Exploring the secrets of hyphosphere of arbuscular mycorrhizal fungi: processes and ecological functions

Background Most plants have a hyphosphere, the thin zone of soil around extraradical hyphae of arbuscular mycorrhizal (AM) fungi, which extends beyond the rhizosphere. This important interface has critical roles in plant mineral nutrition and water acquisition, biotic and abiotic stress resistance, mineral weathering, the formation of soil macroaggregates and aggregate stabilization, carbon (C) allocation to soils and interaction with soil microbes. Scope This review focuses on the hyphosphere of AM fungi and critically appraises the important findings related to the hyphosphere processes, including physical, chemical and biological properties and functions. We highlight ecological functions of AM fungal hyphae, which have profound impacts on global sustainability through biological cycling of nutrients, C sequestration in soil, release of greenhouse gas emissions from soil and the diversity and dynamics of the microbial community in the vicinity of the extraradical hyphae. Conclusions As a critical interface between AM fungi and soil, hyphosphere processes and their important ecological functions have begun to be understood and appreciated, and are now known to be implicit in important soil processes. Recent studies provide new insights into this crucial zone and highlight how the hyphosphere might be exploited as a nature-based solution, through understanding of interactions with the microbiome and the impacts on key processes governing resource availability, to increase sustainability of agriculture and minimize its environmental impact. Uncovering hyphosphere chemical and biological processes and their subsequent agricultural, ecological and environmental consequences is a critical research activity.