Lower carbon fractions and microbial carbon use efficiency in ant-mound surface soils than in adjacent biocrusted soils of a revegetated desert

Drylands are key components of the global carbon cycle, and biological soil crusts (biocrusts) are important secondary groups of primary producers. Ants are among the most abundant soil-dwelling animals in drylands; however, the relationship between ant nesting activity and the surface soil carbon cycle in biocrust systems remains unclear. In a revegetated area of the Tengger Desert, we compared five surface (0–5 cm) microhabitats (ant-mound soil, the biocrust and soil beneath mounds, and adjacent control biocrust and soil) in terms of physicochemical properties, 12 carbon fractions, 13 C-glucose-based microbial carbon use efficiency (CUE), and greenhouse-gas fluxes under standardized laboratory incubation. Compared with the control surface soil, ant-mound soils exhibited significantly lower water content, pH, and nutrient content, as well as a coarser texture. Mound soils also contained significantly less soil organic carbon (−62%), microbial biomass carbon (−63%), and labile fractions (e.g., particulate organic carbon − 69% and easily oxidizable carbon − 66%), as well as a significantly lower microbial CUE (0.305 vs. 0.418; −27%). During incubations, intact biocrust plus its underlying soil acted as a net CH 4 sink (−2.9 to −3.7 µg C kg −1 d −1 ), whereas mound and exposed surface soils were net CH 4 sources (+3.2 to +4.8 µg C kg −1 d −1 ); N 2 O efflux was higher in mound soil than in control surface soil, although control biocrust showed comparably high N 2 O. Because ant nest sites are not chosen at random, we interpret these contrasts as associations that may arise from nest construction, pre-existing site differences, or both. Ant mounds occupy only approximately 0.12% of the surface; therefore, their contribution to landscape-scale fluxes is small; the principal finding is a consistent surface-soil contrast showing that ant nesting is associated with lower near-surface carbon storage and microbial carbon-use efficiency in biocrust-covered drylands. Explicitly accounting for such faunal surface disturbance would improve assessments of biocrust carbon accrual in dryland restoration.