Compost additions decrease relative abundance of biocrust cyanobacteria and alter soil stable isotope signature

Abstract Compost amendments are a promising tool for building productivity in degraded rangelands, but the effect on biological soil crusts (biocrusts), the surface microbial communities found in drylands, has not been investigated. Biocrusts contribute both carbon uptake and other ecosystem services in drylands. We investigated how 6.3 mm of surface-dressed compost at a Tribal rangeland in central New Mexico, USA, affected temperature, carbon and nitrogen characteristics, the relative abundance of biocrust microbial communities (fungi and bacteria) – specifically cyanobacterial communities – as well as the resulting aggregate stability at the soil surface after 1 year. Surface temperature maxima increased with compost addition in cooler ambient conditions, and the δ13C signatures of the soils from compost addition plots were >1‰ lighter compared to controls, indicating >35% of soil carbon was compost-derived, but organic C, total N percentage and aggregate stability did not differ among compost treatments. Several compost-derived taxa became indicator species in the amended plots, and compost addition decreased cyanobacteria relative abundance up to 58%. While previous results show that compost may benefit plants from a slow-release fertilization effect and soil carbon in deeper soil layers increases, there could be complex impacts on biocrust organic carbon with changing temperature and microbial community.