Zhen Shen

Claude Monnet

Borja Cascales-Miñana

Yiming Gong
email: ymgong@cug.edu.cn

Xianghong Dong

David M Kroeck

Thomas Servais

Diversity dynamics of Devonian terrestrial palynofloras from China: Regional and global significance

Keywords: Miospores, Palaeobiodiversity, China, Devonian, Climate change

The microfossil-based pattern of the Devonian land plants of China is revised and discussed based on a newly comprehensive dataset. Such dataset compiles the chronostratigraphical distribution of 1677 species belonging to190 genera of spores and pollen from the primary literature, which recovers the fossil history of Chinese terrestrial palynofloras. From this, we describe the patterns and biodiversity dynamics using both range-based and occurrence-based data to illustrate the main fluctuations of Devonian taxonomic richness, including rarefaction for filtering out uneven sampling. Results show that the apparent terrestrial palynofloral diversity of China increases progressively from the early to mid-Devonian, with a genuine Givetian peak followed by a plateau persisting during the Late Devonian. Results further suggest that sampling effects may strongly influence the perception of biodiversity trends of China, as well as that the observed Late Devonian taxonomic diversification may have been greatly overestimated. Compiled evidence is discussed on the light of the global evolution of marine-terrestrial ecosystems. We hypothesize that the rise of Devonian floras may have played a remarkable role in an oceanic oxygenation event during this Period.

Introduction

The approximately 60 million years long Devonian Period is characterized by major changes in both terrestrial and marine biospheres [START_REF] Algeo | Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events[END_REF][START_REF] Cohen | The ICS International Chronostratigraphical Chart[END_REF]. Such changes were triggered possibly by the appearance and the diversification of earliest forests, which has been considered as the 'greening of Earth surface' [START_REF] Giesen | Reconstruction and growth of the early tree Calamophyton (Pseudosporochnales, Cladoxylopsida) based on exceptionally complete specimens from Lindlar, Germany (Mid-Devonian): organic connection of Calamophyton branches and Duisbergia trunks[END_REF], and by the blooms of nektonic animals (e.g. freeswimming cephalopods) in the oceans, which have been related to the 'mid-Palaeozoic predator revolution' [START_REF] Signor | The mid-Paleozoic precursor to the Mesozoic marine revolution[END_REF][START_REF] Brett | Durophagous predation in Paleozoic marine benthic assemblages[END_REF] or the 'Devonian Nekton Revolution' [START_REF] Klug | The Devonian nekton revolution[END_REF].

The Devonian Period was also crucial time of plant evolution, with plant palynomorph diversities (see e.g. Fig. 1) increasing steadily during the entire Devonian (see e.g. Traverse, 2007 and references therein). The land plant microfossils, which are much more abundant and widespread than land plant megafossils, are generally found not only in terrestrial deposits but also in near shore marine strata, and there, mixed with other palynomorphs and also with marine macrofossils, allowing accurate dating (e.g. [START_REF] Streel | Late Frasnian-Famennian climates based on palynomorph analyses and the question of the Late Devonian glaciations[END_REF]. This evidence has proven to be extremely useful in solving palaeogeographical, palaeoenvironmental, and biostratigraphical questions, particularly in Palaeozoic strata (e.g. [START_REF] Streel | Late Frasnian-Famennian climates based on palynomorph analyses and the question of the Late Devonian glaciations[END_REF]. Although the first paper concerning palynology in China was already published in the 1930s [START_REF] Ding | Method in pollen analysis and its application[END_REF], more intense palynological investigations were not performed before the 1950s [START_REF] Hsü | Devonian spores from Yunnan. China[END_REF][START_REF] Wang | Progress and prospect of studies on palynology in China[END_REF]. Since then, especially after the early 1970s, more than 100 scientific articles dealing with Devonian palynomorphs in China have been published. It should be noted that most results on Devonian microfossils from China were published in Chinese, with only very few papers submitted to international journals. The period between the 1970s to the 1990s was the most active interval for Devonian palynological research in China (Fig. 2).

Although the taxonomic investigation and/or the biostratigraphical use of Devonian palynolomorphs from China were extensively reported, very few studies summarized systematically such records (e.g. [START_REF] Gao | Devonian spore assemblages of China[END_REF][START_REF] Xiong | Diversity Dynamics of Silurian-Early Carboniferous Land Plants in South China[END_REF][START_REF] Ouyang | The Late Paleozoic spore and pollen of China[END_REF].

In additions, discussions of the relationships between plant megafossil and/or microfossil diversity trajectories as well as the biotic-abiotic factors remain rare. More recently, a monograph on Late Palaeozoic spores and pollen from China has been published by [START_REF] Ouyang | The Late Paleozoic spore and pollen of China[END_REF]. This latter work is a compilation of the taxonomic information extracted from the literature and it provides an essential synthesis for Upper Palaeozoic palynological research of China. Although a number of papers have been published in recent years concerning the plant diversity dynamics of Devonian megafossils and spores [START_REF] Knoll | Character Diversification and Patterns of Evolution in Early Vascular Plants[END_REF][START_REF] Raymond | Laurussian Land-Plant Diversity During the Silurian and Devonian: Mass Extinction, Sampling Bias, or Both?[END_REF][START_REF] Wang | The evolution of Paleozoic vascular land plant diversity of South China[END_REF][START_REF] Gutak | Diversity and richness of the Devonian terrestrial plants in the Southeastern Mountainous Altay (Southern Siberia): Regional versus global patterns[END_REF][START_REF] Xiong | Diversity Dynamics of Silurian-Early Carboniferous Land Plants in South China[END_REF], there are only few studies that have corrected the effects of sampling bias.

Furthermore, a debate of the evolution of Devonian terrestrial biodiversities is still ongoing (see e.g. Cascales-Miñana, 2016, references included).

In addition to a detailed overview on the progress of Chinese studies on Devonian terrestrial palynofloras, the present work is mainly focused on the plant microfossilbesed diversity patterns via a sample-based rarefaction analysis. The new compilation of terrestrial palynofloras presented herein, contains all spore and pollen data recorded between the latest Silurian and the earliest Carboniferous from different regions of China. This survey has yielded an inventory of 84 selected publications that demonstrated sufficient chronostratigraphical information to calibrate the occurrences of terrestrial palynofloral at the stage level, in order to identify the main biodiversity changes and outline their interactions with biotic and abiotic factors.

The latest Silurian-earliest Carboniferous terrestrial palynofloras of China

Currently, China is an amalgam of terranes (Fig. 3a) that during the Devonian were spreaded across the Palaeo-Asian Ocean, including a series of volcanic arcs that were intermittently linked through Siberia and Kazakhstan [START_REF] Xiao | The western Central Asian Orogenic Belt: A window to accretionary orogenesis and continental growth[END_REF].

Many Devonian outcrops are widely exposed in South China, NW China, and NE China, but not in the North China Platform that was uplifted between the Middle Ordovician and the Early Carboniferous, with only scattered marine records in its southern margin [START_REF] Ma | The Devonian System of China, with a discussion on sea-level change in South China[END_REF]. On the basis of tectonic, stratigraphical and palaeontological informations, the following regions of China can be recognized during the Devonian (Fig. 3b; [START_REF] Liao | Devonian Biostratigraphy of China[END_REF] : (1) Junggar region (Kazakhstan plate), (2) Hinggan region (Songhua River-Bureja plate), (3) Tarim region (Tarim plate), (4) Qilian-Qaidam region (Qilian-Qaidam plate), (5) Qinling region, (6) South China region (South China plate), (7) Western Yunnan region (Sibumasu plate) and (8) Himalaya region (India plate). From all these areas, South China has provided the large majority of published studies on Devonian palynomorphs (Appendix A).

Figure 4 depicts the Devonian stratigraphical framework of selected areas of China. In addition to the 84 references (Fig. 5) used for the miospore diversity analysis, other references without detailed statistical significance are also listed in the present study. These publications provide a mass of supplementary information, from numerous additional fossil localities (Bharadwoj et al., 1973;Lu, 1980bLu, , 1994b;;[START_REF] Gao | Devonian spore assemblages of China[END_REF][START_REF] Gao | Late Devonian and Early Carboniferous Miospore Zonations and the boundary of Devonian-Carboniferous in China[END_REF]Gao, , 1988cGao, , 1988dGao, , 1988e, 1989bGao, , 1991bGao, , 1991cGao, , 1999b;;[START_REF] Ye | On the occurrence of spore assemblages from the Shujiaba region of Tianshui County, Gansu and their stratigraphical significance[END_REF][START_REF] Gao | The discovery of the microfossils in Xinyang group, Henan, and the geological significance[END_REF][START_REF] Ouyang | Palynology of Devonian-Carboniferous transition sequences of Jiangsu, E. China[END_REF][START_REF] Pei | The discovery of the Devonian-Carboniferous spores in Nanzhao, Henan[END_REF][START_REF] Zhu | Devonian-Carboniferous miospore assemblages from the Tarim basin and their biostratigraphical implications[END_REF]Zhu and Zhao, 1998;Zhu et al., 1999;[START_REF] Ouyang | Succession of Late Palaeozoic palynological assemblages in Jiangsu[END_REF][START_REF] Su | The features and time-discussion of the spore assemblages from Shujiaba formation in west Qinling area[END_REF][START_REF] Wang | A new lycopsid megaspore cone from the Upper Devonian of Chaohu, China[END_REF][START_REF] Zhang | Features of the strata for Devonian Queershan group in Hongshishan area of Beishan's northern belt, Gansu[END_REF][START_REF] Zhu | Some specific Devonian spores from China, Saudi Arabia and Australia[END_REF]. South central Guangxi [START_REF] Cheng | China stratigraphy, Devonian[END_REF][START_REF] Pan | The Devonian continental facies of South China[END_REF]; Eastern Yunnan (Xu andGao, 1991, 1994;[START_REF] Wang | Lower Devonian miospores from Gumu in the Wenshan District, southeastern Yunnan[END_REF]; South of Jiangsu [START_REF] Cheng | China stratigraphy, Devonian[END_REF]; Western Hubei and Northeast Hunan [START_REF] Pan | The Devonian continental facies of South China[END_REF][START_REF] Feng | Chapter two: The Devonian[END_REF][START_REF] Gao | The biostratigraphy of The Three Gorges area, 3, the fascicle of the Late Palaeozoic[END_REF]; Western Zhejiang [START_REF] Cheng | China stratigraphy, Devonian[END_REF]; Southern Guizhou [START_REF] Pan | The Devonian continental facies of South China[END_REF][START_REF] Gao | The Early-Middle Dovenian spores and their stratigraphical significance in Dushan and Duyun, Guizhou[END_REF]; Western Yunnan (Gao, 1999a); Central Hunan [START_REF] Wang | Miospore assemblages from the Shaodong and Mengkung'ao Formations at Xikuangshan, central Hunan with discussion on Devonian-Carboniferous boundary[END_REF]Geology and mineral bureau of Hunan, 1988); Jiangxi [START_REF] Pan | The Devonian continental facies of South China[END_REF][START_REF] Wen | Devonian-Carboniferous miospore assemblages from Xiaomu Section of Quannan, Jiangxi, China[END_REF]; Heilongjiang [START_REF] Ouyang | Microfossils from the Devonian Heitai formation of Mishan County, Heilongjiang Province[END_REF]; Western Qinling [START_REF] Cao | Lithostratigraphy. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of Ministry of geology and mineral resources[END_REF][START_REF] Su | The features and time-discussion of the spore assemblages from Shujiaba formation in west Qinling area[END_REF]; Tarim, Xinjiang [START_REF] Zhu | On the age of spore assemblage from Donghe sandstone in well Cao-2 of North Tarim basin[END_REF][START_REF] Zhu | Discovery of Late Devonian spores of the Bachu formation from the South of Xinjiang, and their stratigraphical significance. The "Nine Five" anthology of important achievements in national geological science and technology[END_REF]; Junggar, Xinjiang [START_REF] Gong | Paleozoic Stratigraphic Regionalization and Paleogeographic Evolution in Western Junggar, Northwestern China[END_REF]; Geology and mineral bureau of Xinjiang Uygur autonomous region, 1982); Inner Mongolia (Gao, 1996a); Nyalam, Tibet (Gao, 1983a[START_REF] Gao | Late Devonian and Early Carboniferous acritarchs from Nyalam County, Xizang (Tibet), China[END_REF]; Longhuashan, Sichuan [START_REF] Hou | Chengdu Institute of Geology and Mineral Resources, CAGS, Institution of Geology. Stratigraphy, palaeontology and sedimental facies of Devonian in Longmenshan, Sichuan. Beijing[END_REF]. Si.: Silurian; Pri.: Pridoli Series (Pridolian stage).

