刈割能够缓解历史氮沉降对草地群落养分利用效率的负面影响

氮沉降的增加对草地生态系统结构和功能造成了诸多负面影响,包括改变植物群落结构和降低植物养分利用效率。许多国家的减排政策有效地减少了氮排放、降低了氮沉降速率,但历史氮沉降对生态系统的影响可能具有遗留效应。草地植物群落的养分利用效率在氮沉降减少或者停止后作出何种响应,还有待于研究。作为草地重要的管理方式之一,刈割将如何调控历史氮沉降对植物养分利用效率的影响仍然属于知识空白。本研究探讨了氮素添加停止以后连续3年内功能群水平和群落水平上植物的氮、磷利用效率对历史氮素添加和刈割处理的响应。研究结果表明,历史氮素添加显著降低了植物功能群水平的氮利用效率,但未改变其磷利用效率;在群落水平上,历史氮素添加显著降低了植物的氮磷利用效率。刈割能够缓解历史氮素添加对植物群落氮磷利用效率的降低作用,该作用主要是抑制具有较低养分利用效率的根茎型高禾草的生长而促进具有较高养分利用效率的丛生型高禾草的生长。研究结果揭示了植物群落结构在驱动植物群落养分利用效率变化中的重要作用。本研究认为适当的草地管理方式有助于氮沉降过后草地植物养分利用效率的恢复。

Linking changes of forage production and digestibility with grassland community assembly under nitrogen enrichment

Background:Forage production is the fundamental ecosystem service of grasslands.Although forage consumption occurs at community level,most studies focused on species-level changes of forage quality.The quantitative and qualitative changes of forage production are driven by species-specific trait,intra-specific plasticity,and species turnover.We examined the changes in forage production and digestibility after 5-year factorial treatments of nitrogen(N)addition and mowing in a temperate steppe and linked such changes to community assembly under the Price equation framework.Results:Nitrogen addition significantly reduced species richness,increased forage production,but did not change forage digestibility(indicated by the total Ca+Mg concentrations).Mowing did not affect forage production and digestibility.The positive effects of N addition on forage production were driven by the enhancement of abundance of the remaining species following N enrichment,rather than by species loss or species gain.The species identity effects could offset the effects of species richness loss or gain on forage production and digestibility.Conclusions:Our results highlight the importance of a community perspective in addressing the quantitative and qualitative changes of forage production under global change pressure of N enrichment.Species identity is important in determining the contribution of different processes of community assembly to ecosystem services.

Mowing weakens the positive effects of nitrogen deposition on fundamental ecosystem service of grassland

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.