Forage yield is the fundamental ecosystem service of grasslands. While the quantitative responses of forage yield to nitrogen (N) enrichment are well known, its qualitative responses remain unclear. Even less known is the relative contribution of changes in community composition to the quality of the yield at the community level. We examined the quantitative and qualitative responses of forage yield at both plant functional group and community levels with factorial treatments of N addition and mowing in a temperate steppe. Nitrogen addition significantly enhanced the community-level yield by favoring the growth of rhizomatous grass. Mowing tended to mediate the impacts of N addition on the yield. Nitrogen addition increased the concentrations of crude protein and crude fat in forage at the community level. Neither the main effects of mowing nor its interactive effects with N addition affected forage quality. The N-induced shifts in plant species composition significantly contributed to the effects of N addition on forage quality at the community level. Our results suggest that mowing wound weaken the positive effects of N deposition on the quantity but not the quality of forage yield. Changes in plant community composition are important in driving the qualitative responses of yield to N deposition.

中文翻译：

---

割草减弱了氮沉降对草地基本生态系统服务的积极影响

牧草产量是草原的基本生态系统服务。虽然众所周知，牧草产量对氮（N）富集的定量响应，但其定性响应仍不清楚。社区组成的变化对社区一级产量质量的相对贡献甚至鲜为人知。我们通过在温带草原中对氮的添加和修剪进行因子处理，研究了植物功能组和社区水平上草料产量的定量和定性响应。氮肥有利于根茎草的生长，显着提高了社区一级的产量。割草趋于介导添加氮对产量的影响。氮的添加增加了社区一级草料中粗蛋白和粗脂肪的浓度。割草的主要作用及其与氮的交互作用均不影响草料质量。N引起的植物物种组成的变化极大地促进了氮的添加对社区一级草料质量的影响。我们的研究结果表明，割草伤口会削弱氮沉降对草料产量的积极影响，但不会减弱其质量。植物群落组成的变化对于推动产量对氮沉降的定性响应至关重要。