Pridoli (Late Silurian)

Six papers concern spore taxa from the Pridolian stage (latest Silurian Pridoli Series) [START_REF] Gao | Late Silurian-Early Devonian spores and acritarchs from west Junggar[END_REF](Gao, , 1996b;;[START_REF] Gao | Late Silurian and Devonian spores from west Qinling MTS., China. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of ministry of geology and mineral resources[END_REF][START_REF] Fang | New advance in the study of the Silurian-Devonian boundary in Qujing, East Yunnan[END_REF][START_REF] Tian | The Late Silurian-Middle Devonian miospore biostratigraphy from eastern Yunnan[END_REF][START_REF] Tian | Late Silurian to Early Devonian Palynomorphs from Qujing, Yunnan, Southwest China[END_REF]. In Junggar, [START_REF] Gao | Late Silurian-Early Devonian spores and acritarchs from west Junggar[END_REF] reported Late Silurian-Early Devonian miospores, together with few acritarchs and chitinozoans from the Shaerbuerti mountain, Western Junggar (Fig. 3b, location 12). Four miospore zones were established on the basis of the distribution regularities and evolutionary features. In ascending order, they are Synorisporites dittonensis-Apiculiretusispora spicula (DS);

Emphanisporites micronatus-Streelispora newportensis (MN); Chelinospora cassicula-Perotriletes subitus (CS); Grandispora sp.-Apiculatasporites microconus (CM), the Silurian-Devonian boundary (SDB) being placed between the DS and MN miospore zones. In western Yunnan, Gao (1996b) described sixty-five spore and acritarch species from Silurian-Early Devonian levels from the Niushiping, Xiangyangsi, and Wangjiacun formations in Shidian, west Yunnan (Fig. 3b, location 4). Three spore assemblage zones were established in ascending order: Apiculiretusispora spicula-Emphanisporites neglectus (SN, Late Silurian),

Synorisporites verrucatus-Streelispora newportensis (VN, Early Devonian), and

Breconisporites breconensis-Cymbosporites dittonensis (BD, Early Devonian). In western Qinling, [START_REF] Gao | Late Silurian and Devonian spores from west Qinling MTS., China. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of ministry of geology and mineral resources[END_REF] documented the first time the spore assemblages from the Late Silurian-Devonian time interval, including 47 spore genera and a few acritarchs and scolecodonts from Diebu, Gansu and Ruoergai, Sichuan. In eastern Yunnan (Fig. 3b, location 2), [START_REF] Fang | New advance in the study of the Silurian-Devonian boundary in Qujing, East Yunnan[END_REF] identified some spore taxa from the Yulongsi Formation and discussed the geological age of this formation from Qujing, Yunnan. The authors argued that the SDB should be at the top of the Yulongsi Formation or at the base of the Xiaxishancun Formation. Subsequently, [START_REF] Tian | The Late Silurian-Middle Devonian miospore biostratigraphy from eastern Yunnan[END_REF] and [START_REF] Tian | Late Silurian to Early Devonian Palynomorphs from Qujing, Yunnan, Southwest China[END_REF] reported the new discoveries of the Late Silurian-Middle Devonian interval from eastern Yunnan. Four spore assemblage zones from the Late Silurian to the Early Devonian were proposed in ascending stratigraphical order: Ambitisporites dilutus-Apiculiretusispora synorea (DS; late Ludfordian to early Pridolian); Synorisporites verrucatus-Apiculiretusispora plicata (VP; Pridolian); Apiculiretusispora minuta-Leiotriletes ornatus (MO; Lochkovian), and Verrucosisporites polygonalis-Dibolisporites wetteldorfensis (PW; Pragian) [START_REF] Tian | Late Silurian to Early Devonian Palynomorphs from Qujing, Yunnan, Southwest China[END_REF].

Early Devonian

There are a total of 22 papers discussing Early Devonian spores from China (e.g. [START_REF] Gao | The Early-Middle Dovenian spores and their stratigraphical significance in Dushan and Duyun, Guizhou[END_REF][START_REF] Lu | The Early Devonian spore assemblage from the Xujiachong Formation at Cuifengshan, in Qujing of Yunnan[END_REF][START_REF] Gao | The Early Devonian spores and acritarchs in Liujing, Guangxi[END_REF]Gao, , 1983b[START_REF] Gao | Early Devonian spores and acritarches from the Guijiatun Formation of Qujing, Yunnan[END_REF]Gao, , 1988a[START_REF] Gao | Late Silurian-Early Devonian spores and acritarchs from west Junggar[END_REF]Gao, , 1996aGao, , 1996b[START_REF] Gao | Acritarchs from Lower Devonian Ganxi and Xiejiawan formations in Longmenshan mountain, Sichuan[END_REF][START_REF] Pan | The Devonian continental facies of South China[END_REF]Lu, 1980a;[START_REF] Gao | Late Silurian and Devonian spores from west Qinling MTS., China. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of ministry of geology and mineral resources[END_REF][START_REF] Gao | Early Devonian miospore assemblage from the Yuankou Formation in southern Hunan and its stratigraphical significance[END_REF][START_REF] Fang | New advance in the study of the Silurian-Devonian boundary in Qujing, East Yunnan[END_REF][START_REF] Wang | Lower Devonian miospores from Gumu in the Wenshan District, southeastern Yunnan[END_REF]Tian andZhu, 2005, 2009;[START_REF] Huang | The first exploration of the Lower Devonian Spore Assemblages in Guixi formation from Longmen Mountains, Sichuan Province[END_REF][START_REF] Tian | Late Silurian to Early Devonian Palynomorphs from Qujing, Yunnan, Southwest China[END_REF][START_REF] Wellman | Spore assemblages from the Lower Devonian Xujiachong Formation from Qujing, Yunnan, China[END_REF][START_REF] Huang | Lower and Middle Devonian Spore Assemblages from Longmen Mountains, Sichuan Province[END_REF]. The records that have been mentioned above are no longer discussed in detail in the following paragraphs.

South China region

A total of 17 publications deal with Early Devonian miospore assemblages. The research area concentrates on the Guizhou, Yunnan, Guangxi, Sichuan, and Hunan provinces. In Guizhou, two papers were published: [START_REF] Gao | The Early-Middle Dovenian spores and their stratigraphical significance in Dushan and Duyun, Guizhou[END_REF] and Gao (1983b) studied the Lower to the Middle Devonian spore assemblages from southern Guizhou (Fig. 3b, locations 8 and 27), and distinguished four assemblage zones. As a result, the Danlin Formation was considered Pragian-Emsian in age, and the Longdongshui Formation was attributed to the early Middle Devonian.

The Lower Devonian strata of eastern Yunnan have received wide attention for their non-marine to marine sediments. The studied strata dealing with Lower Devonian spore assemblages are as follows: Xujiachong Formation [START_REF] Lu | The Early Devonian spore assemblage from the Xujiachong Formation at Cuifengshan, in Qujing of Yunnan[END_REF]Lu, 1980a;Gao, 1983b;[START_REF] Wellman | Spore assemblages from the Lower Devonian Xujiachong Formation from Qujing, Yunnan, China[END_REF], Cuifengshan Group [START_REF] Pan | The Devonian continental facies of South China[END_REF], Guijiatun Formation [START_REF] Gao | Early Devonian spores and acritarches from the Guijiatun Formation of Qujing, Yunnan[END_REF], Xiaxishancun Formation [START_REF] Fang | New advance in the study of the Silurian-Devonian boundary in Qujing, East Yunnan[END_REF]Gao, 1983b), and Pojiao Formation (Gao, 1983b). [START_REF] Wang | Lower Devonian miospores from Gumu in the Wenshan District, southeastern Yunnan[END_REF] studied the spore taxa from Wenshan, Yunnan (Fig. 3b, location 10) and established two palynomorph assemblage zones in the Posongchong (Pragian) and Pojiao formations (Emsian), i.e., Apiculiretusispora plicata-Dictyotriletes emsiensis (PE), and Dibolisporites eifeliensis-Camarozonotriletes sextantii (ES), respectively. [START_REF] Tian | Devonian miospore biostratigraphy of the Longhuashan and Xichong Formations in Zhanyi of Yunnan[END_REF] investigated the spore assemblages and the biozones from the Longhuashan (Xujiachong), and Xichong formations in Qujing, Yunnan, with two spore assemblage zones proposed in ascending order, i.e., Retusotriletes rotundus-Apiculiretusispora plicata (RP; Longhuashan Formation), and Archaeozonotriletes variabilis-Cymbosporites magnificus (VM; Xichong Formation). [START_REF] Tian | Devonian miospore biostratigraphy of the Longhuashan and Xichong Formations in Zhanyi of Yunnan[END_REF] placed the Longhuashan Formation between the middle Pragian and the lower Emsian, while the upper member of the Xichong Formation was thought to belong to the late Givetian to early Frasnian interval. Based on the dispersed spore assemblages recovered from the Xujiachong Formation in Qujing, Yunnan, [START_REF] Wellman | Spore assemblages from the Lower Devonian Xujiachong Formation from Qujing, Yunnan, China[END_REF] discussed the age, palaeoenvironment, as well as the biotas, and considered that the assemblages approximately correspond to the early Pragian-Emsian Verrucosisporites polygonalis-Dictyotriletes emsiensis assemblage zone of the Old Red Sandstone continent and adjacent regions [START_REF] Richardson | Silurian and Devonia spore zones of the Old Red Sandstone continent and adjacent regions[END_REF].

