Arbuscular Mycorrhizal Fungi Promote Soil Respiration Primarily Through Mediating Microbial and Root Biomass in Rocky Desertification Habitat

Arbuscular mycorrhizal (AM) fungi can have complicated interactions with plants and soils, which play a critical role in mediating the soil carbon cycle. However, the mechanism by which AM fungi regulate soil respiration is not well documented. This study conducted a completely randomized block-design mesocosm experiment using the inoculation of AM fungi (RI: Rhizophagus intraradices; FM: Funneliformis mosseae) with Fraxinus malacophylla to identify the pathways of AM fungi controlling soil respiration in a rocky desertification habitat. We observed that the average soil respiration rates (3.78 μmol·m−2·s−1) were significantly higher in two AM fungi inoculation treatments than in the control (2.87 μmol·m−2·s−1). Soil respiration rates were 1.59-fold higher in RI fungi inoculation and 1.05-fold higher in FM inoculation than in the control. Explanation rates of microbial biomass carbon, biomass nitrogen, and root biomass in RI (57.46–76.49%) and FM (44.81–62.62%) inoculation for soil respiration variation were higher than those in the control (24.51–34.32%). The direct positive pathway of soil respiration was mainly regulated by microbial biomass (59.5%) and root biomass (34.90%), while the indirect positive contributions of soil physicochemical properties (30.00%), colonization level (3.50%), soil microclimate (19.30%), and enzyme activity (3.38%) to respiration dynamics ranked second. Thus, we conclude that soil respiration dynamics can be mainly controlled by AM fungi-mediated changes in microbial and root biomass in rocky desertification areas.