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Keywords Devonian; Early vascular plants; South China; Guijiatun Formation; Dryland; Paleosols; Soil carbon Abstract The mid-Paleozoic colonization of land by plants induced profound changes in the Earth's surface environments. However, it remains poorly understood how the earliest vascular plants, arising during the Silurian and Devonian periods, adapted to and functioned in ancient drylands. Today, drylands occupy ~45% of the Earth's land surface and support diverse ecosystems forming the Earth's most extensive biome. By contrast, only sparse records of dryland systems have been documented from Silurian- and Devonian-aged deposits, and furthermore, in most cases, the evidence for recognizing major plant types is compromised by poor preservation potential of organic matter in such dry environments. Here, we recognize an Early Devonian dryland river system represented by the Guijiatun Formation, Qujing, Yunnan, South China, based on an integrative study combining paleopedology, geochemistry, and paleobotany. This formation contains diverse and abundant redbed calcareous paleosols, most being classified as Calcisols. Such paleosols are interpreted as developing within well-drained landscapes that experienced a semiarid climate with seasonal wet-dry cycles, and are geochemically characterized by the subsurface accumulation and reorganization of pedogenic carbonates. Extensive plant traces are preserved in most of the paleosols observed in the Guijiatun Formation and show K- or H-shaped branching structures that are morphometrically comparable to the belowground rhizomes of zosterophyllopsids and early lycopsids. These plant-bearing paleosols provide direct evidence for the development of primitive vegetation on drylands. The soil inorganic carbon (SIC) contents stored as Ca-Mg carbonates in the Guijiatun paleosols are estimated at 38 [plus or minus] 8 g C kg.sup.-1, comparable to the highest levels of present-day dryland ecosystems. We argue that dryland floras could have been a significant component of the Early Devonian landscapes, controlling the retention of both mobile elements (Ca and Mg) and fine-grained sediment on land, and mantling and protecting buried soil carbon against erosion. Author Affiliation: (a) The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, PR China (b) Center for Excellence in Life and Paleoenvironment, State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China (c) Beijing Museum of Natural History, Beijing 100050, PR China (d) Key Laboratory of Biogenic Traces & Sedimentary Minerals of Henan Province, Henan Polytechnic University, Jiaozuo 454003, PR China (e) School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, PR China (f) Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom (g) Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada * Corresponding author. Article History: Received 20 April 2022; Revised 13 December 2022; Accepted 14 December 2022 Byline: Jinzhuang Xue [pkuxue@pku.edu.cn] (a,*), Jiashu Wang (a), Pu Huang (b), Lu Liu (c), Tianzheng Huang (a), Lijun Zhang (d), Xianyan Wang (e), Bing Shen (a), Deming Wang (a), Jianbo Liu (a), Neil S. Davies (f), James F. Basinger (g)

Keywords Fossil record; Extinction; Vascular plants; Diversity; Permian; Triassic; North China Abstract A key question about the end-Permian mass extinction (EPME) is why it has been so difficult to determine its impact on land plants: some analyses show a very clear loss of diversity and yet others show little change. Perhaps the key issue is the scale at which the diversity data are analysed. Here we investigate plant diversity changes through the Permian to Middle Triassic in the North China Block (NCB) based on an updated dataset and diversity measured at different geographic-temporal scales. We define regional-scale diversity for the whole (palaeo)continent, including diverse depositional environments with plant fossils; landscape-scale diversity for a local area within the same depositional system, such as a fluvial or deltaic system; and bed-scale diversity for an individual bed formed in a relatively short time (e.g. less than 10,000 years). The floras from the Taiyuan, Shanxi, Lower Shihhotse, and Upper Shihhotse formations, and their lateral equivalents, seem to be relatively continuous and stable, dominated by wetland assemblages, with comparable diversities at bed, landscape and regional scales, and relatively stable extinction, origination, and turnover rates. The transition between the Upper Shihhotse and Sunjiagou formations (and lateral equivalents) saw the largest extinction of regional-scale generic and species diversity, with high extinction rates and low origination rates, but only slight changes in average bed-scale and landscape-scale diversities. After this, coal swamps disappeared, most widespread genera became extinct or shrank in distribution area, red beds became common, and surviving plants were walchian conifers, peltasperms and other advanced gymnosperms, indicating an overall drying trend in climate. A further extinction event happened at the transition between the Sunjiagou and Liujiagou formations (and lateral equivalents), with the highest species extinction and origination rates at regional scale. Almost all Permian plant species became extinct and were replaced by new taxa, while the bed-scale and landscape-scale diversities changed little. The Sunjiagou/Liujiagou transition event correlates with the marine EPME and the collapse of Gigantopteris-dominated communities in southwestern China, and probably represents the terrestrial equivalent of the EPME in the NCB. Author Affiliation: (a) School of Earth Sciences & Key Laboratory of Mineral Resources in Western China (Gansu Province), Lanzhou University, Lanzhou 730000, PR China (b) The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, PR China (c) Center for Excellence in Life and Paleoenvironment, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China (d) CNRS, University of Lille, UMR, F-59000 Lille, France (e) School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, United Kingdom * Corresponding author. Article History: Received 2 June 2021; Revised 15 October 2021; Accepted 24 October 2021 Byline: Conghui Xiong (a), Jiashu Wang (b), Pu Huang (c), Borja Cascales-Miñana (d), Christopher J. Cleal (e), Michael J. Benton (e), Jinzhuang Xue [pkuxue@pku.edu.cn] (b,*)