In the Longmenshan area, Sichuan (Fig. 3b, location 1), three studies have mentioned Early Devonian spores. Gao (1988a) summarized the characteristics of a total of 148 species (including 32 new species and seven new combinations) assigned to 35 genera from the Pingyipu Group and the Bailiuping Formation. [START_REF] Huang | The first exploration of the Lower Devonian Spore Assemblages in Guixi formation from Longmen Mountains, Sichuan Province[END_REF] explored the spores records from the Lower Devonian Guixi Formation and suggested that they might belong to the 'Gedinnian' establishing the Acinosporites In addition to the areas discussed above, palynomorphs were also reported from Hunan and Guangxi. In southern Hunan (Fig. 3b, location 9), [START_REF] Gao | Early Devonian miospore assemblage from the Yuankou Formation in southern Hunan and its stratigraphical significance[END_REF] examined the spore assemblages from the Lower Devonian Yuankou Formation, in which 22 genera and 44 species and variations were figured in a stratigraphical column. The authors believed that the age of the assemblage would be 'Siegenian. ' In Guangxi (Fig. 3b,location 7), [START_REF] Gao | The Early Devonian spores and acritarchs in Liujing, Guangxi[END_REF] documented the spore assemblages and a small number of acritarchs from Hengxian County, and compared the spore composition to those of European and north African countries. Finally, [START_REF] Gao | The Early Devonian spores and acritarchs in Liujing, Guangxi[END_REF] determined the age of the spore assemblages based on other fossil groups, such as brachiopods, coral reefs, and fish.

Western Yunnan region

In western Yunnan (Fig. 3b, location 4), only a single report has been published by Gao (1996b)

Junggar region

See above.

Hinggan region

Only a single paper has been published from this region. Gao (1996a) studied the palynomorph assemblages including spores, acritarchs, and scolecodonts from the Baruntehua Formation in Wuzhumunqi Qi, Inner Mongolia. He considered the palynomorphs of the lower part of the Baruntehua Formation to be very similar to those from the 'Gedinnian' of Europe and North America.

Qinling region

Gao and [START_REF] Gao | Late Silurian and Devonian spores from west Qinling MTS., China. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of ministry of geology and mineral resources[END_REF]

Middle Devonian

21 references so far have recovered spores of the Middle Devonian in China (e.g. [START_REF] Gao | The Early-Middle Dovenian spores and their stratigraphical significance in Dushan and Duyun, Guizhou[END_REF][START_REF] Lu | Devonian megaspores from the Zhanyi district, E. Yunnna[END_REF]Lu, 1980a[START_REF] Lu | Middle Devonian microflora from Haikou Formation at Shijiaopo in Zhanyi of Yunnan, China[END_REF]Lu, , 1997b;;Gao, 1983bGao, , 1989a;;[START_REF] Gao | The biostratigraphy of The Three Gorges area, 3, the fascicle of the Late Palaeozoic[END_REF][START_REF] Ouyang | Microfossils from the Devonian Heitai formation of Mishan County, Heilongjiang Province[END_REF][START_REF] Gao | Late Silurian and Devonian spores from west Qinling MTS., China. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of ministry of geology and mineral resources[END_REF]Xu andGao, 1991, 1994;Tian andZhu, 2005, 2009;[START_REF] Gao | Discovery of Devonian spores in the Huoshenmiao Formation of the Erlangping Group in the Xixia area, Henan, China[END_REF][START_REF] Gao | Discovery of the Middle Devonian spores from Baimianxia Formaion of Sanhuashi Group, Xixiang-Shiquan region, South Qinling, China and its geological significance[END_REF][START_REF] Zhu | Biostratigraphic and paleogeographic significance of a palynological assemblage from the Middle Devonian Ulusubasite Formation, eastern Junggar Basin, Xinjiang, China[END_REF][START_REF] Xu | Mid Devonian megaspores from Yunnan and North Xinjiang, China: Their palaeogeographical and palaeoenvironmental significances[END_REF][START_REF] Xu | Devonian spores from an intra-oceanic volcanic arc, West Junggar (Xinjiang, China) and the palaeogeographical significance of the associated fossil plant beds[END_REF][START_REF] Huang | Lower and Middle Devonian Spore Assemblages from Longmen Mountains, Sichuan Province[END_REF][START_REF] Marshall | Provincial Devonian spores from South China, Saudi Arabia and Australia[END_REF].

South China region

The research on spore taxa of the Middle Devonian in South China is mainly concentrated in eastern Yunnan, from the counties of Luquan [START_REF] Marshall | Provincial Devonian spores from South China, Saudi Arabia and Australia[END_REF] and Zhanyi [START_REF] Lu | Devonian megaspores from the Zhanyi district, E. Yunnna[END_REF][START_REF] Lu | Middle Devonian microflora from Haikou Formation at Shijiaopo in Zhanyi of Yunnan, China[END_REF]. In eastern Yunnan, Xu andGao (1991, 1994) The Middle Devonian miospores are known also in other regions, for instance, from the Hunan and Hubei provinces. The spore assemblages from the Yuntaiguan, Huangjiadeng (Fig. 3b, locations 16 and 28), and Tizikou formations (Fig. 3b, locations 16 and 28) were discussed by [START_REF] Gao | The biostratigraphy of The Three Gorges area, 3, the fascicle of the Late Palaeozoic[END_REF] and Gao (1989a). The Yuntaiguan Formation (Fig. 3b, location 16) was later attributed to the Givetian by Gao (1989a).

Qinling

Only two papers have been published from this area. In addition to [START_REF] Gao | Late Silurian and Devonian spores from west Qinling MTS., China. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of ministry of geology and mineral resources[END_REF] (see above), [START_REF] Gao | Discovery of the Middle Devonian spores from Baimianxia Formaion of Sanhuashi Group, Xixiang-Shiquan region, South Qinling, China and its geological significance[END_REF] discussed the age of the spores that he collected from the Sanhuashi and Xixiang groups, Shaanxi Province (Fig. 3b, location 14). The fossil assemblages of possible Middle Devonian age can be roughly correlated with the spores in regions of South China, Europe, and North America.

Junggar

In addition to the literature mentioned above (e.g. [START_REF] Xu | Devonian spores from an intra-oceanic volcanic arc, West Junggar (Xinjiang, China) and the palaeogeographical significance of the associated fossil plant beds[END_REF], [START_REF] Xu | Mid Devonian megaspores from Yunnan and North Xinjiang, China: Their palaeogeographical and palaeoenvironmental significances[END_REF] reported Middle Devonian megaspores collected from both northern Xinjiang (Fig. By recording the newly collected 36 genera and 83 spore species from the Hujieersite Formation in Hoboksar (see above), and from western Junggar, Xinjiang, Lu (1997b) indicated that the spore assemblages belonged to Givetian. More recently, acritarch and miospore assemblages from the Ulusubasite Formation (Eifelian) in eastern Junggar (Fig. 3b, locality 50) were described and their biostratigraphical and palaeogeographical implications were discussed by [START_REF] Zhu | Biostratigraphic and paleogeographic significance of a palynological assemblage from the Middle Devonian Ulusubasite Formation, eastern Junggar Basin, Xinjiang, China[END_REF].

Hinggan region

Ouyang (1984) studied the spore microfloras collected from the upper part of the Heitai Formation in Mishan County (Fig. 3b, location 18), Heilongjiang, and considered that the upper part of this formation belonged to the Givetian, while the lower part might be Eifelian in age.

Late Devonian-Tournaisian (earliest Carboniferous)

The publications concerning the Late Devonian-Early Carboniferous interval are the most abundant, accounting for more than half of the total of all investigations. 52 reports of Chinese terrestrial palynofloras have been published [START_REF] Lu | Upper Devonian (Frasnian) sporopollen assemblage from the Damaidi area of Dukou, Sichuan Province[END_REF](Lu, , 1994a[START_REF] Lu | Miospores from Shaodong Member at Jieling Section of Hunan, China and their geological age[END_REF](Lu, , 1997a[START_REF] Lu | On the miospore assemblages of the heishantou formation at aherbruckomha in Horboksar, Xinjiang, with additional reference to the transition stratum from Devonian to Carboniferous[END_REF][START_REF] Hou | Some spore assemblages of the Devonian-Carboniferous transition from Xikuangshan District, central Hunan[END_REF][START_REF] Gao | Lower Carboniferous spore assemblage from the Qianheishan formation of Jingyuan County, Kansu and its age[END_REF]Gao, , 1983aGao, , 1985Gao, , 1988bGao, , 1990aGao, , 1990bGao, , 1991a[START_REF] Gao | Palynostratigraphy at the Devonian-Carboniferous boundary in West Hubei and northwest Hunan Provinces[END_REF][START_REF] Gao | The Late Devonian-Early Carboniferous miospore zonation in the lower Yangtze Valley, China and the Devonian-Carboniferous boundary[END_REF][START_REF] Gao | The biostratigraphy of The Three Gorges area, 3, the fascicle of the Late Palaeozoic[END_REF][START_REF] Liu | Conchostracans and spores of Upper Devonian Huangjiadeng Formation in Hubei Province[END_REF]Chen andOuyang, 1985, 1987;[START_REF] Gao | Late Silurian and Devonian spores from west Qinling MTS., China. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of ministry of geology and mineral resources[END_REF][START_REF] Li | Cishan Formation-Early Aikuanian strata in the Nanjing region[END_REF]Ouyang andChen, 1987a, 1987b;[START_REF] Wang | The Devonian-Carboniferous boundary of benthonic facies in central Hunan[END_REF][START_REF] Yan | Lower Carboniferous in the Lower Yangtze Region[END_REF][START_REF] Yang | Spores[END_REF][START_REF] Cai | The Devonian biostratigraphy in Jiangsu, the Lower Yangtze Platform[END_REF][START_REF] Lu | Upper Devonian acritarchs and spores from the Hongguleleng Formation, Hefeng district in Xinjiang, China[END_REF][START_REF] Gao | The discovery of early Early Carboniferous miospore in northern Tarim and its geological significance[END_REF]Xu andGao, 1991, 1994;[START_REF] Gao | Carboniferous sporopollen from Qinghai and its stratigraphic significance[END_REF][START_REF] Yan | The microflora of the Tangjiawu and Xihu Formations in Zhejiang and their stratigraphical division and correlation[END_REF][START_REF] Fang | A New Advancement of the Devonian-Carboniferous boundary in Central Hunan Province, China[END_REF][START_REF] He | Spore assemblages from Devonian-Carboniferous transitional beds of Hsihu Formation, Fuyang, W. Zhejiang[END_REF][START_REF] Wen | Devonian-Carboniferous miospore assemblages from Xiaomu Section of Quannan, Jiangxi, China[END_REF][START_REF] Gao | Discovery and significance of Retispora lepidophyta from Qizilafu group, Yecheng County, Xinjiang[END_REF][START_REF] Steemans | Retizonomonoletes hunanensis Fang et al., 1993 and the lepidophyta morphon[END_REF][START_REF] Wang | Miospore assemblages from the Shaodong and Mengkung'ao Formations at Xikuangshan, central Hunan with discussion on Devonian-Carboniferous boundary[END_REF][START_REF] Zhu | Discovery of Late Devonian spores from the Southwestern margin of Tarim basin and their significance[END_REF]Zhu, , 1999aZhu, , 1999b[START_REF] Zhu | Upper Devonian spores from the North Tarim Basin, NW China[END_REF]Zhu et al., 1998;[START_REF] Yang | Palynological study of the Devonian-Carboniferous boundary in the vicinity of the International Auxiliary Stratotype Section, Guilin, China[END_REF][START_REF] Gao | Late Devonian of Sporopollen Bacan well 1 in West Tarim Basin and its stratigraphic significance[END_REF]Zhu and Zhao, 1999;[START_REF] Yang | Stratigraphic and phytogeographic palynology of late Paleozoic sediments in western Yunnan, China[END_REF][START_REF] Zhu | Discovery of Late Devonian spores of the Bachu formation from the South of Xinjiang, and their stratigraphical significance. The "Nine Five" anthology of important achievements in national geological science and technology[END_REF][START_REF] Li | Devonian plants and stratum in Wuhan, Hubei Province, China[END_REF][START_REF] Ouyang | The study of Carboniferous -Permian palynofloras in N. Xinjiang, NW China[END_REF][START_REF] Yang | The discovery of lower Carboniferous miospores assemblages from a borehole in the Binhai district, north Jiangsu[END_REF][START_REF] Tian | Devonian miospore biostratigraphy of the Longhuashan and Xichong Formations in Zhanyi of Yunnan[END_REF][START_REF] Gao | Discovery of spores from the epimetamorphic rocks in southern Anhui and its geological significance[END_REF][START_REF] Xu | Devonian spores from an intra-oceanic volcanic arc, West Junggar (Xinjiang, China) and the palaeogeographical significance of the associated fossil plant beds[END_REF].

