Data from: Species decline under nitrogen fertilization increases community-level competence of fungal diseases

The artificial fertilization of soils can alter the structure of natural plant communities and exacerbate pathogen emergence and transmission. Although the direct effects of fertilization on disease resistance in plants have received some research attention, its indirect effects of altered community structure on the severity of fungal disease infection remain largely uninvestigated. We designed manipulation experiments in natural assemblages of Tibetan alpine meadow vegetation along a nitrogen-fertilization gradient over 5 years to compare the relative importance of direct and indirect effects of fertilization on foliar fungal infections at the community level. We found that species with lower proneness to pathogens were more likely to be extirpated following fertilization, such that community-level competence of disease, and thus community pathogen load, increased with the intensity of fertilization. The amount of nitrogen added (direct effect) and community disease competence (indirect effect) provided the most parsimonious combination of parameters explaining the variation in disease severity. Our experiment provides a mechanistic explanation for the dilution effect in fertilized, natural assemblages in a highly specific pathogen–host system, and thus insights into the consequences of human ecosystem modifications on the dynamics of infectious diseases.土壤人工施肥可改变自然植物群落结构，并加剧病原物的出现与传播。尽管施肥对植物抗病性的直接效应已受到一定研究关注，但其通过改变群落结构进而影响真菌病害侵染严重程度的间接效应，在很大程度上仍未得到探究。我们针对沿氮施肥梯度分布的青藏高原高寒草甸自然植被群落开展了为期5年的操控实验，以对比施肥对群落层面叶面真菌侵染的直接与间接效应的相对重要性。研究发现，对病原物易感程度较低的物种在施肥后更易被群落排除，进而导致群落病害传播能力（亦即群落病原负荷）随施肥强度的增加而升高。施氮量（直接效应）与群落病害传播能力（间接效应）构成了解释病害严重程度变异的最简约参数组合。本研究为高度特异的病原-宿主系统中施肥后的自然群落稀释效应提供了机制性解释，同时也为理解人类活动改造生态系统对传染病动态的影响提供了新的认知视角。