, C) (Table 2).

Competitors are primarily composed of species with high relative growth rate, short leaf-life, relatively low seed production, and high allocation to leaf construction. They persist in high nutrient and low disturbance environments. Thus, in contrast to the denser tissues, low specific leaf area and concomitantly slow growth of stress-tolerators [START_REF] Poorter | A Comparison of Specific Leaf Area, Chemical Composition and Leaf Construction Costs of Field Plants from 15 Habitats Differing in Productivity[END_REF][START_REF] Poorter | Is Inherent Variation in RGR Determined by LAR at Low Light and by NAR at High Light?[END_REF][START_REF] Weiher | Challenging Theophrastus: A Common Core List of Plant Traits for Functional Ecology[END_REF], both competitors and ruderal species are characterized by high specific leaf area and faster relative growth rates (resulting from greater internal conductivity and lesser investment in structural tissues), with ruderal species investing more in the reproductive phase of the life cycle (Table 2).

We assume that in tillage treatments, tolerance and escape are the two types of responses that species will adopt resulting in small size, with high growth rates (as found for example in [START_REF] Storkey | A Functional Group Approach to the Management of UK Arable Weeds to Support Biological Diversity[END_REF][START_REF] Fried | Trajectories of Weed Communities Explained by Traits Associated with Species' Response to Management Practices[END_REF]. Plants growing in nutrient-poor or dry environments will increase their ability to access soil resources (by increasing root biomass or their capacity to fix atmospheric nitrogen). In cover crop treatments, it is expected that the less competitive weed species will be excluded, while only some competitive species that can rapidly reach a high size (relative to the cover crop), high specific root length and depth, and efficient nutrient use strategies would be able to maintain Alternatively, we assume that spontaneous species having different traits and using resources differently than the cover crop could also maintain (e.g. early flowering weed species able to produce seeds before the closure of the canopy of the cover crop).

In addition, we hypothesize that disturbance (represented by tillage treatment) act as a filter resulting in the convergence of traits within communities (i.e. reduction in trait variation with increased disturbance), whereas cover crop and spontaneous vegetation will result to less similar species in the communities according to the limiting similarity hypothesis (Fig. 2b). This means that the functional divergence (i.e. the degree to which the distribution of species abundances in niche space maximizes total community variation in functional characters) of the different weed species is the result of species separate niches and thus complementary in resource use.

Insert Table 2 here

Effect traits of weed communities and services on vineyard ecosystems

Several studies have shown that many ecosystem properties (for example above-ground net primary productivity, litter decomposition, soil nitrogen, soil water content, digestibility…) are controlled by the traits of dominant species or/and functional diversity of communities (see [START_REF] Garnier | Planr Functional Diversity Organism Traits, Community Structure and Ecosystem Properties[END_REF] for a detailed review). These numerous studies were conducted in diverse ecosystems (secondary succession, grasslands, forests or serpentine ecosystems) but none of them considered perennial cropping. Recently, [START_REF] Gamour | Using Functional Traits to Assess the Services Provided by Cover Plants: A Review of Potentialities in Banana Cropping Systems[END_REF] discussed how the trait-based approach could be used to assess the services delivered in cover cropped banana cropping systems and identified which effect traits are related to these services.

Here we adapt the synthesis about traits and ecosystem services proposed by [START_REF] De Bello | Towards an Assessment of Multiple Ecosystem Processes and Services via Functional Traits[END_REF] to assess the contribution of vegetation species traits to different ecosystem services related to vineyards (Table 3). Following de Bello et al. ( 2010), we consider that there is a group of traits such as growth form, canopy density and plant size as well as the root system that are involved in water regulation and soil stability. We assume that leaf and litter traits influence vine growth and soil fertility via an increase in the decomposition and mineralization processes (as shown for tree species by [START_REF] Wardle | Linkages between plant litter decomposition, litter quality, and vegetation responses to herbivores[END_REF]. In order to expand the trait-services approach to services such as pollination (with different trophic groups are involved) we should consider different trophic levels [START_REF] Lavorel | A Novel Framework for Linking Functional Diversity of Plants with Other Trophic Levels for the Quantification of Ecosystem Services[END_REF]. To date, this approach has never been tested in vineyards or any other agricultural system (except in grasslands). The challenge for future works is to establish the linkages between traits and services to provide a basis for practical agroecosystem management and decision-making.