South China

The large majority of the studies, with more than 50% of the literature on Devonian land plant microfossils, are focused on the assemblages from South China.

In addition to the above-mentioned publications, that documented Lower and/or Middle Devonian sections, other extended also into the Upper Devonian [START_REF] Gao | The biostratigraphy of The Three Gorges area, 3, the fascicle of the Late Palaeozoic[END_REF]Xu andGao, 1991, 1994;[START_REF] Tian | Devonian miospore biostratigraphy of the Longhuashan and Xichong Formations in Zhanyi of Yunnan[END_REF][START_REF] Xu | Devonian spores from an intra-oceanic volcanic arc, West Junggar (Xinjiang, China) and the palaeogeographical significance of the associated fossil plant beds[END_REF], with a total of more than thirty references reporting the Late Devonian-Early Carboniferous palynofloras of South China.

In Jiangsu, the occurrences of spores (including miospores and megaspores) were reported by Chen andOuyang (1985, 1987) and Ouyang andChen (1987a, 1987b).

Other papers covering the spores of this region include [START_REF] Yan | Lower Carboniferous in the Lower Yangtze Region[END_REF], [START_REF] Cai | The Devonian biostratigraphy in Jiangsu, the Lower Yangtze Platform[END_REF],

and [START_REF] Li | Cishan Formation-Early Aikuanian strata in the Nanjing region[END_REF]. In the 1990s, Lu (1994a) From the Hubei and Hunan provinces, a considerable amount of literature on the palynofloral assemblages and biostratigraphy has been published (e.g. [START_REF] Hou | Some spore assemblages of the Devonian-Carboniferous transition from Xikuangshan District, central Hunan[END_REF][START_REF] Liu | Conchostracans and spores of Upper Devonian Huangjiadeng Formation in Hubei Province[END_REF][START_REF] Wang | The Devonian-Carboniferous boundary of benthonic facies in central Hunan[END_REF][START_REF] Yang | Spores[END_REF]Gao, 1990a;[START_REF] Fang | A New Advancement of the Devonian-Carboniferous boundary in Central Hunan Province, China[END_REF][START_REF] Wang | Miospore assemblages from the Shaodong and Mengkung'ao Formations at Xikuangshan, central Hunan with discussion on Devonian-Carboniferous boundary[END_REF][START_REF] Lu | Miospores from Shaodong Member at Jieling Section of Hunan, China and their geological age[END_REF]Lu, , 1997a;;[START_REF] Li | Devonian plants and stratum in Wuhan, Hubei Province, China[END_REF]. The pioneering work of the spore assemblages from the Devonian-Carboniferous Boundary (DCB) of the Xikuangshan district in the Hunan province was published by [START_REF] Hou | Some spore assemblages of the Devonian-Carboniferous transition from Xikuangshan District, central Hunan[END_REF]. Subsequently, [START_REF] Wang | Miospore assemblages from the Shaodong and Mengkung'ao Formations at Xikuangshan, central Hunan with discussion on Devonian-Carboniferous boundary[END_REF] Tournaisian). In addition, similar reports have been published from other regions, for instance Guangxi [START_REF] Yang | Palynological study of the Devonian-Carboniferous boundary in the vicinity of the International Auxiliary Stratotype Section, Guilin, China[END_REF], Sichuan [START_REF] Lu | Upper Devonian (Frasnian) sporopollen assemblage from the Damaidi area of Dukou, Sichuan Province[END_REF], and Guizhou (Gao, 1991a).

Western Yunnan

The miospore assemblages of western Yunnan were roughly distinguished from the uppermost Devonian and Lower Carboniferous sediments of Gengma County by [START_REF] Yang | Stratigraphic and phytogeographic palynology of late Paleozoic sediments in western Yunnan, China[END_REF]. In ascending order, they are the Retispora lepidophyta, Grandispora spiculifera, and Lycospora pusilla zones.

Tarim

The majority of the terrestrial palynofloras from the Late Devonian and earliest Carboniferous from Tarim were studied by Huaicheng Zhu and his colleagues. The reported strata encompass the Qizilafu (Famennian) and Bachu formations (Famennian) in the southern Tarim Basin (Fig. 3b, location 38) [START_REF] Gao | Discovery and significance of Retispora lepidophyta from Qizilafu group, Yecheng County, Xinjiang[END_REF][START_REF] Zhu | Discovery of Late Devonian spores from the Southwestern margin of Tarim basin and their significance[END_REF]Zhu, , 1999b;;[START_REF] Zhu | Discovery of Late Devonian spores of the Bachu formation from the South of Xinjiang, and their stratigraphical significance. The "Nine Five" anthology of important achievements in national geological science and technology[END_REF], the Bacan borehole 1 from Bachu County in the western Tarim Basin (Fig. 3b, location 42) [START_REF] Gao | Late Devonian of Sporopollen Bacan well 1 in West Tarim Basin and its stratigraphic significance[END_REF], the Donghetang Formation from the northern Tarim Basin (Fig. 3b, locations 22 and 39) (Zhu, 1999a[START_REF] Zhu | Upper Devonian spores from the North Tarim Basin, NW China[END_REF], and the Bachu Formation of the central Tarim Basin (Fig. 3b, location 41) (Zhu et al., 1998). Zhu and Zhao (1999)

Qinling

The terrestrial palynofloras from this region remain poorly known compared to other regions. In addition to [START_REF] Gao | Late Silurian and Devonian spores from west Qinling MTS., China. In: Late Silurian and Devonian stratigraphy and palaeontology from west Qinling MTS. Xi'an Institute of geology and mineral resources of ministry of geology and mineral resources[END_REF] study mentioned above, Gao (1990b) described the palynomorphs (including spore assemblages, a small number of acritarchs and scolecodonts) from the Wangjiadian Formation in Zhangxian, Gansu (Fig. 3b, location 32), with two spore assemblage zones established, in ascending order: Retispora lepidophyta-Knoxisporites literatus (LL; Famennian), and Retispora lepidophyta-Hymenozonotriletes explanatus (LE; Famennian).

Junggar

In addition to [START_REF] Xu | Devonian spores from an intra-oceanic volcanic arc, West Junggar (Xinjiang, China) and the palaeogeographical significance of the associated fossil plant beds[END_REF], [START_REF] Lu | Upper Devonian acritarchs and spores from the Hongguleleng Formation, Hefeng district in Xinjiang, China[END_REF] recovered diverse palynofloras containing the spores and acritarchs from the Upper Devonian Hongguleleng Formation, Hefeng District (Fig. 3b, location 12), Xinjiang.

Subsequently, [START_REF] Lu | On the miospore assemblages of the heishantou formation at aherbruckomha in Horboksar, Xinjiang, with additional reference to the transition stratum from Devonian to Carboniferous[END_REF] systematically described the diverse material from the Heishantou Formation and discussed the DCB of this area. The monograph published by [START_REF] Ouyang | The study of Carboniferous -Permian palynofloras in N. Xinjiang, NW China[END_REF] included numerous plates of the Carboniferous-Permian plant microfossils from northern Xinjiang, that are of great value for the understanding of plant microfossil evolution during this period.

2.4.6. Himalaya Gao (1983aGao ( , 1988b) ) investigated the Late Devonian spores and the DCB of Nyalam (Fig. 3b, location 40) in Tibet, and attributed the upper strata of the Boqu Group to the Late Devonian (Famennian). Moreover, a small number of acritarchs and scolecodonts have also been described.

