Effects of grazing and fire management on rangeland soil and biocrust microbiomes

Biocrusts play important roles in rangeland ecosystems by protecting soil surfaces and fixing carbon and ni-trogen. Their responses to rangeland management practices, however, are poorly understood. Here, we char-acterised the impacts of cattle grazing and fire management (controlled 2-or 4-yearly burning versus no fire) on the diversity and composition of biocrust and associated soil bacterial communities (0-1 cm depth) in a long-term (30-60 years) field experiment in the Northern Territory, Australia. Both experiments were replicated on two soil types (vertosol, calcarosol). For the grazing experiment, we also characterised samples from 0 to 10 cm depth. Significant effects of grazing on bacterial community composition were only detected in the vertosol, where it was generally associated with enrichments of cyanobacterial taxa in the 0-1 cm samples, and more varied responses in 0-10 cm samples. In contrast, despite some minor reductions in the relative abundances of Bacillus populations in more frequently burned sites (late season 2-yearly burning), we did not observe any significant impacts of fire management on the overall composition of bacterial communities. Our findings indicate that the presence of livestock in rangelands increases the proportional representation of cyanobacteria within biocrust and associated soil microbiomes, and that these communities, at least from a taxonomic perspective, are not strongly impacted by fire management.

Automated summary

Biocrusts play important roles in rangeland ecosystems. This study investigated the impacts of cattle grazing and fire management on the diversity and composition of biocrust and associated soil bacterial communities. The results showed that grazing had significant effects on bacterial community composition, particularly in one soil type, while fire management did not have significant impacts on bacterial communities. The findings suggest that livestock presence increases the proportional representation of cyanobacteria in biocrust and associated soil microbiomes, and fire management does not strongly affect these communities from a taxonomic perspective.