RESEARCH ARTICLE Driving factors of community-level plant functional traits and species distributions in the desert-wetland ecosystem of the Shule River Basin, China Guanguang Chen 1 | Dongxia Yue 1 | Yanyan Zhou 1 | Dong Wang 1 | Hai Wang 2 | Cang Hui 3 | Jianjun Guo 4 1 College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, PR China 2 Dunhuang Xihu National Nature Reserve Administration, Jiuquan, PR China 3 Centre for Invasion Biology, Department of Mathematical Sciences, Stellenbosch University, African Institute for Mathematical Sciences, Matieland, South Africa 4 Key Laboratory of Desert and Desertification, Northwest Institute Eco-environment and Resource, Chinese Academy of Sciences, Lanzhou, PR China Correspondence Dongxia Yue, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, PR China. Email: dxyue@lzu.edu.cn Funding information National Key Research and Development Plan of China, Grant/Award Number: 2017YFC1501005; National Nature Science Foundation of China, Grant/Award Numbers: 41671516, 41701623; National Research Foundation, Grant/Award Number: 89967 Abstract Groundwater, as the limiting resource in arid ecosystems, can have profound effects on the functional structure and distribution of plant communities. However, studies are too few to unveil the impacts of groundwater depth on plant functional traits in such communities. We collected data on vegetation, topography and soil properties from 180 quadrats (60 trees/shrubs and 120 herbaceous) in the desert-wetland eco- system of Shule River Basin in Northwest China. We measured 10 key community- level functional traits, together with the resource topography (i.e., groundwater depth) and seven soil properties. We found that the increase of groundwater depth significantly reduced community-level specific leaf area and maximum leaf photosyn- thesis rate, while boosted leaf dry mass content and leaf thickness. However, the leaf phosphorus content remained relatively stable. By contrast, with the increase of groundwater depth, soil carbon, soil nitrogen, soil phosphorus and total dissolved salts first increased but then declined, while soil pH and soil bulk density exhibited the opposite trend. The soil moisture content decreased drastically with the decline of groundwater. The change in groundwater depth, thus, was found the main driver of species distribution in the arid zone, contributing 21.16%, followed by soil K + (9.94%) and soil total nitrogen content (4.9%), as well as a strong interaction of the three (41.7%). Changes in groundwater depth can thus alter the structure and nutri- ent enrichment of the soil, which in turn affects the distribution of vegetation through water–soil–plant interactions. KEYWORDS driving factors, groundwater depth, plant functional traits, soil properties, species distribution 1 | INTRODUCTION Plant communities in arid ecosystems are under pressure from limited water resources. Of particular interest, desert-wetland is a type of vegetation uniquely adapted to extreme arid climates. It is mainly distributed in low-lying and dissolved-salt gathering areas in the tail- end-lake of the inland river. Worldwide, changes in wetland function and species composition in such arid ecosystems, due to drought and water shortages, have become a serious challenge to the conservation and restoration (Charles & Dukes, 2009; Holmstrup et al., 2012). Most arid and semiarid species depend on the capillary fringe above the groundwater for survival and growth; consequently, the decline of Guanguang Chen and Dongxia Yue contributed equally to this work. Received: 22 July 2019 Revised: 24 March 2020 Accepted: 12 April 2020 DOI: 10.1002/ldr.3624 Land Degrad Dev. 2020;1–15. wileyonlinelibrary.com/journal/ldr © 2020 John Wiley & Sons, Ltd. 1