Trade-off between soil organic carbon sequestration and plant nutrient uptake in arbuscular mycorrhizal symbiosis

Arbuscular mycorrhizal fungi (AMF) play a pivotal role in soil organic carbon (C) dynamics. AMF can channel C obtained from plants into the soil as labile and recalcitrant materials with contrasting impacts on soil organic carbon (SOC) reserves. Labile C supply, while increasing microbial biomass, can also elevate microbial respiration, leading to enhanced organic matter turnover. Conversely, the production of recalcitrant materials, including biomass and glomalin-related soil protein (GRSP) can promote SOC sequestration directly by acting as long-term C storage, strengthening soil aggregates, and promoting the formation of mineral-bound organic carbon. The contrasting impacts of AMF products on SOC often generate controversies regarding the role of AMF communities in C capture, especially under rising atmospheric CO₂ concentrations. Emerging evidence suggests that distinct AMF phylogeny exhibit varying soil organic matter mobilization and symbiotic nutrient exchange abilities owing to their divergent life histories. However, we argue that resource use efficiency among AMF species significantly influences the phenotypic outcome of AM symbiosis, as well as their impacts on soil carbon dynamics. AMF functional traits favoring recalcitrant C substances including glomalin-related proteins and mineral-associated organic matter over labile C may positively impact SOC sequestration in the long-term. Whereas an AMF functional guild promoting plant growth through labile C (i.e., sugars) exudation may increase SOC turnover leading to lead to SOC loss. Although strong mutualist AMF may negatively impact SOC stocks, they can compensate for this trade-off by depositing fresh, newly fixed C and promoting plant photosynthesis. The ways in which this trade-off is offset can vary among different AMF species and community compositions, warranting further investigation.