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，在于判断驱动群落构建的核心动力究竟是以环境过滤为代表的生态位过程，还是以扩散限制为代表的中性过程。本研究依托孤立树木‘岛屿’这一天然实验系统，在精细空间尺度下探究环境与地理因素对真菌群落组成的调控作用。该实验系统包含多组由两种亲缘关系较远的同属松树组成的孤立配对样本，每对树木的间距以及单棵树木与林缘的距离均存在差异，借此我们可以分离地理距离、宿主属性与土壤环境对关联真菌群落的影响效应。研究人员通过对ITS扩增子进行Illumina测序以鉴定真菌群落组成，测定了每棵树木的全部相关环境参数——包括树龄、树体尺寸与土壤化学性质——并计算了每棵树木与其他个体及最近林缘的地理距离。我们采用广义相异模型（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调控。研究结果提供了强有力的证据：与多数其他生物类群一致，生态位与中性过程均对真菌群落组成的周转具有显著贡献，但在精细空间尺度下，环境过滤是调控自由生活与共生真菌群落构建的主导因素。在本研究系统中，我们发现土壤pH与有机质是调控总土壤真菌群落环境过滤的核心因子；而影响外生菌根真菌群落组成的最主要因素为pH与阳离子交换容量，且出乎意料的是，宿主物种并未发挥显著作用。上述发现支持了一个新兴研究范式：pH可能在所有土壤介导的生态系统群落构建过程中扮演核心角色。