Mycorrhizal association shapes responses of plant biomass but not soil carbon to nitrogen addition in global forests

Abstract

Mycorrhizal association regulates plant nutrient uptake and productivity, thereby shaping soil carbon storage capacity in terrestrial ecosystems. Ectomycorrhizas (EcM) and arbuscular mycorrhizas (AM) are two widespread mycorrhizal types, with distinct nutrient economy. However, how different mycorrhizal strategies affect responses of aboveground biomass (AGB) and soil organic carbon (SOC) to nitrogen (N) inputs in forests remains unclear. To address this issue, we compiled a global dataset of plant productivity and SOC responses to N addition, encompassing 262 forest sites dominated by trees associated with AM and EcM. In the AM forests with inorganic economy, exogenous N inputs substantially stimulated aboveground plant-derived biomass (+35.4 %), contributing to an accumulation of SOC (+5.5 %). This was partly linked to microbial growth and metabolite formation. In contrast, in the EcM forests with organic economy, fertilization resulted in SOC accrual (+6.0 %) via an increase in AGB (+13.3 %) and an inhibition of microbial decomposition (-11.4 %), with the latter effect strengthening at higher addition rates. Our findings demonstrate that N fertilization divergently influences plant biomass and soil carbon accumulation in forests with distinct mycorrhizal strategies, underscoring that integrating mycorrhizal-specific managements can enhance fertilization effectiveness and carbon sequestration of forest ecosystems.