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 five 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，并加剧病原物的爆发与传播。尽管施肥对植物抗病性的直接效应已得到一定研究关注，但施肥通过改变群落结构所产生的间接效应对真菌病害侵染严重程度的影响，仍未得到充分探究。本研究在沿氮素施肥梯度设置的青藏高原高寒草甸自然植被群落中开展了为期五年的控制实验，以对比施肥的直接与间接效应对群落水平叶部真菌侵染的相对重要性。研究发现，对病原物易感程度较低的物种在施肥后更易被移除，由此使得群落水平的病害易感能力（进而群落病原负荷）随施肥强度的升高而增加。施氮量（直接效应）与群落病害易感能力（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。本实验为高度专一的病原-宿主系统中施肥后的自然群落的稀释效应（Dilution Effect）提供了机制性解释，由此为理解人类改造生态系统对传染病动态的影响提供了新的研究视角。