Moss biocrusts sustain snowpack and soil function in cold deserts

Snow cover serves as a critical component of cold deserts, providing a sustained source of available water over time. Biocrusts largely cover soils in deserts, yet their role in regulating snowpack ablation remains largely unknown. Here we conducted a multiyear, in situ and continuous experiment to evaluate the effects of moss-dominated biocrusts on the depth and duration of snow cover, along with their consequences for soil moisture, microbial richness (bacteria and fungi) and soil respiration (carbon efflux). Compared with bare soil, our long-term measurements revealed that moss biocrusts greatly extended snow cover duration by 20.1% (65 h) and enhanced mean snow depth by 27.1%. These effects were associated with the influences of biocrusts on surface roughness and thermal conductivity, which further contributed to greater snowmelt, leading to 16.0% higher water content and up to a 46.1% increase in microbial richness beneath biocrusts compared with nearby bare soils. Furthermore, soil carbon efflux driven by microbial respiration was up to 33.5% higher under biocrusts compared with bare soils. Our study suggests that moss biocrusts play an important role in supporting biological activity and ecosystem function in cold deserts under global warming by moderating snow cover dynamics.