Biological soil crusts structure the subsurface microbiome in a sandy agroecosystem

Abstract

Biological soil crusts (biocrusts) are commonly found in semi-arid ecosystems and complete biological nitrogen (N) fixation, build soil carbon (C) stocks, and increase soil moisture. Biocrusts were recently identified in Florida agroecosystems, and based on traits of semi-arid biocrusts, could contribute to crop growth and soil health. This study determined the influence of biocrusts in a Florida citrus orchard on microbial diversity and composition of surface and crop root zone soil as related to soil C, N, and moisture. Soil samples were collected from areas with biocrust and proximate bare soil (control) in a Florida, USA, citrus orchard. Cores were divided into three soil depths, and soil bacterial and fungal communities were characterized using the 16S rRNA gene and ITS region sequences, respectively. Biocrust presence and sampling depth significantly impacted microbial community composition. Cyanobacteria and heterotrophic diazotrophs had low relative abundances compared to copiotrophic bacteria in the biocrust soil. Soil below biocrusts had increased moisture, nutrient concentrations, and relative abundances of nitrifying bacteria compared to the root zone below bare soil. Copiotrophic bacteria were enriched under biocrusts, indicating potential for nutrient competition between roots and microorganisms. Biocrust subsoil had elevated relative abundances of Ascomycota and Basidiomycota which contributed to higher fungal community richness and evenness in the rooting zone. Biocrust subsoil had increased relative abundances of microbiota compared to bare soil without biocrusts, potentially influencing nutrient cycling, crop nutrient uptake and growth, and soil health.