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Despite the importance of fungi to forest carbon (C) cycling and increasing calls to include microbial interactions in ecosystem models, how shifting fungal guild abundances impact soil C stocks re- mains poorly quantified, particularly in mineral soils where most C is stored. Additionally, a greater understanding of how fungal interguild interac- tions affect belowground litter decomposition is needed to more fully characterize soil C dynamics. To address these knowledge gaps, we conducted a multi-year soil trenching experiment in two tem- perate Pinus strobus stands in Minnesota, USA. We found that after two years, trenching increased ectomycorrhizal fungal relative abundance while decreasing saprotrophic fungal relative abundance (decreased ectomycorrhizal/saprotrophic ratio) and concurrently decreased soil C stocks by 10%. The decreased C stocks were primarily due to changes in particulate organic matter and were largely constrained to the top 5 cm of the soil. Trenching also stimulated both root and fungal litter decom- position 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 also suggest this effect may be most relevant for short- term C storage in upper soil layers.