Arbuscular mycorrhizal dominated forests facilitate organic carbon stabilization in soil aggregates

Abstract Tree mycorrhizal association types play a pivotal role in soil carbon (C) accumulation. However, their effects on soil C stabilization remain controversial, and the mechanisms of how mycorrhizal types affect aggregate‐associated soil organic carbon (SOC) are poorly understood. To investigate how tree mycorrhizal associations affect aggregate‐associated SOC sequestration, we examined the soil aggregates, glomalin‐related soil protein (GRSP), soil respiration and microbial traits from samples collected in four arbuscular mycorrhizal (AM) and four ectomycorrhizal (ECM)‐dominated stands. Additionally, we conducted a 1‐year mixed‐litter incubation experiment to determine the effect of mycorrhizal type on these soil properties under controlled conditions. The results showed that AM‐dominated forests had 65.5% higher total aggregate‐associated SOC than ECM forests in the field, and that high‐quality AM litter increased it by 16.5% compared to low‐quality ECM litter in the incubation experiment. In both field and laboratory studies, the total SOC accrual was mainly from macroaggregate SOC changes, while GRSP and leaf chemical properties contributed most to the SOC variation. The path model indicated that AM tree species are positively and indirectly related to SOC through their associations with litter chemistry, GRSP, soil aggregate stability and microbial traits in the field study. Additionally, field data showed that soil microbial diversity and bacterial life strategies were associated with the SOC accrual in AM forests. Synthesis . Our findings highlight that AM‐dominated forests have higher aggregate‐associated SOC accrual through macroaggregate formation, along with higher litter quality, enhanced GRSP levels and shifts in soil microbial communities and life strategies. These findings contribute to deepening our understanding of soil C patterns in different mycorrhizal‐dominated forest ecosystems and offer critical insights for predicting and enhancing future forest C sinks.