The role of glomalin in mitigation of multiple soil degradation problems

There is a direct link between the increasing human population and soil degradation that raises current and future food security concerns. Soil amelioration using beneficial microorganisms, particularly arbuscular mycorrhizal fungi (AMF), is essential and pragmatic. AMF produces glomalin that also contributes to the mitigation of soil degradation. However, studies on the ecological role of glomalin are scattered and patchy, and no evident overview exists. We fill this knowledge gap by a systematic and comprehensive literature review of the glomalin's role in the context of soil degradation problems, including soil desertification, fertility loss, and pollution. Glomalin improves soil physical properties, carbon sequestration, nutrient contents, microbial activities, stabilizes pollutants, and eventually assists ecological restoration. Such a positive impact of glomalin is thought to be through its prevailing impact on soil; by acting as a substrate for microbes, a gluing agent for aggregate formation, chelation of heavy metals and toxic pollutants, and improving carbon sequestration through long-term persistence (>= 42 years) in soil. Given the production of glomalin as a result of an interplay between plant, soil, and AMF, hence, we provide specific strategies at the plant, soil, and microbial level to improve glomalin concentration. Specifically, we can develop genetically modified or hybrid plants for higher rhizodeposition and promotes soil microbial diversity through the inoculation of AMF and beneficial bacteria. We highlight the research gaps and discuss prospects. This knowledge will improve our understanding of glomalin, stimulate future research, and be useful for the sustainable restoration of degraded lands.