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，即明确生态位过程（如环境过滤）与中性过程（如扩散限制）何者为驱动群落组装的核心动力。本研究依托孤立树木“岛屿”的天然实验系统，探究精细空间尺度下环境与地理因素何者主导真菌群落组成的构建。该系统由两组亲缘关系较远但同属的孤立松树配对组成，每对植株间以及与林缘的距离各不相同，借此可分离地理距离、宿主与土壤环境对关联真菌群落的影响效应。研究通过ITS扩增子的Illumina测序鉴定真菌群落组成，为每棵松树测定了树龄、体量与土壤化学性质等全部相关环境参数，并计算了每棵植株与其他所有个体以及最近林缘之间的地理距离。本研究采用广义差异模型分析，测试总真菌群落与外生菌根真菌（ectomycorrhizal fungi, EMF）群落的构建主要受地理因素还是环境过滤主导。研究结果提供了强有力的证据：与多数其他生物类群一致，真菌群落组成的更替同时显著受生态位与中性过程调控，但在精细空间尺度下，环境过滤对自由生活与共生真菌群落的构建均起主导作用。在本实验系统中，总土壤真菌群落的环境过滤主要受pH与有机质含量调控；而外生菌根真菌群落组成的核心影响因子为pH与阳离子交换量——令人意外的是，宿主物种并非其主要驱动因素。本研究结果支持新兴范式：pH可能在所有土壤介导的生态系统群落组装过程中发挥核心作用。