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，在于厘清生态位过程（niche processes）与中性过程（neutral processes）何者为群落构建（community assembly）的核心驱动力量——前者如环境过滤（environmental filtering），后者如扩散限制（dispersal limitation）。本研究利用孤立林木"岛屿"这一天然实验系统，探究在精细空间尺度（fine spatial scales）下，环境抑或地理因素是真菌群落组成（fungal community composition）的主要构建因子。该实验系统包含成对隔离的两种亲缘关系较远的同属松树，它们以彼此间及与林缘（forest edge）间各不相同的距离被定植，借此我们得以厘清地理距离（geographic distance）、宿主（host）与土壤环境（edaphic environment）对关联真菌群落的影响效应。研究团队通过对ITS扩增子（ITS amplicons）进行Illumina测序（Illumina sequencing）以鉴定真菌群落组成，测定每株松树的全部相关环境参数，包括树龄（tree age）、植株体量（tree size）与土壤化学性质（soil chemistry），并计算每株松树与其余植株及最近林缘间的地理距离。本研究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调控。研究结果强有力地表明：与诸多其他生物类群一致，真菌的群落组成周转同时受到生态位过程与中性过程的显著调控，但在精细空间尺度下，环境过滤在自由生活真菌与共生真菌群落的构建中均占据主导地位。在本实验系统中，我们发现总土壤真菌群落的环境过滤主要由pH值与有机质含量驱动；而调控外生菌根真菌群落组成的核心因子为pH值与阳离子交换量（cation exchange capacity）——令人意外的是，宿主物种并未产生显著影响。本研究结果佐证了新兴范式：pH值或许在所有土壤介导的生态系统群落构建中发挥核心作用。