Microbial communities and enzymatic activities under different management in semiarid soils

Information about the size, composition and ecological role of soil microorganisms remains unknown for some semiarid regions of the world while soil functioning and productivity depend on its biological component. This study evaluated the microbial communities and enzyme activities of C, N, P and S cycling in representative soils (0–5 and 5–15 cm) of the semiarid region of Puerto Rico as affected by management and land use. Soil organic C (OC) at 0–5 cm was higher under pasture (2–3-fold) and mango (Mangifera indica) trees (1.6-fold) compared to vegetable production, and similar in vegetable production (average for four soils: 15.8 g kg−1 soil) and quenepas (Melicoccus bijugatus) trees (15.9 g kg−1 soil). Soil microbial biomass C (MBC = 167–1401 mg C g−1 soil) was higher in soils under trees (up to 2.4-fold) and pasture (>2.5 times at both depths) compared to vegetable production. Similar trends were found for soil MBN among the systems. Principal Component Analysis (PCA) showed differences in the soil microbial community structure under pasture and trees due to higher fungal FAME markers (i.e., 18:2ω6c, 18:1ω9c, 16:1ω5c and 18:3ω6c) compared to agricultural soils under vegetable production. Unique FAMEs for soils under pasture were: 20:4ω6c, 18:1ω5c, 14:1ω5c, 11Me18:1ω7c, 15:1ω6c and i15:1. Higher number of fatty acids was extracted (51–55) from soils under pasture than in vegetable production (36–45). Several enzymatic activities (i.e., β-glucosaminidase, β-glucosidase, alkaline phosphatase and different pools of arylsulfatase) were higher (up to 4-fold) in soils under pasture, and under trees compared to the vegetables production soils. Differences found in the soil microbial community and enzymatic activities among systems have potential to be reflected in the soil functional integrity and ecosystem services, and should be considered when altering land uses to less conservative practices in the region studied.