Data from: Nitrogen fertilization, not water addition, alters plant phylogenetic community structure in a semi-arid steppe

1. Anthropogenic environmental changes, such as nitrogen (N) enrichment and alteration in precipitation regimes, significantly influence ecosystems worldwide. However, we know little about whether and how these changes alter the phylogenetic properties of ecological communities. 2. Based on a seven-year field experiment in the temperate semi-arid steppe of Inner Mongolia, China, we investigated the influence of increased N and precipitation on plant phylogenetic structure and phylogenetic patterns of species colonization and extinction. 3. Our study demonstrated that N and water addition influenced different aspects of plant community structure. Water addition increased plant species richness by preventing species extinction and facilitating species colonization, without altering community phylogenetic structure. By contrast, N addition did not alter species richness, but promoted the colonization of species distantly related to the residents, changing community phylogenetic structure from being neutral to overdispersion. We also found evidence for abundance-based extinction where rarer species were at greater risk of extinction, and functional-based species extinction where shorter-statured plants and shallower-rooted plants were at greater risk of extinction. 4. Synthesis. Our study provides the first experimental evidence that plant phylogenetic community structure responds differently to different aspects of global changes. Importantly, the colonization of non-resident species, rather than the extinction of resident species, contributed predominantly to changes in plant community phylogenetic structure in response to N amendment. Our findings highlight the importance of considering species phylogenetic relationships for a more complete understanding of anthropogenic influences on ecological communities.1. 人为活动引发的环境变化（如氮（nitrogen, N）富集与降水格局改变）正显著影响全球范围内的各类生态系统。但目前我们对这类变化是否以及如何改变生态群落的系统发育属性（phylogenetic properties）仍知之甚少。 2. 本研究依托在中国内蒙古温带半干旱草原开展的7年野外控制实验，探究了氮素与降水添加对植物系统发育群落结构（phylogenetic community structure）以及物种定居与灭绝的系统发育模式的影响。 3. 本研究结果表明，氮素与水分添加对植物群落结构的不同维度产生影响。水分添加通过抑制物种灭绝、促进物种定居提升了植物物种丰富度，且未改变群落的系统发育结构。与之相对，氮素添加未改变物种丰富度，但促进了与本地群落亲缘关系较远的物种的定居，使群落系统发育结构从系统发育中性（phylogenetic neutral）转向系统发育过离散（phylogenetic overdispersion）。本研究还发现了基于多度的灭绝模式（abundance-based extinction）的证据：稀有物种面临更高的灭绝风险；以及基于功能性状的物种灭绝模式（functional-based species extinction）的证据：株高较矮、根系较浅的植物面临更高的灭绝风险。 4. 研究总结。本研究首次通过实验证实，植物系统发育群落结构对全球变化（global changes）的不同维度响应存在差异。尤为重要的是，在氮素添加的背景下，驱动植物群落系统发育结构变化的主要因素是非本地物种的定居，而非本地物种的灭绝。本研究结果凸显了考虑物种系统发育关系的重要性，这有助于更全面地理解人为活动对生态群落的影响。