Insert Table 3 here

A case study: Short-term dynamics of weed communities in response to different soil management and effects in a vineyard performance of southern France

In Mediterranean regions, adaptation to climate fluctuations is a recurrent management problem in agricultural production [START_REF] Ripoche | Changing the soil surface management in vineyards: Immediate and delayed effects on the growth and yield of grapevine[END_REF]. In perennial systems, like vineyards, adaptation is possible through canopy management [START_REF] Smart | Canopy management to improve grape yield and wine quality: Principles and practices[END_REF], fertilization, irrigation, or soil surface and intercropping management (Celette and Gary, 2006;[START_REF] Chifflot | Beneficial Effects of Intercropping on the Growth and Nitrogen Status of Young Wild Cherry and Hybrid Walnut Trees[END_REF]. However only 14% of vineyards in the Mediterranean regions are intercropped, (Mezière et al. 2009) as wine growers in those regions fear occasional episodes of strong competition for water between the two crops and are reluctant to introduce cover crops despite the regulating services they would provide [START_REF] Ripoche | Changing the soil surface management in vineyards: Immediate and delayed effects on the growth and yield of grapevine[END_REF]. In this study, we compare response traits of associate plant diversity in three management practices and test their links with agroecosystem properties. This first attempt to adapt the trait-response framework to vineyards may permit to demonstrate how management practices can achieve target traits and those traits will achieve goals for the rates of ecosystem properties and services (as suggested at the theoretical framework of [START_REF] Wood | Functional Traits in Agriculture : Agrobiodiversity and Ecosystem Services[END_REF]. More precisely we tested the effect of three management practices (tillage, managed spontaneous vegetation and cover crop) commonly used in Mediterranean vineyards on different components of taxonomic and functional diversity.

The field experiment is detailed in (Guilpart, Metay, and Gary 2014). Grapevines Depending on the regime of disturbance due to practical operations in the vineyard, weed sampling covers was conducted at several dates during a year, especially before and after treatments and at least two years to record weed communities responses (measured traits are detailed in Figures 3 and4). We also monitored vine yield and growth, and water and nitrogen grapevine status, as previous research has documented significant effects of cover crops on these key parameters [START_REF] Ingels | Effects of Cover Crops on Grapevines, Yield, Juice Composition, Soil Microbial Ecology, and Gopher Activity[END_REF]Tesic, Keller, and Hutton 2007b;[START_REF] King | Vineyard 15N, Nitrogen and Water Status in Perennial Clover and Bunch Grass Cover Crop Systems of California's Central Valley[END_REF]. After calculation of several indices, their distribution was tested for normality and log 10 transformed when required. A repeated ANOVA was performed to test the effect of three treatments, the effect of different sampling dates and their interaction as the different measurements made on the same plots at different dates were not independent. We tested main effect of date and treatment, the additive effect and their interaction. The model best supported by the data was selected based on the Akaike Information Criterion (AIC; Burnham and Anderson 2002). Post-hoc tests were performed to test the effect of treatment or date on different variables. Statistical analyses were performed under R environment (R Development Core Team 2010) using the lme4, plotrix and multcomp packages.

Hypothesis 1: Inter-row management treatments as a gradient of disturbance and competition intensity

We first hypothesized that the three management practices represent a double gradient of disturbance and competition intensity, which acts as filters affecting species richness and abundance. We expected that tillage treatment would favor a small number of dominant species (low Shannon indices) whereas vegetation cover will favor a higher number of species, equally abundant (high Shannon indices). Our results showed that diversity indices varied among the three management practices, and the sampling date (Fig. 3). More precisely, spontaneous treatment showed the highest number of species with an average of 14 species per m 2 observed in all the sampling dates while tillage treatment harbours the lowest number of species and the highest variation across dates (Fig. 3a). Shannon diversity index was highest in the spontaneous treatment and lowest in the tillage treatment, indicating that in this treatment only a limited number of species were very abundant (Fig. 3b). High disturbance, corresponding to tillage treatment, resulted in less diverse communities dominated by a small number of species whereas an intermediate disturbance resulted in more diverse and equitable communities. On the contrary, there are some species that are very tolerant to all treatments e.g. Poa annua, Crepis sancta and Senecio vulgaris in April 2010 and Malva sylvestris in May 2011 which have also been shown to be among the most generalist weed species able to withstand a large range of management and ecological conditions in annual arable fields [START_REF] Fried | A Specialist-Generalist Classification of the French Arable Flora and Its Response to Changes in Agricultural Practice[END_REF]. Weed and cover crop biomass did not vary between the three treatments in April 2010 (Fig. 3c). Spontaneous and cover crop treatments did not present significant differences during the three dates of measurements, however it is important to notice that cover crop treatment presented a big variability across the different plots (certainly due to the establishment difficulties of the cover crop in the first year). In the tillage treatment, biomass was destroyed just before measurements in May and June.

