Effects of factorial nitrogen, phosphorus, and potassium with micronutrient addition and Host Community on Fungal Endophyte Diversity at Cedar Creek Ecosystem Reserve, Minnesota, USA, 2014

The microbes contained within free-living organisms can alter host growth, reproduction, and interactions with the environment. In turn, processes occurring at larger scales determine the local biotic and abiotic environment of each host that may affect the diversity and composition of the microbiome community. Here, we examine variation in the diversity and composition of the foliar fungal microbiome in the grass host, Andropogon gerardii, across a factorial nitrogen, phosphorus, and potassium addition experiment in Minnesota, USA. We found limited evidence of direct effects of nutrients on endophyte diversity. Instead, the effects of nutrients on endophyte diversity appeared to be mediated by accumulation of plant litter and plant diversity loss. Specifically, nitrogen addition is associated with a 40% decrease in plant diversity and an 11% decrease in endophyte richness. Although nitrogen, phosphorus, and potassium addition increased aboveground live biomass and decreased relative Andropogon cover, endophyte diversity did not covary with live plant biomass or Andropogon cover. Our results suggest that fungal endophyte diversity within this focal host is determined in part by the diversity of the surrounding plant community and its potential impact on immigrant propagules and dispersal dynamics. Our results suggest that elemental nutrients reduce endophyte diversity indirectly via impacts on the local plant community, not direct response to nutrient addition.

生存于自由生活宿主生物体内的微生物，可调控宿主的生长、繁殖过程，以及宿主与环境的互作关系。反之，更大尺度下的生态过程会决定单个宿主所处的局域生物与非生物环境，进而可能影响微生物组群落的多样性与组成结构。本研究依托美国明尼苏达州开展的氮、磷、钾全因子添加控制实验，探究了禾本科宿主大须芒草（Andropogon gerardii）的叶际真菌微生物组（foliar fungal microbiome）的多样性与组成变异情况。我们发现，养分对内生真菌（endophyte）多样性的直接调控证据十分有限；与之相反，养分对内生真菌多样性的影响似乎是通过植物枯落物积累与植物多样性丧失介导的。具体而言，氮素添加会导致植物多样性下降40%，同时伴随内生真菌丰富度降低11%。尽管氮、磷、钾添加提升了地上活体生物量，并降低了大须芒草的相对盖度，但内生真菌多样性并未与活体植物生物量或大须芒草盖度发生共变。本研究结果表明，该目标宿主体内的真菌内生菌多样性，在一定程度上由周围植物群落的多样性及其对迁入繁殖体与扩散动态的潜在影响所决定。综上，大量元素养分并非通过直接响应养分添加来影响内生真菌多样性，而是通过改变局域植物群落，间接降低了内生真菌的多样性。