群落内物种如何共存是群落生态学研究中最具争议的核心问题之一。根据当代物种共存理论框架，维持物种共存的机制可以分为稳定化和均等化机制。尽管地上病原真菌在自然界中大量存在，但是目前尚不清楚地上病原真菌如何通过稳定化和均等化机制从而影响物种共存。本研究拟采用地上杀菌处理（通过喷洒杀菌剂）降低地上病原真菌多度，通过邻体去除处理形成无邻居竞争植株，从而探究青藏高原高寒草甸地上病原真菌如何影响同种负密度制约（稳定化机制）和无竞争情景下的植物生长（表征适合度）。进而整合植物相对多度、功能性状和系统发育数据，检验：（1）高寒草甸的植物物种是否普遍受到同种负密度制约的限制（稳定化机制）；（2）生长能力较强的物种是否携带更多的叶真菌病害，且其生物量在杀菌处理后增长更多（均等化机制）。总之，本项目拟通过野外实验，检验地上病原真菌对植物物种共存的影响，并将地上病原真菌纳入到当代物种共存理论框架中。

Understanding how species coexist are core questions in community ecology that have long intrigued ecologists. Under the contemporary coexistence theory, the mechanisms that promote species coexistence are categorized into stabilizing and equalizing mechanisms. However, we know little about how aboveground fungal pathogens will affect stabilizing and equalizing mechanisms, despite being abundant and important. In this study, we will take the alpine meadow in the eastern part of Qinghai-Tibetan Plateau as model system. By using fungicides to decrease the abundance of aboveground pathogens, and neighbor removal to make plant individuals without neighbor competition, we will test how aboveground fungal pathogens affect the conspecific negative density dependence (i.e., stabilizing mechanism) and the plant growth ability without neighbor competition (estimating fitness). By combing the data of plant relative abundance, functional traits, and phylogeny, we will test: (1) whether plant species experience conspecific negative density dependence (stabilizing mechanism); and (2) whether plant species with greater growth ability harbor more pathogens thus benefit more from aboveground fungicide application treatment (equalizing mechanism). Overall, this study will combine the methods of field experiment and model fitting, trying to include aboveground fungal pathogens into the contemporary coexistence theory.