Moisture-mediated control of fungal necromass decay by ectomycorrhizal roots

Despite growing recognition that fungal necromass can significantly contribute to long-term soil organic carbon stocks, the relative importance of plant versus microbial control on fungal necromass decay remain poorly resolved. Recent work in ectomycorrhizal forests have reported faster fungal necromass decay when tree roots are severed, suggesting that ectomycorrhizal roots and fungi can decelerate fungal necromass decomposition. Because fungal necromass generally decomposes on the order of weeks, and ectomycorrhizal fungal growth and activity varies seasonally, the magnitude of this decelerating ectomycorrhizal effect on fungal necromass decay may also vary seasonally. Here, we tested whether ectomycorrhizal effects on fungal necromass decay depend on season and necromass quality using a replicated root trenching experiment in a temperate pine forest. Fungal necromass produced from Hyaloscypha bicolor was incubated as two necromass types differing in melanin content, used as a proxy for necromass quality (low vs. high), across three successive time periods in 2021 (May to June, July to August, and September to October). Ectomycorrhizal fungal abundance was quantified using sand-filled ingrowth bags combined with ITS2 high-throughput amplicon sequencing and fungal 18S qPCR.