Data from: Ectomycorrhizal fungal richness declines toward the host species’ range edge

Plant range boundaries are generally considered to reflect abiotic conditions; however, a rise in negative or decline in positive species interactions at range margins may contribute to these stable boundaries. While evidence suggests pollinator mutualisms may decline near range boundaries, little is known about other important plant mutualisms, including microbial root symbionts. Here we used molecular methods to characterize root associated fungal communities in populations of two related temperate tree species from across the species’ range in the eastern United States. We found that ectomycorrhizal fungal richness on plant roots declined with distance from the center of the host species range. These patterns were not evident in non-mycorrhizal fungal communities on roots, nor in fungal communities in bulk soil. Climatic and soil chemical variables could not explain these biogeographic patterns, although these abiotic gradients affected other components of the bulk soil and rhizosphere fungal community. Depauperate ectomycorrhizal fungal communities may represent an underappreciated challenge to marginal tree populations, especially as rapid climate change pushes these populations outside of their current climate niche.

植物分布边界通常被认为反映非生物环境条件；然而，分布边缘处物种负相互作用的增强或正相互作用的减弱，或许是促成这些稳定分布边界的因素之一。尽管已有证据显示传粉者互利共生关系在分布边界附近可能减弱，但学界对其他重要的植物互利共生关系（包括根系微生物共生体）的了解仍十分有限。本研究针对美国东部两种近缘温带树种的种群，利用分子方法对其根系相关真菌群落进行了表征，采样覆盖了两个物种的整个分布范围。研究发现，植物根系上的外生菌根真菌（ectomycorrhizal fungi）物种丰富度随其与宿主物种分布中心的距离增加而降低。上述模式在根系的非菌根真菌群落以及非根际土壤（bulk soil）的真菌群落中均未显现。尽管气候与土壤化学变量能够影响非根际土壤和根际（rhizosphere）真菌群落的其他组成部分，但它们无法解释上述生物地理模式。外生菌根真菌群落的物种贫乏化，或许是边缘林木种群面临的一个未被充分重视的挑战，尤其是在快速气候变化正迫使这些种群脱离其当前气候生态位的背景下。