A spatiotemporal framework reveals contrasting factors shape biocrust microbial and microfaunal communities in the Chihuahuan Desert

Biocrusts harbor soil-surface communities composed of autotrophic and heterotrophic microbiota that affect nutrient cycling, plant performance, soil hydrology and stability within drylands. Biocrust community composition is mostly thought to be driven by abiotic factors, but the structure of the bacteria, fungi, protist, and microfauna taxa are rarely documented simultaneously or over time. In this study, we examined the composition, abundance, and diversity of microbes (bacteria and fungi) and microfauna (protists and microscopic microfauna) in three types of biocrusts among two different vegetative habitats in the northern Chihuahuan Desert during three successive seasons. Microbial groups were identified by phospholipid fatty acid analyses (PLFA) and included actinobacteria, other gram-positive bacteria, other gram-negative bacteria, rhizobia arbuscular mycorrhizal fungi, and saprophytic fungi. Microfauna were enumerated via microscopy and included nematodes, tardigrades, rotifers, amoebae, ciliates, and flagellates. We found that microbial communities were most affected by biocrust type, whereas microfaunal communities were more influenced by sampling season. Season was also associated with different indicator taxa. Additionally, microbial communities were related to biocrust chemical properties—which changed with season and surrounding vegetation—while microfaunal communities were not. In cyanolichen-dominated crusts, but not others, the structure of microbial and microfaunal communities were strongly correlated. Our study highlights possible food web interactions and provides evidence that the co-occurring microbial and microfaunal taxa associated with biocrusts are temporally dynamic and structured by different drivers.