Data from: Plant functional diversity modulates global environmental change effects on grassland productivity

1. Although much research has explored changes in ecosystem functions associated with global environmental changes, the mechanistic pathways behind the observed changes remain poorly understood. 2. Using an 11-year experiment that increased growing season precipitation and nitrogen deposition in a temperate steppe, we explored the relative importance of direct and indirect environmental change effects on plant primary productivity. 3. We show that increases in water and nitrogen availability influenced plant productivity via both direct and indirect pathways. While both treatments stimulated plant productivity, changes in plant productivity cannot be explained by observed changes in species or phylogenetic diversity. Instead, the indirect effects of water and nitrogen addition were through their positive effects on plant functional diversity. Importantly, while the increase in one component of functional diversity (community-level weighted mean of plant stature) resulted in increased productivity, the increase in another component of functional diversity (functional dispersion) resulted in decreased productivity. 4. Synthesis. Our study provides the first evidence for the opposite effects of community weighted means and functional dispersion of plant functional traits on grassland productivity, and highlights the importance of both traits of dominant species and trait distribution among species in modulating the effects of global changes on ecosystem functions.1. 尽管已有诸多研究探讨了全球环境变化驱动下的生态系统功能改变，但观测到此类变化背后的机制路径仍不甚明晰。 2. 本研究依托一项在温带草原（temperate steppe）开展的为期11年的野外控制实验，通过提升生长季降水量与氮沉降水平，解析了环境变化对植物初级生产力的直接与间接影响的相对重要性。 3. 研究结果表明，水分与氮素可利用性的提升可通过直接与间接两条路径影响植物生产力。尽管两项处理均促进了植物生产力，但植物生产力的变化无法通过观测到的物种多样性或系统发育多样性（phylogenetic diversity）的改变加以解释。与之相反，水分与氮素添加的间接效应是通过对植物功能多样性（plant functional diversity）的正向调控实现的。值得注意的是，功能多样性的其中一个组分——植物株高的群落加权均值（community-level weighted mean of plant stature）——的提升会提高草地生产力，而另一组分——功能离散度（functional dispersion）——的提升则会降低草地生产力。 4. 综合来看，本研究首次证实了植物功能性状的群落加权均值与功能离散度对草地生产力的相反调控效应，并强调了优势种性状与物种间性状分布格局在调节全球变化对生态系统功能影响过程中的双重重要性。