Insert Figure 3 here Hypothesis 2: Functional structure of weed communities responds to management treatments

The second hypothesis was about species response traits to different management practices: that tillage treatment will favor species with traits corresponding to ruderal strategy (high growth rate, traits favoring resources acquisition), whereas cover crop will favor competitive species. To test this hypothesis we characterized weeds functional composition in the three inter-row treatments. We choose traits reflecting species morphology, phenology and reproduction (traits values were obtained in standardized databases: Leda, BiolFlor and Badoma). We then calculated community-weighted means (CWM; [START_REF] Garnier | Plant Functional Markers Capture Ecosystem Properties During Secondary Succession[END_REF] and Functional richness index which represents the amount of functional space filled by the community [START_REF] Villéger | New Multidimensional Functional Diversity Indices for a Multifaceted Framework in Functional Ecology[END_REF] for plant communities in the three treatments for all the sampling dates. Our results confirm the hypothesis that tillage treatment favored species with trait values associated to extensive exploitation of productivity-related resources and fast growth (especially high specific leaf area values). CWM of all the traits varied significantly among the three treatments. Species from the tillage treatment showed the lowest reproductive height values, the highest specific leaf area (SLA) values and late onset of flowering. The opposite pattern was found for species from the cover treatment (Fig. 4). This pattern can be explained in part if we consider the early onset of flowering observed in plants for the cover crop treatment: species in this treatment tend to flower and produce seeds earlier in season than Medicago plants. Additionally, species in the cover plant treatment showed the higher reproductive height values as a response to competition for light. The results of this study agree with the findings of [START_REF] Laliberté | Cascading Effects of Long-Term Land-Use Changes on Plant Traits and Ecosystem Functioning[END_REF][START_REF] Guerrero | Non-Linear Responses of Functional Diversity and Redundancy to Agricultural Intensification at the Field Scale in Mediterranean Arable Plant Communities[END_REF][START_REF] Flynn | Loss of Functional Diversity under Land Use Intensification across Multiple Taxa[END_REF]) who showed that the intensification of land use reduced functional diversity and redundancy. We also tested whether tillage treatment (highly disturbed habitat), act as a filter resulting in the convergence of traits within communities whereas plant cover (sown or spontaneous) vegetation will result to less similar species in the communities with large trait variability. We found that spontaneous vegetation treatment showed highest functional richness whereas in tillage treatment functional richness decreased even if species richness increased, thus implying functional convergence (Fig. 4d). Communities in spontaneous vegetation treatment showing high functional divergence, which indicates a high degree of niche differentiation, and thus low resource competition. Thus communities with high functional divergence may have increased ecosystem function, especially improvement of soil fertility and nutrient cycling, as a result of more efficient resource use (N. W. H. [START_REF] Mason | Functional Richness, Functional Evenness and Functional Divergence: The Primary Components of Functional Diversity[END_REF].

Insert Figure 4 here

Hypothesis 3: Species traits affect ecosystem properties

We hypothesized that different soil management practices in the vineyards will affect vine growth and performance. Although, spontaneous cover is supposed to have a higher impact on vine yield compared to tillage; it is expected that the effect of the legume cover crop is intermediate after two years, since competition with the vines is compensated by an increase in nitrogen supply and that the presence or the vigor of competitive weeds that may be present in spontaneous cover is reduced. However, spontaneous and tillage treatments presented significantly higher grapevine yields than the cover crop treatment around 4000 g/vine (which corresponds to about 12 t of grapes ha -1 according the density of vines per ha) in spontaneous and tillage treatments versus around 2500 g/ vine (corresponding to 7.5 t grapes ha -1 ) in the cover treatment) (Fig. 5a). This result can be explained by the non significant differences in biomass of spontaneous and cover crops and the higher functional trait divergence (especially of SLA, which corresponds to resource use). Predawn leaf water potential, a dynamic indicator of the water stress undertaken by the vine, shows that cover treatment always created higher water stress conditions for the vine throughout the summer (-0.64 MPa in late august versus -0.57 MPa and -0.58 for tillage and spontaneous treatment respectively) (Fig. 5b). Assimilable nitrogen in must was significantly higher at harvest at the tillage treatment (168 mg L -1 versus 80 mg L -1 and 105 mg L -1 for spontaneous and cover treatment respectively). For the latter two, the assimilable nitrogen content in must is below the threshold of 140 mg L -1 generally considered as nitrogen deficiency threshold [START_REF] Casalta | LWT -Food Science and Technology Comparison of Different Methods for the Determination of Assimilable Nitrogen in Grape Musts[END_REF]. Cover treatment based on legumes did not show any improvement in vine nitrogen nutrition even if there is a slight increase (Fig. 5c) probably because of the water stress created by the cover crop. In this case, the most limiting factor is water (Fig. 5b). [START_REF] Lavorel | How Fundamental Plant Functional Trait Relationships Scale-up to Trade-Offs and Synergies in Ecosystem Services[END_REF] proposed a framework based on alpine grasslands, differing in their management regime, corresponding to a gradient of management intensity: intensive management practices (like mowing and fertilization), favor species with traits values associated to high resources acquisition (high specific leaf surface for example), and thus influencing ecosystem processes and services (such as net primary productivity and rapid biochemical cycles). In our study, we found a positive relationship between specific leaf area CWM and vineyard yield (Fig. 6): communities dominated by species with high specific leaf area are linked to higher yield than communities dominated by species with low specific leaf area. This result, found for the first time in perennial crop systems like vineyards, allows testing directly the trait-service link and the hypothesis presented in Fig. 1b. This hypothesis should be tested on other ecosystem properties such as decomposition and mineralization as we hypothesize that intensive management practices, like tillage, acting like filter, for species traits favoring high growth rates, rapid nutrient mobilization and then rapid decomposition and mineralization. As a consequence, resources availability is high and vineyard yield increases. Our results did not clearly distinguish tillage treatment and spontaneous vegetation cover. There is a high variability in each treatment, which requires characterizing resources in more details for each community to interpret the results.

