Ericaceous shrub encroachment influences the structure of soil fungal communities in subalpine grasslands

Abstract

Shrub encroachment influences fungal communities, but detailed knowledge of this influence missing. Using DNA metabarcoding, measure of plant functional traits, soil properties and laccase activities, we studied soil fungal communities along an ericaceous shrub encroachment gradient in two similar subalpine sites (Stubai, Austria and Lautaret, France) that differ in their shrub composition. Fungal taxonomic richness, driven by evergreen shrub cover and soil P, was 1.4 times lower in Stubai than Lautaret. Shrub density affected community taxonomic turnover only at Lautaret, with a qualitative change between 32 % and 63 % cover. Across sites, soil parameters were the primary determinants of fungal community turnover, along with shrub cover, herbaceous biomass and plant functional traits related to tissue quality. At Stubai, fungal community turnover responded to Calluna vulgaris cover, community weighted mean (CWM) lignin and soil properties (P, pH). In contrast, at Lautaret, the change in fungal community composition between low and high shrub cover was significantly explained by shrub cover, herbaceous biomass, plant traits (community-level C:P and herbaceous leaf dry matter content: LDMC) and soil pH. These differences in fungal community turnover translated to varying abundances of fungal functional groups between and within sites. In particular, high shrub cover was associated with a sharp decrease (12 times less) in ectomycorrhizal fungi and a sharp increase (1.3 times more) in saprophytes. Soil laccase activities were low and constant in Stubai, not exceeding 60 nmol. Min⁻¹. μg protein⁻¹ but were higher and decreased with increasing shrub density, from 281 to 125 nmol. Min⁻¹. μg protein⁻¹ at Lautaret. Our study demonstrates a significant impact of shrub functional composition on fungal communities, related to shrub density and functional traits associated with tissue quality. Such changes are expected to alter the biogeochemical functioning of subalpine grasslands.