Soil microbial response to altered precipitation regimes at the Sevilleta National Wildlife Refuge, New Mexico

Microbes substantially control many biogeochemical processes in semiarid systems, including carbon and nitrogen fixation and carbon mineralization. Bacteria and fungi are osmotrophs that release enzymes into the environment to generate assimilable carbon and nutrients from organic particles. These enzymes are also the first agents to respond to pulses of soil moisture. The capacity to stabilize extracellular enzymes on soil particles preserves the utility of these nutrient-generating agents during extended dry periods. Enzyme stability can relate to environmental conditions and increase with clay mineral and humic compound concentrations. To better understand microbial response to precipitation variability, our objective was to determine the stability of extracellular enzymes under various monsoon precipitation regimes. During summer 2010, soil enzyme activity was measured in a rainfall manipulation study within a mixed-grass semiarid grassland in New Mexico, USA. Plots received either one large rain event or three evenly spaced small rain events per month. Before and after the first rain of each month, soil samples from the rhizosphere and from interspaces between plants were collected and analyzed for activity of four hydrolases; beta-glucosidase, beta-N-acetylglucosaminidase, leucine aminopeptidase, and alkaline phosphatase.