Insert Figure 6 here.

Conclusion and perspectives

In conclusion, both spontaneous and tillage treatments appeared acceptable as far as yield was maintained. The advantage of the tillage treatment on one hand was that it seemed efficiently able to limit weed growth (see biomass data in Fig. 3c) and consequently maintain both an adequate water status for the vine and a high level of assimilable nitrogen. On the other hand, spontaneous vegetation treatment can be chosen as a costless tradeoff for the winegrowers between improving soil properties, limiting mechanical work and maintaining vine production. This case study was the first demonstration of a direct relationship between functional traits and ecosystem services in perennial crop systems. This result confirms our initial hypothesis that the functional characterization of communities' responses to different management practices is a key issue to the management of inter-row communities, as traits with certain functional properties (e.g., ability to fix N 2 ) can be chosen in order to select or promote spontaneous species with those traits.

In this paper, we introduced a trait-based framework to assess vineyard inter-row soil management. As demonstrated in our case study, this framework has the potential to improve the understanding of weed community assembly and allow an adaptation of different soil management practices. According to this framework, it is essential to:

(i)
Characterize different management practices as disturbance and resource gradients in order to identify which traits may respond to these gradients;

(ii) Quantify resources availability and disturbance intensity; this will inform on which factors determine the abundance and species richness. For associated diversity, it is important to take the periodicity of disturbance turnover into account;

(iii) Identify and measure traits that are closely related to functions and processes across the gradients (response traits) as different functional traits are important for different services and ecosystem processes (see Table 3);

(iv) Measure the processes and services;

(v) Compare the diversity and ecosystem function(s)/service(s) of different management practices;

(vi) Test the linkages between traits and services (effect traits) and propose quantitative relationships. These relationships would make it possible to use traits to scale from individual plants and the communities they form to the ecosystem level function.

Given the results obtained, different "ideotypes", i.e. species with required traits, providing several services, could be proposed considering both grapegrower's objectives. The choice of those "ideotypes" will contribute to design more sustainable grapevine systems. More precisely based on Table 3 we propose species with:

(i) High specific leaf area and low dry matter content as well as N fixing species which will improve soil fertility and nutrient cycling;

(ii) High root density in order to support water regulation;

(iii) Rosette and herbaceous species with high growth rate which will support soil stability.

(

  Vitis vinifera L. cv.Shiraz) were planted in 2002, in rows oriented NW-SE at a density of 3333 stocks per hectare (2.5 m × 1.2 m). Three treatments were designed to create a gradient of soil resources (water and nitrogen): (a) A first treatment was obtained by sowing a mix of annual medics (Medicago truncatula, M. rigidula,M. polymorpha) in the inter-row during autumn 2009 (cover crop treatment hereafter); (b) A second treatment with bare soil was obtained by mechanical weeding in the inter-row with three operations in spring (in April, May and June in 2010 and in March, April and June in 2011), (tillage treatment hereafter); (c) permanent natural plant coverage between rows (spontaneous cover treatment) mowed twice a year. There was no fertilization or irrigation in these treatments. Treatments were applied as strips. Cover crop and Tillage treatments were composed of 185 vine stocks (37 vinestocks per row and 5 rows) whereas Spontaneous cover treatment composed of 74 vine stocks (37 vinestocks per row and 2 rows).

designing the analysis and reviewed the manuscript. Cyrille Violle is a plant ecologist working at the Centre d'Ecologie Fonctionelle et Evolutive (UMR CEFE 5175). Contribution: helped with the statistical analyses and reviewed the manuscript.