Qilian-Qaidam Region

On the basis of the samples collected from the Qianheishan Formation (Tournaisian) of Jingyuan (Fig. 3b, location 46), Gansu, [START_REF] Gao | Lower Carboniferous spore assemblage from the Qianheishan formation of Jingyuan County, Kansu and its age[END_REF] described the spore assemblages including 33 genera and 69 species, that include 14 new species and 14 new combinations. In the 1990s, [START_REF] Gao | Carboniferous sporopollen from Qinghai and its stratigraphic significance[END_REF] reported the palynomorphs from the Chuanshan (early Tournaisian) and the Qianggou Formation (middle to late Tournaisian) and considered that they could be correlated with palynomorphs of western Europe, Russia, North America, and other regions. Qinling, Junggar, Qilian-Qaidam, Western Yunnan, Tarim, and Himalaya region (Fig. 3b). The Devonian palynological researchers in China have generally correlated their spore assemblages with each other and with those in Europe and North America;

hence in the present study, the original biostratigraphical data (Fig. 4) are used for the database. Some species names in the original publications were harmonized to remove nomenclatural errors that might impede accurate measures of spore species-level diversity. For example, spelling mistakes in the original literature have been corrected, such as Triletes langii, that is here attributed to Rhabdosporites langii (see [START_REF] Xu | Middle and early Late Devonian megaspores from eastern Yunnan[END_REF]. The final database contains 1677 species belonging to 190 genera from The total number of taxa of a given rank of a fossil group known from each of several successive intervals of geological time is commonly used as a measure of the relative taxonomic diversity of the group during the respective time intervals [START_REF] Raup | Taxonomic diversity during the Phanerozoic[END_REF][START_REF] Sepkoski | Stratigraphic biases in the analysis of taxonomic survivorship[END_REF]. On the basis of synthetic range data, taxa are regarded as present in a stratigraphical interval in one of four possible mutually exclusive, fundamental classes [START_REF] Foote | Origination and Extinction Components of Taxonomic Diversity: General Problems[END_REF][START_REF] Alroy | Fair sampling of taxonomic richness and unbiased estimation of origination and extinction rates[END_REF]: as crossovers ranging throughout the entire interval (sampled or not in it); ranging into and going extinct in that interval (bottom boundary crossers); originating within the interval and ranging beyond its upper boundary (top boundary crossers); and as single-interval, with a range confined to an interval, meaning that they originate and go extinct within the interval.

Then again, depending on the relative weights according to each class of range with regard to their occurrence in and around a stratigraphical interval, several taxonomic richness indices can be calculated (Fig. 6). 1) The sampled-in-bin diversity (Dsib) is the most straightforward index by providing the total count of taxa actually documented from a given stratigraphical interval, but it commonly underestimates diversity due to the incompleteness of the fossil record and sampling bias.

2) The range-through or total diversity (Drt-: rang-through diversity; Appendix D) is the most traditional approach by counting all actual and inferred occurrences of the considered stratigraphical bin.

3) The single-interval diversity (Dsgl) counts the taxa documented in a single bin. 4) The crossover diversity (Dover), in contrast to the single-interval diversity, counts taxa that are documented both before and after the considered stratigraphical interval and can be considered to roughly represent the diversity of long-ranging taxa. 5) The normalized diversity (Dnorm) is considered a good approximation of the mean standing diversity in a stratigraphical bin [START_REF] Cooper | Measures of diversity[END_REF] by summing the taxa ranging from the interval below to the interval above, plus half the number of taxa originating and/or becoming extinct within the interval, plus half of those that are confined to the interval itself [START_REF] Sepkoski | Stratigraphic biases in the analysis of taxonomic survivorship[END_REF]. 6) The estimated mean standing diversity (Demsd) is similar to Dnorm, except that this method excludes the count of single-interval taxa (see [START_REF] Cooper | Measures of diversity[END_REF]. 7) Finally, the boundary crosser diversity (Dbtr) is also calculated.

It is now well-known that the number of recovered taxa within samples highly depends on the number of collected individuals leading to the sampling bias. Unequal sample sizes can lead to an effect similar to unequal time intervals: the more sampled the interval, the higher the diversity (everything else being equal). In order to partly overcome the biases of sampling and binning and the pitfall of single-interval taxa, some diversity indices focus only on the boundary crossers (see [START_REF] Foote | Origination and Extinction Components of Taxonomic Diversity: General Problems[END_REF]. The boundary crosser diversity straightforward counts the number of common taxa between two successive stratigraphical intervals. Since several years, the reconstruction of palaeobiodiversity trajectories emphasized the need to use samplebased over range-based data. The former data enable using resampling techniques to correct the overwhelming sampling bias. The classical approach to tackle the sampling bias was to use rarefaction [START_REF] Hurlbert | The non concept of species diversity: a critique and alternativeparameters[END_REF] to subsample all of the samples and calculate their richness at the same number of individuals (i.e. same sample size).

The sample-based rarefaction analysis (Raup,1975) was considered to be one of the best methods which have been used by many palaeontologists (e.g. [START_REF] Miller | Calibrating the Ordovician Radiation of marine life: implications for Phanerozoic diversity trends[END_REF]Shen and Shi, 2002). This method can compare the fossils of sampling size of different intervals on the same scale. We used a series of species/genus rarefaction analyses to evaluate the actual effects of sampling intensities in the different intervals, and 120 genus occurrences from China (Fig. 7A) and South China databases (Fig. 7B).

Indices of origination and extinction represent, respectively, the number of species/genera originating and becoming extinct in a stratigraphical interval. The turnover in an interval is measured by the sum of origination and extinction values.

These indices of taxonomic change can be calculated as including or excluding singletons, while the presence of a mass of single-interval taxa is the main cause of the diversity deviation [START_REF] Chen | Methods for paleobiodiversity measurement and case studies of their applicability[END_REF]. In Fig. 8, the singletons are excluded.

The use of stages as the stratigraphical intervals in this analysis implies that they are inevitable of different durations, which may cause partial bias, i.e., longer bins may have a higher taxonomic richness than shorter bins simply, for instance, the duration of Famennian (13.3 Myr) is over four times that of Pragian (3.2 Myr) (Cohen et al., 2013, updated). To correct for a possible bias resulting from these unequal interval lengths, rates of origination, extinction, and turnover have also been computed. They are equal to the origination, extinction and turnover indices divided by the stage duration in Myr (from Cohen et al., 2013, updated).

Main diversity fluctuations detected in the Devonian plant microfossil record of China

The Devonian taxonomic diversity curves for the Chinese plant microfossils are shown in Fig. 6. We see a regular increase of taxonomic richness throughout the entire Devonian (Drt-, Dsib). However, this pattern is strongly influenced by the concomitant increase of single-interval taxa (Dsgl) and may also be biased by a time-dependent sampling effort (see time-ratios). Discarding these potential biases, the pattern is rather of a sudden strong increase of richness in the Pragian (not at the Silurian/Devonian boundary) (see Dbtr) followed by a plateau of richness, whereas the size-based rarefaction (Fig. 7) shows another pattern with an increasing trend until the Givetian, followed by a plateau.

Moreover, regarding origination/extinction values the trend of the origination index in both China and South China is quite similar to that of the turnover indices, with three peaks occurring in the Early Devonian, Givetian and Famennian (Fig. 8; Appendix E). Relatively higher values appear in the Emsian when using the raw taxonomic indices, but they disappear when conducting the rate of taxonomic change per Myr. Otherwise, the extinction indices have higher values in the Emsian and Famennian from both rates of taxonomic change per Myr and raw indices.

In terms of the comparison of the diversity of the individual terranes, in addition to the Junggar region (Fig. 9B), it is impossible for us to obtain more objective and realistic curves for the time being in other terranes such as Western Yunnan (Fig. 9A), Qinling (Fig. 9C), and Hinggan (Fig. 9D) region, due to lack of data.

The correlation of rarefaction estimated genus diversity and monographic (references per stage) richness in China gets the lowest value of such four methods (Dsib, Dnorm, Demsd, and rarefaction) and is not significant (Fig. 10; Appendix B).

Discussion

Devonian diversity pattern of observed palynofloras according to different measurement parameters

Land plant microfossils, that are much more abundant and widespread than land plant megafossils. They can supply reliable quantitative data to better understanding links between early land plant evolution and geological or palaeoenvironmental changes, even at the global level. Various indices, including Dsib, Drt-, Dnor, Demsd, Dbtr, and sample-based rarefaction analysis, have been used for discussing the diversity trajectories of Devonian plant microfossils (Fig. 6; Fig. 7). Interestingly, the correlation of Demsd (species level) and monographic (references per stage) richness is low and not significant (Fig. 10C), which means that the Demsd index may be more qualified for reducing the effect of sampling bias. [START_REF] Chen | Methods for paleobiodiversity measurement and case studies of their applicability[END_REF] analyzed the applicability of various diversity statistic methods, such as Drt-, Drt-/my, Dnor, and Demsd, and found out that the Demsd is not affected by the uneven duration of each time bin when the proportion of the singleton is moderate. Although Dbtr is still prone to the sampling bias, the Dbtr index is often preferred to Demsd and Dsib indices. Thus, when both Demsd and Dbtr are used at the same time, the conclusion may be more realistic to represent a general tendency of taxonomic diversity when sample-based data cannot be achieved.

The taxonomic raw data-based diversity pattern of plant microfossils through the Devonian in China is not only fairly similar to the plant megafossil and/or microfossil record at the global level (Fig. 11B; [START_REF] Knoll | Character Diversification and Patterns of Evolution in Early Vascular Plants[END_REF][START_REF] Cascales-Miñana | Apparent changes in the Ordovician-Mississippian plant diversity[END_REF], but also to the regional patterns of mega/macrofossils from Laurussia (Raymond and Metz, 1995, fig. 2), and South China (Fig. 11C,E; [START_REF] Wang | The evolution of Paleozoic vascular land plant diversity of South China[END_REF][START_REF] Xiong | Diversity Dynamics of Silurian-Early Carboniferous Land Plants in South China[END_REF]. Overall, the various diversity curves produced in the present study have a similar rising tendency (Fig. 6) on the basis of the range-based data, with an interruption by two major decreases that can be observed in the Eifelian and in the Frasnian. However, when these trajectories (especially the Dsib, Drt-) are compared with the adjusted results from sample-based rarefaction analysis, it becomes visible that they are quite different, especially during the Late Devonian. Results from rarefaction analysis suggest that a substantial portion of the increase for the Late Devonian may be a consequence of increased sample size of the fossil record. The discordance between raw diversity and more robust taxonomic diversity metrics suggests that sampling effects may strongly influence the perception of biodiversity trends. Genus diversity reached a peak in the later part of the Middle Devonian (Givetian), followed by a plateau persisting through the Late Devonian (Fig. 7). It is noteworthy that this result is in agreement with the classic studies of the apparent trend of plant megafossil diversity ( e.g. [START_REF] Knoll | Character Diversification and Patterns of Evolution in Early Vascular Plants[END_REF]. When we look at the diversity curves of the Junggar region (Fig. 9B), although these diversity patterns are very similar to the result of the rarefaction analysis, i.e., the apparent terrestrial palynofloral diversities progressively increased through the Early to Middle Devonian time interval, with a peak reached towards the latter part of the Middle Devonian (Givetian) followed by a plateau persisting through the Late Devonian, we should be careful because this can be caused by incomplete microfossil record.

Furthermore, the reported plateau of Late Devonian in the Chinese pattern of plant microfossil diversity also confirms previous observations concerning the absence of a

Frasnian-Famennian depletion of diversity like those occurred in marine realms in one of the recognized " Big Five" mass extinction (e.g. Bambach et al., 2004;[START_REF] Cascales-Miñana | Plants-the great survivors! The Geologists[END_REF][START_REF] Percival | Precisely dating the Frasnian-Famennian boundary: implications for the cause of the Late Devonian mass extinction[END_REF]. This trend is observed in both plant megaand micro fossil diversity patterns at global and regional scales (Fig. 11), which suggests a solid pattern of vegetation diversification towards the end-Devonian.

