Ectomycorrhizal fungal communities in relation to stand productivity and drought response in mature European beech forests

Mycorrhizal fungi form symbiotic relationships with trees and play a crucial role in tree growth, nutrition, and tolerance to environmental stress. Although numerous studies have shown that mycorrhizal fungi enhance nutrient and water uptake and increase tree resilience to drought, most evidence is derived from pot experiments, while comprehensive field-based studies in forest ecosystems remain scarce. Here, we test whether ectomycorrhizal fungal community composition can predict stand-level biomass productivity, tree nutritional status, and tree responses to severe drought. To address this question, we studied 60 mature European beech stands in Austria located along natural gradients of climate and nutrient availability. Soil samples were collected from the organic layer and mineral soil at depths of 0–10, 10–20, and 20–50 cm. DNA and ergosterol were extracted for fungal community and biomass analyses. Ectomycorrhizal community composition will be assessed using ITS2 amplicon sequencing, followed by bioinformatic processing to assign fungal taxonomy and guilds. These data will be related to stand biomass increment, leaf and soil nutrient data, as well as drought response indices derived from dendrochronological tree-ring analysis. This integrative approach allows us to disentangle the relative importance of ectomycorrhizal community composition and site conditions for forest productivity and drought response.