Soil microbial community responses to long-term land use intensification in subtropical grazing lands

Land use intensification often results in modification in plant cover and nutrient inputs with subsequent potential effects on composition and structure of soil microbial community and fractions. The objective of this study was to understand the long-term (> 22 yr) impacts of land use intensification (introduction of productive vegetation type, greater N fertilizer input and stocking rate) on soil microbial community composition and activity in Florida grazing lands. Experimental sites consisted of a gradient of management intensities ranging from native rangeland (lowest), silvopasture (intermediate), to sown pasture (highest). Increasing management intensity from native rangeland to sown promoted microbial biomass and activity. At the 0-10 cm, soil microbial biomass carbon (MBC) concentration was greater in sown pasture (334 mg kg− 1) compared to silvopasture and native rangeland (193 and 232 mg kg− 1, respectively). Similarly, potentially mineralizable C (PMC) increased in response to grazing land intensification (1.2 mg CO2-C kg− 1 d− 1 for sown pastures vs. 0.5 and 0.6 mg CO2-C kg− 1 d− 1 for native rangeland and silvopasture, respectively). Sown pastures exhibited the greatest levels of β-glucosidase activity (203 nmol g− 1 soil h.− 1) and phospholipid fatty acid (PLFA) biomass (222 μmol kg− 1 soil) compared to native rangeland and silvopasture. Results also demonstrated greater relative abundance of bacteria and less fungi as land use intensification increased from native rangeland to silvopasture or sown pasture. Our study indicated that long-term land use intensification affected the size, activity, and composition of soil microbial community in subtropical grazing lands.