Fungal-mediated soil aggregation as a mechanism for carbon stabilization

Soils can potentially be turned into net carbon sinks for atmospheric carbon to offset anthropogenic greenhouse gas emissions. Occlusion of soil organic carbon (SOC) in soil aggregates is a key mechanism which temporarily protects it from decomposition by soil organisms. Filamentous fungi are recognized for their positive role in the formation and stabilization of aggregates. In this review we assess the current knowledge of the contribution of fungi to soil aggregation, and set a new research agenda to quantify fungal-mediated aggregation across different climates and soils. Our review highlights three main knowledge gaps: (1) the lack of quantitative data and mechanistic understanding of aggregate turnover under field conditions, (2) lack of data on the biochemical and biological mechanisms by which filamentous fungi influence soil aggregation, and (3) uncharacterized contribution of soil fungi across environments. Adopting a trait-based approach to increase the level of mechanistic understanding between fungal diversity and soil structure seems promising, but will need additional experiments in which fungal diversity is manipulated by either removal through sieving or dilution, or addition through using synthetic communities of cultured fungi. We stress the importance of integrating ecological and physicochemical perspectives for accurate modeling of soil aggregation and SOC cycling, which is needed to successfully predict the effects of land management strategies.