Plant pathogens are often hypothesized to promote species coexistence by generating conspecific negative density dependence (CNDD). However, the relative importance of fungal versus oomycete pathogens in maintaining plant species coexistence and community composition remains unresolved, despite their recognized effects on plant performance. Here, we use fungicide application to investigate how fungal versus oomycete pathogens affect plant species coexistence in an alpine meadow. We found that the severity of foliar fungal disease was density-dependent at both intra- and interspecific levels. Fungal pathogen-exclusion treatment successfully decreased the severity of foliar fungal diseases, with no detectable effects on root colonization by arbuscular mycorrhizal fungi or on soil chemical properties. Fungal pathogens were important factors shaping CNDD across 25 coexisting plant species. Exclusion of fungal pathogens significantly reduced plant species richness and Shannon's evenness. Treatments that excluded fungal pathogens also led to significant shifts in plant community composition toward more Poaceae and Cyperaceae. These results indicate that fungal pathogens, especially those affecting aboveground plant parts, may play a larger role in maintaining species coexistence and shaping community composition than has been previously recognized.

中文翻译：

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真菌病原体比卵菌病原体更能通过同种负密度依赖性稳定共存

通常假设植物病原体通过产生同种负密度依赖性 (CNDD) 来促进物种共存。然而，真菌与卵菌病原体在维持植物物种共存和群落组成方面的相对重要性仍未得到解决，尽管它们对植物性能有公认的影响。在这里，我们使用杀菌剂应用来研究真菌与卵菌病原体如何影响高寒草甸中植物物种的共存。我们发现叶面真菌病的严重程度在种内和种间水平上都依赖于密度。真菌病原体排除处理成功地降低了叶面真菌病害的严重程度，对丛枝菌根真菌的根系定殖或土壤化学性质没有可检测到的影响。真菌病原体是影响 25 种共存植物物种 CNDD 的重要因素。排除真菌病原体会显着降低植物物种丰富度和香农均匀度。排除真菌病原体的处理也导致植物群落组成向更多的禾本科和莎草科显着转变。这些结果表明，真菌病原体，尤其是那些影响植物地上部分的病原体，在维持物种共存和塑造群落组成方面可能比以前认识到的发挥更大的作用。