Soil Microbial Activity with Depth in Claypan Soils of Southeast Kansas.

Extracellular enzymes mediate biogeochemical cycles in soils, but most studies of extracellular enzyme activity have only focused on the nutrient-rich surface soil layers. The importance of subsoil for the nutrient acquisition by plants and microorganisms is poorly characterized. Moreover, changes in biological properties of claypan soils are still unknown. The goal of this study was to determine changes in extracellular enzyme activity as a function of depth in claypan soils and across different land management practices (conventional tillage crop production, no-till crop production, and grassland). Soil cores were collected from three land management practices to a depth of 70 cm in Southeast Kansas on Parsons silt loam soil. Potential activities of two C-degrading enzymes (α-glucosidase, β-glucosidase), two N- degrading enzymes (N-acetyl glucosaminidase, L-aminopeptidase), one organic phosphorus- degrading enzyme (acid phosphatase), and two oxidases (phenol oxidase, peraoxidase) were measured at five depth intervals from the soil cores. We used phospholipid fatty acid (PLFA) analysis to assess microbial biomass and community structure. Overall, enzyme activity decreased with depth except for N-acetyl glucosaminidase, which showed constant activity with depth. All enzyme activities increased in soils at 30-60 cm. This may be due to changes in the soil texture and clay content. Enzyme activities were highest in the grassland soil, followed by the no-till soil. The conventional tillage soil had the lowest enzymatic activities, especially near the surface. Our study indicates that low-carbon subsoils contain small but metabolically active microbial communities, and that differences in enzymatic activity may be a good method of monitoring management practices to develop improved soil health.