Shifting Fungal Guild Abundances Change Temperate Coniferous Forest Soil C Stocks

Despite the importance of fungi to forest carbon (C) cycling and calls to include microbial interactions in ecosystem models, how shifting fungal guild abundances impact soil C stocks remains poorly quantified, particularly in mineral soils where most C is stored. Additionally, a greater understanding of how fungal interguild interactions affect belowground litter decomposition is needed to more fully characterize soil C dynamics. In a temperate coniferous forest, we found that experimental trenching reduced ectomycorrhizal:saprotrophic fungal ratios and concurrently decreased soil C stocks by 10%, due mainly to decreased particulate organic matter in the top 5 cm. Trenching also stimulated both root and fungal litter decomposition in surface soils. Together, these results support the often proposed but rarely tested hypothesis that shifting fungal guild abundances promote soil C accumulation. However, they suggest this effect may be most relevant for short-term C storage in upper soil layers.