Effects of C:N imbalance on soil microbial physiology in subtropical tree plantations associated with ectomycorrhizal and arbuscular mycorrhizal fungi

Abstract

• ECM plantations had a greater C:N imbalance than AM plantations; • ECM plantations had a marginally lower microbial CUE than AM plantations; • ECM plantations had higher specific C- and N-acquisition enzymes than AM plantations; • C:N imbalance mediated the variations in microbial physiology between mycorrhizal types. Although the effect of different mycorrhizal types on the soil carbon (C) and nitrogen (N) cycles has been studied intensively, the mismatch between the C:N stoichiometry of microorganisms and their resources (i.e., C:N imbalance) and its impact on microbial physiology remain unclear. In this study, we measured the C:N imbalance, microbial C use efficiency (CUE), and C- and N-acquisition enzyme activities in four tree plantations associated with ectomycorrhizal (ECM) or arbuscular mycorrhizal (AM) fungi in subtropical China. We found that the C:N imbalance in ECM plantations was 44% higher than that in AM plantations, which was associated with the lower microbial CUE and higher specific C- and N-acquisition enzyme activities. Collectively, from a novel perspective of ecological stoichiometry, our results demonstrate that the C:N imbalance and the microbial physiological activities it mediated differ between ECM- and AM plantations which have important knock-on consequences for soil C sequestration in the subtropical forests.