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.

尽管真菌在森林碳（C）循环中发挥关键作用，且学界呼吁将微生物相互作用纳入生态系统模型，但真菌功能群（fungal guild）丰度的变化如何影响土壤碳库，迄今仍未得到充分量化，尤其是在大多数碳储存的矿质土壤（mineral soils）中。此外，为更全面地解析土壤碳动态，学界仍需更深入理解真菌不同功能群间的相互作用如何调控地下凋落物分解。本研究在温带针叶林（temperate coniferous forest）中开展实验发现，壕沟断根处理（experimental trenching）降低了外生菌根真菌（ectomycorrhizal fungi）与腐生真菌（saprotrophic fungi）的丰度比值，同时使土壤碳库减少10%，这一现象主要源于表层5 cm土层内颗粒态有机质（particulate organic matter）的降低。壕沟断根处理还促进了表层土壤中根系与真菌凋落物的分解。综合来看，本研究结果支持了这一长期被提出但极少得到验证的假说：真菌功能群丰度变化可促进土壤碳固存。不过，研究结果同时表明，该效应可能仅对土壤表层的短期碳储存最为显著。