Diversity of Devonian plant microfossils and its possible relationship to marine oxygenation

The analysis of oxygen levels during the history of the Earth's have received much attention and is a subject of continuous debate among palaeontologists and modelling scientists (e.g. [START_REF] Berner | GEOCARBSULF: A combined model for Phanerozoic atmospheric O2 and CO2[END_REF][START_REF] Dahl | Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish[END_REF][START_REF] Sperling | Statistical analysis of iron geochemical data suggests limited late Proterozoic oxygenation[END_REF].

It is generally hypothesized that the evolution of land plants is intimately linked to the oxygenation of the oceans and the atmosphere but also to the decrease of carbon dioxide (e.g. [START_REF] Hir | The climate change caused by land-plant invasion[END_REF][START_REF] Lenton | Earliest land plants created modern levels of atmospheric oxygen[END_REF]. Most probably first nonvascular plants colonized the land somewhere during the Middle to Late Ordovician (~470-445 Ma), followed probably by the first vascular plants in latest Ordovician or the Silurian (~445-420 Ma), before becoming abundant and widespread during the Early Devonian (~420-390 Ma) [START_REF] Rubinstein | Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana)[END_REF][START_REF] Wellman | Palaeophytogeography of Ordovician-Silurian land plants[END_REF][START_REF] Edwards | Could land-based early photosynthesizing ecosystems have bioengineered the planet in mid-Palaeozoic times?[END_REF][START_REF] Gerrienne | Plant evolution and terrestrialization during Palaeozoic times-The phylogenetic context[END_REF]. By the end of the Middle Devonian, forests with trees exceeding 8 m in height had evolved in several independent clades [START_REF] Kenrick | A timeline forterrestrialization: consequences for the carbon cycle in the Palaeozoic[END_REF]). It appears therefore evident that significant changes in terms of weathering processes, as well as oxygen and carbon dioxide concentrations could have took place during the Devonian due to the colonization of land plants. This was already suggested two decades ago by [START_REF] Algeo | Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events[END_REF] and [START_REF] Algeo | Effects of the Middle to Late Devonian spread of vascular land plants on weathering regimes, marine biotas and global climate[END_REF].

More recently, additional papers have also mentioned global oxygenation events in the Devonian (e.g. [START_REF] Wallace | Oxygenation history of the Neoproterozoic to early Phanerozoic and the rise of land plants[END_REF]. The question if these models are consistent with the data must be raised.

The atmospheric oxygen levels are controlled in large part by the extent of organic carbon burial (e.g. [START_REF] Watson | Methanogenesis, fires and the regulation of atmospheric oxygen[END_REF][START_REF] Berner | The long-term carbon cycle, fossil fuels and atmospheric composition[END_REF][START_REF] Berner | GEOCARBSULF: A combined model for Phanerozoic atmospheric O2 and CO2[END_REF]. In existing models (see e.g. [START_REF] Bergman | COPSE: a new model of biogeochemical cycling over Phanerozoic time[END_REF][START_REF] Berner | A new model for atmospheric oxygen over Phanerozoic time[END_REF][START_REF] Berner | GEOCARBSULF: A combined model for Phanerozoic atmospheric O2 and CO2[END_REF], the evolution of trees starting ~385 Ma is assumed to have led to the burial of high C/P organic material, which is considered in these models to be much more significant than that from marine primary producers [START_REF] Kump | Terrestrial feedback in atmospheric oxygen regulation by fire and phosphorus[END_REF], potentially augmented by increased phosphorus weathering rates [START_REF] Lenton | Earliest land plants created modern levels of atmospheric oxygen[END_REF], although this is part of an ongoing debate. Some authors consider that it is reasonable to consider that the oxygen did not rise until the advent of forests starting at ~385 Ma (Givetian) [START_REF] Lenton | Earliest land plants created modern levels of atmospheric oxygen[END_REF].

The evidence from the isotopic composition and concentration of molybdenum (Mo) indicates a fundamental shift in the redox state of the deep ocean from widespread anoxia to widespread oxygenation sometime during the time interval from 435 to 392 Ma (between the Early Silurian and the Middle Devonian) [START_REF] Lenton | Earliest land plants created modern levels of atmospheric oxygen[END_REF]. This ocean oxygenation is also supported by a shift in iron speciation data sometime during a time interval from 435 to 387 [START_REF] Sperling | Statistical analysis of iron geochemical data suggests limited late Proterozoic oxygenation[END_REF]. [START_REF] Wallace | Oxygenation history of the Neoproterozoic to early Phanerozoic and the rise of land plants[END_REF] have recently tracked the sea-water oxygen levels of the Neoproterozoic and early Phanerozoic by using the relative abundance of cerium (Ceanom) in marine carbonates. Wallace et al.'s (2017) results indicate an apparent high pO2 increase through the Early Devonian to Middle Devonian, but that it was not until the Late Devonian that oxygenation levels are comparable to the modern world [START_REF] Wallace | Oxygenation history of the Neoproterozoic to early Phanerozoic and the rise of land plants[END_REF]. The increase of cerium anomaly closely coincides with the Middle Devonian (Givetian, [START_REF] Stein | Giant cladoxylopsid trees resolve the enigma of the Earth's earliest forest stumps at Gilboa[END_REF][START_REF] Wallace | Oxygenation history of the Neoproterozoic to early Phanerozoic and the rise of land plants[END_REF]. Interestingly, our results have shown that the plant microfossil diversity in China has been rising gradually from the Early Devonian to Middle Devonian (Givetian), followed by a plateau during the Givetian to Late Devonian (Fig. 7). So, the known geochemical pattern of Mo and Ceanom seem to be consistent with the land plant microfossil diversity trajectory, which could suggest that the Devonian evolution of a forested vegetation played a significant role in influencing the carbon cycle and atmospheric oxygen levels [START_REF] Edwards | Could land-based early photosynthesizing ecosystems have bioengineered the planet in mid-Palaeozoic times?[END_REF]. The present study therefore provides additional evidence that the rise of land plants appeared to have been essential for a possible oceanic oxygenation event during the mid-Devonian, instead of the Late Devonian as proposed by [START_REF] Wallace | Oxygenation history of the Neoproterozoic to early Phanerozoic and the rise of land plants[END_REF].

6.3.Devonian marine animal diversity, plant microfossil diversity and palaeoclimate

In the past decades, many works have discussed about Devonian climate changes (e.g. [START_REF] Streel | Late Frasnian-Famennian climates based on palynomorph analyses and the question of the Late Devonian glaciations[END_REF][START_REF] Van Geldern | Carbon, oxygen and strontium isotope records of Devonian brachiopod shell calcite[END_REF][START_REF] Joachimski | Devonian climate and reef evolution: Insights from oxygen isotopes in apatite[END_REF]. [START_REF] Joachimski | Devonian climate and reef evolution: Insights from oxygen isotopes in apatite[END_REF] reconstructed the sea surface palaeotemperature (SST) history of the Devonian. In their view, the earliest Devonian, the late Frasnian, and most of the Famennian are relatively warm periods, whereas the Middle Devonian represents a relatively cooler period [START_REF] Joachimski | Devonian climate and reef evolution: Insights from oxygen isotopes in apatite[END_REF]Hearing et al., 2018, fig. 3).

Although the Middle Devonian cooling remains debated, it was possibly linked to the plant evolution and also resulted in the long-term weathering of terrestrial ecosystems, and the reduction of atmospheric pCO2 (e.g. [START_REF] Algeo | Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events[END_REF]. [START_REF] Hir | The climate change caused by land-plant invasion[END_REF] considered that the drift of palaeocontinents, together with the impact of the terrestrialisation by land plants, can explain the climate changes. Le [START_REF] Hir | The climate change caused by land-plant invasion[END_REF] applied modeling data simulating a drop of pCO2 from 6300 to 2100 ppmv from the Early to the Late Devonian. The massive terrestrialisation by Devonian land plants surely must have had an impact on global pCO2 levels and climate changes, but what is its proportion to global tectonic changes or the evolving marine ecosystems? [START_REF] Klug | The Devonian nekton revolution[END_REF] displayed the diversification of various higher rank taxa of phytoplankton, zooplankton, demersal and pelagic nekton of the Devonian and Early Carboniferous. The three curves (Klug et al., 2010, fig. 4), which contain the integrated benthic genera, nektonic genera and marine genera with singletons, respectively, get strikingly high biodiversity values in the late Early to Middle Devonian. For example, as a well-preserved fossil group, bryozoans have important environmental significance, and their diversity displays a persistent rise from the Pragian to the early Givetian, before a significant drop from the late Givetian to the Famennian [START_REF] Horowitz | Devonian Bryozoan Diversity, Extinctions, and Originations[END_REF][START_REF] Ernst | Diversity dynamics and evolutionary patterns of Devonian Bryozoa[END_REF]Fig. 12C). A notable peak of marine animal diversity can be observed in South China during the late Early Devonian to Middle Devonian, representing highest levels that are recognized through the entire Devonian Period [START_REF] Rong | Dynamic patterns of latest Proterozoic-Palaeozoic-early Mesozoic marine biodiversity in South China[END_REF]; Fig. 12A). In addition, the diversity curves from other marine invertebrates, such as coral-stromatoporoid reefs [START_REF] Flügel | Patterns of Phanerozoic reef crises[END_REF][START_REF] Kiessling | Secular variations in the Phanerozoic reef ecosystem[END_REF][START_REF] Liao | Diversity of Devonian Rugose in South China[END_REF]; Fig. 12B), tentaculitoids (Fig. 12D), brachiopods [START_REF] Harper | Patterns of diversity, extinction and origination in the Ordovician-Devonian stropheodontacea[END_REF][START_REF] Chen | The diversity and evolvement characteristics of the brachiopods in South China[END_REF] and trilobites [START_REF] Richard | Treatise on Invertebrate Paleontology. Part O. Arthropoda 1. Trilobita, Revisited[END_REF] The diversity pattern of terrestrial palynofloras is notably different from that of contemporaneous marine animals, at a global level, especially in the Late Devonian.

