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. 人为环境变化（如氮（N）富集与降水格局改变）正显著影响全球各地的生态系统。然而，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特征（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年野外定位实验，探究了氮素添加与降水添加对植物系统发育群落结构（phylogenetic structure）以及物种定居与灭绝的系统发育格局（phylogenetic patterns）的影响。
3. 研究结果表明，氮素添加与降水添加对植物群落结构的影响维度存在差异。降水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，且未改变群落系统发育结构；与之相反，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中性模式转变为系统发育过度分散（phylogenetic overdispersion）模式。本研究还发现了两类物种灭绝效应：一是基于丰度的灭绝效应，即稀有物种面临更高的灭绝风险；二是基于功能性状的灭绝效应，即株高较矮、根系较浅的植物灭绝风险更高。
4. 综合分析：本研究首次通过控制实验证实，植物系统发育群落结构对全球变化的不同维度呈现出差异化响应。尤为重要的是，在氮素添加的背景下，非本地物种的定居（而非本地物种的灭绝）是驱动植物群落系统发育结构变化的主导因素。本研究结果凸显了考量物种系统发育关系的重要性，可为更全面地理解人为活动对生态群落的影响提供科学支撑。