氮沉降和刈割背景下草甸草原植物化学计量特征可塑性的多尺度耦联机制

The increases of atmospheric nitrogen deposition exert significant influence on biogeochemical cycling of biogenic elements in terrestrial ecosystems. The variation of stoichiometric ratios in plants is considered as a dominant controller for biogeochemical cycling of carbon and nutrients. Furthermore, it is theoretically predicted that the scaling of stoichiometric flexibility from plant organ to plant community is an important mechanism underlying the influences of nitrogen deposition on nutrient cycling. We still know little about the coupling of stoichiometric flexibility from plant organ to plant community, however, which restrict our ability to predict the effects of increasing nitrogen deposition on the biogeochemical cycling of biogenic elements. Moreover, there is a knowledge gap in the role of ecosystem management strategies in mediating the impacts of nitrogen deposition on stoichiometric characters. In the proposed project, we would like to examine the main and interactive effects of nitrogen deposition and mowing on the stoichiometric characteristics and flexibility at plant organ, individual, population, and community level in a temperate meadow steppe of northern China. The experiment will be carried out based on an experimental platform established since 2013. Findings from this project will improve our understanding about the interactive effects of nitrogen deposition and mowing on plant stoichiometry at diverse organization levels, and thus will provide direct and robust evidence for the influences of nitrogen deposition on plant-mediated biogeochemical cycles of biogenic elements. Furthermore, the results from this project will provide scientific supports for choosing appropriate adaptive management strategies under increasing nitrogen deposition scenario in temperate meadow steppe of northern China.

大气氮沉降对生态系统养分循环的影响不容忽视。植物化学计量特征的改变是调控生源要素生物地球化学循环的关键因素，而化学计量特征的可塑性从植物器官到群落水平上的推绎则是调控养分循环对氮沉降响应的重要机制。然而，我们对于不同组织水平上植物化学计量特征及其可塑性的耦联关系还知之甚少，这限制了我们预测氮沉降影响生态系统养分循环的能力。此外，植物化学计量特征及其可塑性对氮沉降的响应是否受生态系统管理措施的影响也是尚未解答的问题。为此，本项目拟依托已经建立的长期控制实验平台，运用生物地球化学、土壤化学、生态系统生态学方面的理论、技术和方法，从植物器官、个体、种群到群落等多个水平出发研究氮沉降和刈割背景下我国温带草甸草原植物碳氮磷化学计量特征及其可塑性。本项目旨在明确不同组织水平上生态化学计量特征可塑性的耦联关系，从生态化学计量的角度揭示氮沉降对生源要素生物地球化学循环的影响机制。

植物化学计量特征是调控生源要素生物地球化学循环的关键因素，而且这一特征会随着环境条件的改变而发生变化，即具有可塑性。化学计量特征的可塑性从植物器官到群落水平上的推绎是调控养分循环对氮沉降响应的重要机制。然而，我们对于从器官到群落水平上化学计量特征及其可塑性的耦联关系还知之甚少，这限制了我们预测氮沉降对生源要素生物地球化学循环影响的能力。此外，我们尚不清楚植物化学计量特征及其可塑性对氮沉降的响应是否受到生态系统管理措施的影响。本项目拟依托已经建立的长期控制实验平台，运用生物地球化学、土壤化学、生态系统生态学方面的理论、技术和方法，在2018到2021年间，从植物器官、个体、种群到群落水平研究氮素添加和刈割对我国北方草甸草原植物碳氮磷化学计量特征及其可塑性的影响。项目在氮素添加影响植物群落水平植物化学计量特征的种内和种间驱动力解析、刈割调控氮素添加对植物化学计量特征的影响以及常见植物化学计量可塑性的物种差异等方面取得重要研究进展，在Journal of Ecology、Biogeochemistry、Plant and Soil、Geoderma等领域主流期刊发表SCI论文14篇。研究结果对于理解氮素富集背景下植物介导的草甸草原生态系统氮磷元素的生物地球化学循环具有帮助作用。