Glomalin and soil health: current understanding, ecological functions, and research frontiers

Glomalin-related soil proteins (GRSP) are operationally defined soil fractions associated with arbuscular mycorrhizal fungi (AMF) and are widely studied for their contributions to soil structure, carbon dynamics, and ecosystem functioning. Since its discovery, GRSP has attracted considerable attention because of its association with soil aggregation, carbon stabilization, and ecosystem sustainability. Glomalin, has been associated with various soil attributes, including the stability of soil aggregates, the size of soil carbon and nitrogen reservoirs, the sequestration of heavy metals, and the mitigation of diverse plant stresses. While GRSP concentrations in soil have often been correlated with AMF biomass measured through alternative (microscopic) methods, the chemical composition of GRSP extracted from soil remains intricate and not fully understood. This complexity arises from the nonspecific nature of its extraction and purification processes, as well as the diverse array of analytical techniques employed thus far to evaluate it. Current evidence suggests that GRSP contributes to soil organic carbon stabilization primarily through its association with soil aggregates. In this review, we endeavor to synthesize and explore various facets of glomalin, encompassing its composition, production mechanisms, soil-related functions, recalcitrant properties, and its potential role in the sequestration and stabilization of soil carbon.