The diversity trajectory of terrestrial palynofloras from China reaches a peak in the Givetian, followed by a plateau (with a slight decrease in the Frasnian and a slight rise in the Famennian) (see Dbtr in Fig. 6) extended to the Late Devonian. The taxonomic diversity in the Late Devonian was obviously higher than during the Early Devonian (Fig. 7), which is quite similar to the trends observed in Euramerica. On the basis of [START_REF] Richardson | Silurian and Devonia spore zones of the Old Red Sandstone continent and adjacent regions[END_REF] Euramerican data, [START_REF] Boulter | Patterns of plant extinction from some palaeobotanical evidence[END_REF][START_REF] Raymond | Laurussian Land-Plant Diversity During the Silurian and Devonian: Mass Extinction, Sampling Bias, or Both?[END_REF], fig. 3), and McGhee (1996) analyzed the Devonian diversity of miospore species, and indicated that the results clearly show a maximum during the Givetian-middle Frasnian and a rather dramatic drop from the late Frasnian to the middle Famennian in low latitude regions (see [START_REF] Streel | Late Frasnian-Famennian climates based on palynomorph analyses and the question of the Late Devonian glaciations[END_REF]. [START_REF] Streel | Late Frasnian-Famennian climates based on palynomorph analyses and the question of the Late Devonian glaciations[END_REF] suggested that a rather hot climate culminated during the latest Frasnian, when equatorial miospore assemblages reached their maximum distribution range, with the homogeneity of miospore assemblages presented from palaeo-tropical to palaeosubpolar regions during the Frasnian [START_REF] Streel | Givetian-Frasnian phytogeography ofEuramerica and western Gondwana based on miospore distribution[END_REF][START_REF] Streel | Late Frasnian-Famennian climates based on palynomorph analyses and the question of the Late Devonian glaciations[END_REF]. The low latitude warming during the middle to late Frasnian and early Famennian was later confirmed by the Devonian climate model of [START_REF] Joachimski | Devonian climate and reef evolution: Insights from oxygen isotopes in apatite[END_REF]. If correct, the relatively mild climate characteristic of the Givetian, with a less marked climatic gradient, would have played a significant role in the enhancement of plant microfossil diversity, while the rather hot climate during the latest Frasnian in the low latitudes, to some extent, may have limited the plant diversity increase. This can also be used to illustrate the relatively low levels of diversity during the Early Devonian. Similarly, the slight decrease of the temperature during the Famennian (375-359 Ma) may have contributed to the diversity increase [START_REF] Joachimski | Devonian climate and reef evolution: Insights from oxygen isotopes in apatite[END_REF]. It is noteworthy that the Devonian of China, in the eastern margin of the Palaeo-Tethys Ocean, displays a similar diversity pattern than that of Euramerica, located in similar latitudes at the western margin of the Palaeo-Tethys Ocean. However, these trends from China and Euramerica are significantly different from that of the Siberian landmass [START_REF] Gutak | Diversity and richness of the Devonian terrestrial plants in the Southeastern Mountainous Altay (Southern Siberia): Regional versus global patterns[END_REF]Fig. 11F). According to modern global plate tectonic reconstructions (e.g. [START_REF] Boucot | Phanerozoic Paleoclimate: AnAtlas of Lithologic Indicators of Climate[END_REF], Siberia was an isolated landmass located in mid-high latitudes during the Devonian. The different plant diversity dynamics exhibited between the Siberian landmass and China may have been affected by temperature variations controlled by latitude and/or oceanic currents (i.e. warm and cold currents).

It is likely that the diversities of marine animals and plant microfossils during the Devonian Period have strongly interacted with the contemporaneous climate changes, i.e., the comfortable climate of the late Early to Middle Devonian time interval, which is comparable to the present day, may have played a role in promoting the increases in biodiversities that characterized that time interval.

Plant microfossil diversity and sea-level changes

Although the relationships between sea-level changes and marine biodiversity have been abundantly discussed [START_REF] Algeo | Effects of the Middle to Late Devonian spread of vascular land plants on weathering regimes, marine biotas and global climate[END_REF][START_REF] Falkowski | The evolution of modern eukaryotic phytoplankton[END_REF][START_REF] Gutak | Diversity and richness of the Devonian terrestrial plants in the Southeastern Mountainous Altay (Southern Siberia): Regional versus global patterns[END_REF][START_REF] Katz | Evolutionary Trajectories and Biogeochemical Impacts of Marine Eukaryotic Phytoplankton[END_REF][START_REF] Li | Chinese Ordovician acritarch diversity curves[END_REF][START_REF] Ma | The Devonian System of China, with a discussion on sea-level change in South China[END_REF][START_REF] Ma | The Late Devonian Frasnian-Famennian Event in South China-Patterns and causes of extinctions, sea level changes, and isotope variations[END_REF]McGhee, 1992;[START_REF] Martin | Marine biodiversification in response to evolving phytoplankton stoichiometry[END_REF][START_REF] Miller | The Phanerozoic record of global sea-level change[END_REF][START_REF] Servais | The Ordovician Biodiversification: revolution in the oceanic trophic chain[END_REF][START_REF] Servais | The impact of the 'terrestrialisation process' in the late Palaeozoic: pCO2, pO2, and the 'phytoplankton blackout[END_REF][START_REF] Strother | A speculative review of factors controlling the evolution of phytoplankton during Paleozoic time[END_REF], no consistent conclusion has been reached so far, although it becomes clear that at the long term, i.e. the Phanerozoic scale, a tendency can be observed. [START_REF] Katz | Evolutionary Trajectories and Biogeochemical Impacts of Marine Eukaryotic Phytoplankton[END_REF] discussed the links between Mesozoic calcareous nannoplankton, dinoflagellates, diatoms, and sea-level changes, and indicate that the diversity of calcareous nannoplankton and dinoflagellates has good correspondence with the change of sea-level. [START_REF] Servais | The Ordovician Biodiversification: revolution in the oceanic trophic chain[END_REF] suggested that the Early Palaeozoic phytoplankton (acritarch) radiation paralleled a long-term rising of sea level between the early Cambrian and the Late Ordovician, while the highest phytoplankton diversity of the Palaeozoic was possibly the result of greatest continental dispersal and major orogenic and volcanic activity, which provided maximum ecospace and large amounts of nutrients. It thus appears that both major marine radiations in the Early Palaeozoic and in the Early Mesozoic are linked to the strong increase of sea-level that are accompanied by the diversification of the phytoplankton that most probably fueled the marine diversification [START_REF] Martin | Did the evolution of the phytoplankton fuel the diversification of the marine biosphere?[END_REF].

Increasing sea level floods more of the continental cratonic area, but also leads to an increase in the surface area of rock ultimately preserved at the outcrop [START_REF] Smith | Large-scale heterogeneity of the fossil record: implications for Phanerozoic diversity studies[END_REF]. [START_REF] Knoll | Phanerozoic land-plant diversity in north america[END_REF] discovered that a strong correlation existed between the outcrop area of nonmarine rocks deposited during a given geologic time interval and the observed vascular plant diversity for the same period. In fact, both the amount of sedimentary rock preserved and the nature of sedimentary environments have fluctuated significantly over time, and this has had a major effect on observed patterns of diversification and extinction [START_REF] Peters | Biodiversity in the Phanerozoic: a reinterpretation[END_REF][START_REF] Smith | Large-scale heterogeneity of the fossil record: implications for Phanerozoic diversity studies[END_REF][START_REF] Kenrick | A timeline forterrestrialization: consequences for the carbon cycle in the Palaeozoic[END_REF]. While sea-level is posited as a driver of terrestrial diversity, it is not clear how the volume of terrestrial clastic sediment could relate to sea-level [START_REF] Butler | Sea level, dinosaur diversity and sampling biases: investigating the 'commoncause' hypothesis in the terrestrial realm[END_REF][START_REF] Benton | Comparing the geological and fossil records: implications for biodiversity studies[END_REF].

It is now widely appreciated that the global sea level is generally considered to have risen throughout the Devonian (e.g. [START_REF] Johnson | Devonian eustatic fluctuations in Euramerica[END_REF]McGee, 1992;[START_REF] Miller | The Phanerozoic record of global sea-level change[END_REF][START_REF] Ma | The Devonian System of China, with a discussion on sea-level change in South China[END_REF][START_REF] Ma | The Late Devonian Frasnian-Famennian Event in South China-Patterns and causes of extinctions, sea level changes, and isotope variations[END_REF]. In South China, there are two large transgressiveregressive cycles recorded, i.e., in the Lochkovian to Eifelian, and in the late Eifelian to about the end of the Devonian Period [START_REF] Ma | The Devonian System of China, with a discussion on sea-level change in South China[END_REF]Fig. 12I).

Another important parameter to consider is sediment facies. Carbonate deposits are widely developed in South China throughout the Devonian Period, especially during the late Middle Devonian to the Late Devonian interval [START_REF] Zeng | Devonian lithofacies,paleogeography and mineralization in South China[END_REF].

However, although some can and do contain some beautifully (three dimensionally) preserved palynomorphs, carbonate sediments are prevailingly non-clastic, and most of them are relatively poor in palynomorphs. This is the main reason why most palynologists study fine-grained clastic sediments (i.e. siltstones) that contain high amounts of spores and pollen derived from land plants and not carbonate rocks [START_REF] Traverse | Paleopalynology[END_REF].The transgression events of the later Frasnian caused an extension of the carbonate platform belt in the low latitude regions, with a large dominance of carbonate versus clastic sediments in the geological successions. Consequently, only very few studies concerned palynomorphs in such strata deposited during the Frasnian and early Famennian in China. However, there have been a large number of publications at the global level, with more abundant records of Frasnian palynomorphs (Wicander and Playford, 1985 and references therein). The limited number of research may therefore explain at least partly the diversity decrease during the Frasnian in China. Subsequently, the progressive regression during the Devonian-Carboniferous transition increased the volume of terrestrial clastic sediments, with a much higher number of terrestrial palynofloral studies published concerning this time interval.

In the longer term, the sea-level rise increased the accumulation of terrigenous clastic sediments, which was crucial to the discovery of the Devonian terrestrial palynofloras. Over shorter timescales, however, the sea-level rise and the accumulation of carbonate platforms in low latitudes may have, in turn, caused an habitat and diversity loss of the terrestrial palynofloras. (modified from Alroy et al., 2008). G, genus-level diversity of plant microfossils from China from rarefaction estimated genus richness with error bars depict 95% confidence interval; H, estimated Devonian sea surface palaeotemperature record [START_REF] Joachimski | Devonian climate and reef evolution: Insights from oxygen isotopes in apatite[END_REF], the red band represents the modern equatorial sea surface temperature range [START_REF] Trotter | Did cooling oceans trigger Ordovician biodiversification? Evidence from conodont thermometry[END_REF]; I, sea-level curves of South China [START_REF] Ma | The Late Devonian Frasnian-Famennian Event in South China-Patterns and causes of extinctions, sea level changes, and isotope variations[END_REF] and Euramerica [START_REF] Johnson | Devonian eustatic fluctuations in Euramerica[END_REF].

Conclusion

This paper reviews the research progress on Devonian terrestrial palynofloras from China in the frame of Devonian plant micro-and megafossil diversity dynamics.

The research on many of the regions, except from South China, remains still very sparse. In addition, only a very small number of papers included discussions concerning palaeoclimate, palaeoecology, and palaeogeography and further work is needed to provide more comprehensive well-dated collections in some of the insufficiently studied regions.

