Dominance of arbuscular mycorrhizal fungi is key for Mongolian steppe management under livestock grazing, as indicated by ecosystem multifunctionality

Abstract

Livestock grazing of drylands supports millions of livelihoods worldwide; however, overgrazing causes severe biodiversity loss and degrades ecosystem functions. Understanding the effects of grazing intensity, aridity, and soil microbes is required for sustainable management. Here, we focused on arbuscular mycorrhizal (AM) fungi in soils and roots and examined their relationship with ecosystem multifunctionality under livestock grazing of Mongolian grasslands with different aridity levels. Above- and below-ground plant biomass were used to measure ecosystem-service multifunctionality, excluding annual plants that are unfavorable for ecosystem function and rangeland management. In both mountain forest steppe (mean annual precipitation = 207.7 mm) and steppe–desert steppe transition zone (mean annual precipitation = 128.4 mm), ecosystem multifunctionality was decreased by livestock grazing, as indicated by palatable plant shoot biomass. In line with the multifunctionality, the dominant plant species, Stipa krylovii, and AM plant biomass were decreased by livestock grazing. The Berger–Parker dominance index of soil AM fungi and Simpson’s diversity had a positive and negative relationship with multifunctionality, respectively, indicating that dominant AM fungi rather than AM fungal diversity in soil are key for maintaining multifunctionality. Root and soil AM fungal communities were significantly different with dominance of Rhizophagus operational taxonomic units (OTUs) in roots and Claroideoglomus OTUs in soil. However, the similarity between soil and root AM fungal communities increased with livestock grazing. Correlation analysis between palatable plant biomass and relative abundance of dominant AM fungal OTUs identified indicator virtual taxa that decreased (VTX00325 in roots, and VTX00165, VTX00214, and VTX00222 in soil) or increased (VTX00100, VTX00130, and VTX00295 in soil) with grazing intensity. The OTUs that were increased by grazing may be r-selected, grazing-tolerant AM fungi that accept a low C supply and supply few nutrients to plants. Our results suggest that grassland management focusing on ecosystem-service multifunctionality via control of AM plants, including S. krylovii and their co-dominant dominant AM fungi, in ungrazed grasslands are key for sustainable rangeland management in Mongolia.