Continuous microhabitats as crossroads of fungal communities in a primeval temperate forest

Abstract

Forests represent the largest terrestrial ecosystem on Earth, covering about 30% of its surface, and their microbial inhabitants carry out crucial ecosystem processes. Forests comprise a wide variety of microhabitats including soil, litter, living trees and dead wood. Forest fungi can form hyphal networks within or across such microhabitats in search of nutrients, and translocate plant-derived carbon from roots to soil. Various drivers affect their occurrence, such as climate and the presence of competing species. Drivers and predictors of fungal diversity at the fine scale of a forest stand composed of a range of microhabitats are, however, much less clear than those operating at larger scales. The aim of this study is to determine what best captures the heterogeneity of fungal communities in a 5000 m2 mixed forest stand in the temperate natural forest Žofín using a metabarcoding survey of the ITS2 region of fungal rRNA across seven microhabitats: soil, litter, fine roots, senescent leaves, twigs, branches and dead trees. We assessed the impact of microhabitat patchiness as well as the predictive power of niche and neutral processes in shaping fungal diversity and community structure within and across microhabitats. Environmental filters such as phosphorus content, carbon/nitrogen ratio and pH were significant predictors of fungal community composition between microhabitats. Contrastingly, fungal communities displayed significant spatial patterns only in soil, litter and roots, i.e. continuous microhabitats. When focusing on pairs of samples collected at the same approximate location, continuous microhabitats displayed a higher similarity, on average, between themselves and other microhabitats, as opposed to semi-continuous and patchy microhabitats. As the ultimate sink of organic matter, soil harbored the highest number of recurrent fungal units from other microhabitats, emphasizing that not only does soil collect debris across the forest floor, but it also acts as a crossroad where locally abundant fungi collide.