Based on a newly compiled large-scale dateset (more than 1600 species and nearly 200 genera), a multimethodological statistical approach has been carried out. Resulted

Fig. 1

 1 Fig. 1 Photomicrographs of some Devonian spores. Magnification for (A)-(M) indicated by scale

Fig. 2

 2 Fig. 2 Publication rate of articles (between 1970 and 2017) used herein for the diversity analysis

Fig. 3

 3 Fig. 3 (a) Devonian palaeogeographical map (modified from Boucot et al., 2013) showing the

Fig. 4

 4 Fig. 4 Devonian stratigraphical framework of selected section areas from China. The

  acanthomammillatus-Dictyotriletes gorgoneus (AG) Biozone. More recently, Huang et al. (2016) investigated the spore assemblages from the Lower Devonian Guixi, Muerchang, Guanyinmiao, Guanshanpo formations, and from the Middle Devonian Jinboshi Formation, and established three spore assemblages in ascending order: Retusotriletes rotundus-Calamospora panacea (RP; Lochkovian), Synorisporites downtoniensis-Verrucosisporites scurrus (DS; Pragian-early Emsian), and Densosporites inaequus-Grandispora inculta (II; Eifelian-early Givetian).

  , who analyzed the spore assemblages of the Late Silurian to the Early Devonian from Shidian County, and who established the Apiculiretusispora spicula-), and Breconisporites breconensis-Cymbosporites dittonensis (BD) zones from the Niushiping (Pridolian), Xiangyangsi (Lochkovian), and Wangjiacun formations (?Pragian), respectively.

  described taxonomically the Early to Late Devonian palynomorphs of the Dangduogou section of Diebu County (Fig. 3b, location 3) and established six spore assemblage zones, in ascending order: Streelispora newportensis-Ambitisporites dilutus (ND), Reticulatisporites emsiensis-Clivosispora verrucata (EV), Rhabdosporites langii-Grandispora velata (LV), Densosporites devonicus, and Convolutispora crenata, Archaeozonotriletes spp.

  studied the miospores and megaspores and their stratigraphical significance of the Middle and Late Devonian time interval, with four spore assemblage zones established in ascending order: Calyptosporites velatus-Rhabdosporites langii (VL; Chuandong Formation; Eifelian), Archaeozonotriletes variabilis-Calyptosporites proteus (VP; Haikou Formation; Givetian), Geminospora lemurata-Cristatisporites triangulatus (LT; Haikou Formation; Givetian), and Archaeoperisaccus ovalis-Lagebicula bullosum (OB; Yidade Formation; Frasnian).

  3b, location 12) and eastern Yunnan (Fig.3b, location 2) and discussed their palaeogeographical and palaeoenvironmental significance. The discovery of Verrucisporites in both northern Xinjiang and eastern Yunnan indicates that a migration path may have been present for plants between South China and Laurasia.

  studied the spore assemblages from the Wutong Formation from Nanjing, Jiaingsu, and established four spore assemblage zones, in ascending order: Aneurospora asthenolabrata-Radiizonates longtanensis (AL; Famennian), Retusotriletes-Cymbosporites (RC; Famennian), Knoxisporites-Densosporites (KD; Tournaisian), and Leiotriletes crassus-Laevigatosporites vulgaris (CV; Tournaisian). It is important to note that[START_REF] Yang | The discovery of lower Carboniferous miospores assemblages from a borehole in the Binhai district, north Jiangsu[END_REF] paper was the first to research the miospores from a borehole in the Lower Carboniferous from northern Jiangsu (Fig.3b, location 47), and that this area may have been at the junction of the South China and North China plates.In Zhejiang,[START_REF] He | Spore assemblages from Devonian-Carboniferous transitional beds of Hsihu Formation, Fuyang, W. Zhejiang[END_REF] presented the spore floras from Devonian-Carboniferous transitional beds of the Xihu Formation in Fuyang, Zhejiang, from where two spore zones were built, in ascending order: Retispora lepidophyta-Apiculiretusispora hunanensis (LH; Famennian), and Dibolisporites distinctus-Cordylosporites papillatus (DP; Tournaisian). In addition,[START_REF] Yan | The microflora of the Tangjiawu and Xihu Formations in Zhejiang and their stratigraphical division and correlation[END_REF] introduced the microfloras from the Tangjiawu Formation (Wenlockian) and Xihu Formation (Famennian) in Zhejiang and their stratigraphical division and correlation. Recently, the spore assemblage zones of the Lower Yangtze Valley area (including Anhui, Jiangsu, and Zhejiang) were systematically investigated by Gao (2015). In ascending order, they can be divided into the following zones: Rugospora flexuous-Grandispora cornuta (FC; Famennian), Vallatisporites pusillites-Retispora lepidophyta (PL; Famennian), Retispora lepidophyta-Verrucosisporites nitidus (LN; Famennian), Vallatisporites verrucosus-Retusotriletes incohatus (VI; Tournaisian), Spelaeotriletes pretiosus-Cingulizonates bialatus (PB; Tournaisian), Schopfites claviger-Auroraspora macra (LN; Tournaisian), and Lycospora pusilla (PU; Visean).

  reported the progress of palynological studies of the Devonian-Carboniferous in the Tarim Basin, and established seven spore assemblage zones in ascending order: Apiculiretusispora hunanensis-Ancyrospora furcula (HF; Famennian), Cymbosporites spp.-Retusotriletes incohatus (SI; Tournaisian), Verrucosisporites nitidus-Dibolisporites distinctus (ND; Tournaisian), Spelaeotriletes balteatus-Rugospora polyptycha (BP; Tournaisian), Lycospora-Grumosisporites (LG; Visean), Cyclogranisporites pressoides-Florinites spp. (PS; Visean), and Schulzospora campyloptera-Schulzospora ocellata (CO; Visean-Namurian).

Fig. 5 .

 5 Fig. 5. Devonian stratigraphical scheme and stratigraphical ranges of palynological studies in

  China. It is worth pointing out that most of the records in the Devonian database from China are concentrated in the South China plate, comprising1285 species belonging to 175 genera. The studies from other regions, such as those from Western Yunnan and Hinggan, are still relatively sparse.We have measured the diversity changes over time using both range-based data, which simply record the synthetic presence (incidence) of each taxon through the successive ordered chronostratigraphical units (i.e. a range chart), and sample-based data, which, are an exhaustive record of all taxa within all samples/beds/collections of the studied time interval. Various methods therefore have been developed (for both these range-based and sample-based data) to overcome or compensate for these biases. Nowadays, the sample-based estimators are preferred to range-based estimators for palaeobiodiversity analyses, because they allow correcting (at least partly) the predominant and unavoidable sampling bias by means of resampling (rarefaction) methods. Data analysis is run at the species and genus ranks. Such analysis is computed at the chronostratigraphical rank of the Devonian stages(Cohen et al. 2013, updated) and was performed by using the free, popular, scientific environment R (R Core Team 2018) version 3.3.3 and with the package 'ePaleo' (Monnet C, unpublished, University of Lille; for applications using this package, see[START_REF] Nowak | Phytoplankton dynamics from the Cambrian Explosion to the onset of the Great Ordovician Biodiversification Event: A review of Cambrian acritarch diversity[END_REF][START_REF] Amberg | The nature of Ordovician limestone-marl alternations in the Oslo-Asker district (Norway): witnesses of primary glacio-eustasy or diagenetic rhythms?[END_REF][START_REF] Tetard | Biodiversity patterns of Silurian Radiolaria[END_REF]) version 0.7.37. Sizebased rarefaction was computed with Palaeontological Statistics (PAST) v.3.06[START_REF] Hammer | PAST: Paleontological Statistics Software Package for Education and Data Analysis[END_REF].

  and to verify the variation patterns of Devonian terrestrial palynofloral diversity dynamics of China and South China. The database of the plant microfossils contains 190 genera, 4568 occurrences in China, and 175 genera, 3363 occurrences in South China, respectively. The Devonian diversity trajectories were recast based on rarefaction estimates of genus richness for each time interval at a sample size of 230

Fig. 6

 6 Fig. 6 Taxonomic diversity curves of Devonian terrestrial palynofloras. A, species-level diversity in

Fig. 7

 7 Fig. 7 A-B: comparative rarefaction curves for the seven Devonian stages based on analysis of the

Fig. 8

 8 Fig. 8 Taxonomic origination, extinction and turnover rates of spore genus and species of China and

Fig. 9

 9 Fig. 9 Taxonomic diversity curves of Western Yunnan (A), Junggar (B), Qinling region (C), and

Fig. 10

 10 Fig. 10 Correlation (Rrho and Rtau) of taxonomic (Dsib, Dnor, Demsd, and rarefaction) and

Fig. 11

 11 Fig. 11 Comparative diagram showing relationships among the raw diversity of Devonian miospores and the megafossil pattern of land plants from China and other regions. A, plant microfossil data from all areas of China (Drt-); B, global plant microfossil data (modified from Cascales-Miñana, 2016); C, plant microfossil data from South China; D, global data from all land plants (modified from Cascales-Miñana, 2016); E, data of land-plants from South China (modified from[START_REF] Wang | The evolution of Paleozoic vascular land plant diversity of South China[END_REF]; F, data of land plants from southern Siberia (modified from[START_REF] Gutak | Diversity and richness of the Devonian terrestrial plants in the Southeastern Mountainous Altay (Southern Siberia): Regional versus global patterns[END_REF].

  Fig. 12E) highlight also relatively high diversity values over the Middle Devonian period. Alroy et al. (2008) used genus-level diversity measures during the Phanerozoic, based on sampling-standardized analysis of the Paleobiology Database. Placed in 48 temperal bins of a length averaging 11 Myr, global marine diversity indicates a steady increase from the early Cambrian to the Early Devonian, with a rapid decrease in the Middle Devonian before a rise in the Late Devonian.

Fig. 12

 12 Fig. 12 Comparative view of the main diversity fluctuations of important taxonomic groups and

  patterns have shown how the Devonian diversity patterns of plant microfossils from China are characterized by progressive increase in diversity through the Early and Middle Devonian, with a peak reached in the Givetian, followed by a plateau persisting through the Late Devonian. Interestingly, the genus/species level microfossil-based total diversity curve of land plants from China is quite similar to that of the global record. Robust taxonomic diversity metrics via sample-based rarefaction analysis have suggested that sampling effects may have strongly influenced our perception of biodiversity trends of China and that the Late Devonian taxonomic richness may have been greatly overestimated. Moreover, a new evidence seems to support that land plants appear to have been important contributors for a possible oceanic oxygenation event. Terrestrial and marine diversity trends can tentatively be compared, with increasing trends of diversity up to the Middle Devonian for both realms.

Acknowledgments

This work was financially supported by the Natural Science Foundation of China [grant numbers 41872034, 41290260] and China scholarship council (CSC). The authors are very grateful to Dr. Catherine Crônier (University of Lille, France), Huiping Peng and Junjun Song (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences) for offering some research materials.