氮沉降是当前对地表生物多样性影响最深刻的全球变化之一，氮沉降对植物-昆虫关系的影响是值得探讨的问题。氮沉降对植物群落的影响虽已被深刻理解，但对植食性昆虫的间接作用还关注较少，尤其缺少关于退化草地的研究。退化草地受氮的限制更强，氮沉降影响下，植物群落的任何变化都可能调控植食性昆虫的动态，后者又对前者形成反馈调节。识别这些因素的相对作用，以及氮沉降对植物-昆虫间的相互关系的影响机制十分关键。我们从2011年开始在内蒙古温带退化草地开展了长期实验，检验氮沉降对植物和土壤动物的影响，为本研究奠定了基础，也向我们提出新的挑战。在本项目中，我们将补充昆虫排除实验，分别检验氮沉降对植物生物量、化学物质组成，群落结构和多样性的直接影响，以及植食性昆虫对植物群落的反馈调节。我们还将通过结构方程模型来分析氮沉降对植食性昆虫产生间接影响的关键因素。本项目的实施将有助于更好的预测长期氮沉降对退化草地产生的后果。

Anthropogenic increases in nitrogen (N) deposition from atmosphere onto land is one of the most important factors currently driving global-scale biodiversity change. Plant-insect interaction has been one of hotspots. The direct effects of long-term nitrogen deposition on plant community (biomass or biodiversity) have received considerable attention, while less attention to the indirect effects on insect herbivores. Few studies have been conducted in degraded ecosystems, where organisms and ecological processes are limited by nitrogen deeply. Impacts on insect herbivores can be caused by changes in the plant quality, plant tissue chemistry, and/or species composition with nitrogen deposition. Vice versa, the changes in insect herbivores caused by nitrogen will potentially affect plant community by up-down control. Understanding the relative strength of these effects driving the change of insect herbivores is key to predict the true consequences of long-term nitrogen deposition. We propose to conduct a long-term nitrogen deposition experiment based on previous study since 2011 in a degraded grassland in Inner Mongolia to investigate the different effects of plant community on insect herbivores. We will conduct the herbivore exclusion experiment to test the feedback of herbivores on plant community and the direct influence fo nitrogen on plant commnity. We will also identify the key regulations of plant on herbivores by Structural Equation Modeling(SEM). The project will provide an insight can be used to assess the long-term consequence of N deposition on degraded temperate grasslands.