Urbanization and Grazing Impact on Mesquite Phyllosphere and Soil Microbial Communities

Abstract

Dryland degradation driven by human activities, particularly associated with urban and grazing land use types, has been shown to result in an overall loss of biodiversity above and below the soil surface. The modification of microbial community dynamics by these degrading processes can result in ecosystem changes that could potentially lead to the proliferation of invasive species, changes in biogeochemical cycling, and injury soil and plant health. This study attempts to investigate the impacts of urban and grazing land use types on the soil and phyllosphere microbiome associated with velvet mesquite (Prosopis velutina). The goal of this research was to analyze differences in the above and belowground microbiomes that are specific to urban or grazing land use types to potentially identify microbial trends associated with land degrading processes. Soil and phyllosphere samples were collected from three land use types including natural, urban, and grazing (light and heavy pressures). Soil bacterial/archaeal communities did not demonstrate significant differences across locations, but soil fungal richness and diversity was significantly lower in urban locations. However, urban phyllosphere exhibited greater average microbial richness and Shannon diversity than natural or grazing locations. Heavy grazing pressure resulted in lower soil fungal diversity, but fungal richness was not significantly different between grazing pressures. Inferred microbial functional group proportions showed that urban soils had the lowest average proportion of nitrogen fixers and cellulolytic microorganisms, but the greatest average proportion of fungal plant pathogens. Light grazing pressure exhibited a significantly greater proportion of soil arbuscular mycorrhizal fungi. The phyllosphere of urban locations had the greatest average proportion of nitrogen fixers and locations with heavy grazing pressure demonstrated the greatest proportion of phyllosphere fungal plant pathogens and cellulolytic microorganisms.