Soil fungal biomass and nitrogen cycling in European beech stands

Fungi are a major component of soil microbial communities in forest ecosystems and regulate a wide range of biogeochemical processes. Saprotrophic fungi decompose dead organic matter, pathogenic fungi can influence plant fitness, and symbiotic mycorrhizal fungi support plant nutrient acquisition in exchange for photosynthetically derived carbon. Beyond their functional diversity, fungal biomass represents a substantial pool of soil organic carbon through living fungal tissues and extensive mycelial networks. Soil fungi further interact with other microbial groups, thereby influencing nutrient turnover and overall ecosystem functioning. Here, we investigate how forest stands differ in soil fungal biomass and which environmental parameters best predict variability in fungal biomass. We further test how net nitrogen mineralization, a process often associated with bacteria-dominated nitrogen transformations, relates to fungal biomass. Soil samples were collected from 60 mature European beech stands distributed across the Vienna Woods, Austria. Fungal biomass was estimated by quantifying ergosterol concentrations extracted from soil samples taken from the organic layer and from three depths in the mineral soil (0–10, 10–20, and 20–50 cm). Net nitrogen mineralization rates were determined by measuring ammonium and nitrate concentrations before and after a 12-day laboratory incubation. Fungal biomass was related to nitrogen mineralization rates as well as a wide range of stand-, soil-, and site-level variables. First results are presented and discussed in the context of soil carbon storage and nitrogen availability.