Data from: Environmental filtering by pH and soil nutrients drives community assembly in fungi at fine spatial scales

Whether niche processes, like environmental filtering, or neutral processes, like dispersal limitation, are the primary forces driving community assembly is a central question in ecology. Here, we use a natural experimental system of isolated tree “islands” to test whether environment or geography primarily structures fungal community composition at fine spatial scales. This system consists of isolated pairs of two distantly-related, congeneric pine trees established at varying distances from each other and the forest edge, allowing us to disentangle the effects of geographic distance versus host and edaphic environment on associated fungal communities. We identified fungal community composition with Illumina sequencing of ITS amplicons, measured all relevant environmental parameters for each tree - including tree age, size, and soil chemistry - and calculated geographic distances from each tree to all others and to the nearest forest edge. We applied generalized dissimilarity modeling to test whether total and ectomycorrhizal fungal (EMF) communities were primarily structured by geographic or environmental filtering. Our results provide strong evidence that, as in many other organisms, niche and neutral processes both contribute significantly to turnover in community composition in fungi, but environmental filtering plays the dominant role in structuring both free-living and symbiotic fungal communities at fine spatial scales. In our study system, we found pH and organic matter primarily drive environmental filtering in total soil fungal communities and that pH and cation exchange capacity – and, surprisingly, not host species - were the largest factors affecting EMF community composition. These findings support an emerging paradigm that pH may play a central role in the assembly of all soil mediated systems.

生态学界的核心议题之一，便是探明生态位过程（如环境过滤 (environmental filtering)）与中性过程（如扩散限制 (dispersal limitation)）何者是驱动群落构建的核心动力。本研究借助孤立树木“岛屿”这一天然实验系统，探究在精细空间尺度下，环境因素还是地理因素主导真菌群落组成的构建过程。该实验系统由两组亲缘关系较远的同属松树组成，每对树木彼此间以及与林缘的距离各不相同，借此我们得以厘清地理距离、宿主与土壤环境对关联真菌群落的影响差异。我们通过ITS扩增子 (ITS amplicons) 的Illumina测序技术鉴定真菌群落组成，测定每株树木的全部相关环境参数（包括树龄、树体大小与土壤化学性质），并计算每株树木与其他所有植株以及最近林缘的地理距离。我们采用广义相异性建模 (generalized dissimilarity modeling)，检验总真菌群落与外生菌根真菌 (ectomycorrhizal fungal, EMF) 群落的构建主要受地理因素还是环境过滤主导。本研究结果提供了强有力的证据：与诸多其他生物类群一致，真菌群落组成的周转同时受到生态位过程与中性过程的显著影响，但在精细空间尺度下，环境过滤仍是主导自由生活与共生真菌群落构建的核心因素。在本研究系统中，我们发现土壤pH与有机质是驱动总土壤真菌群落环境过滤的主要因素；而影响外生菌根真菌群落组成的最关键因素为pH与阳离子交换量——令人意外的是，并非宿主物种。上述发现支持了一项新兴研究范式：pH或许在所有土壤介导的生态系统构建过程中均发挥核心作用。