Microbial enzymatic response to reduced precipitation and increased nitrogen in a southern Californian grassland

Microbial enzymes play a fundamental role in ecosystem processes and nutrient mineralization and therefore understanding changes due to anthropogenic induced environmental alteration is vital. We measured extracellular enzyme activities in litter decomposing in plots with either reduced precipitation or increased nitrogen in a grassland ecosystem in Loma Ridge National Landmark in Southern California. We used a reciprocal transplant design to examine the effects of plot treatment, litter origin, and microbial community origin on litter decomposition and extracellular enzyme activity. Samples were collected in March and June 2011 and analyzed for the activities of cellobiohydrolase (CBH), β-­‐glucosidase (βG), α-­‐ glucosidase (αG), N-­‐acetyl-­‐β-­‐D-­‐glucosaminidase (NAG), β-­‐xylosidase (βX), acid phosphatase (AP), leucine aminopeptidase (LAP), polyphenol oxidase (PPO), and peroxidase (PER). For the precipitation treatment, carbon and phosphorus-acquiring enzymes increased their activity with reduced precipitation in the plot level manipulation, but decreased for the litter origin manipulation and showed few effects for the microbial origin manipulation. Nitrogen-acquiring enzymes produced mixed results with NAG increasing its activity and LAP decreasing its activity at the plot level manipulation for both March and June (p\u3c0.001, p\u3c0.001 for March and p\u3c0.001 for NAG in June). In the reduced water treatment, drier litter may have forced microbes to produce more enzymes to obtain necessary nutrient concentrations because of enzyme immobilization and lack of diffusion. Decomposition rates decreased despite increased activity, perhaps due to lower enzyme and substrate diffusion rates. Added nitrogen treatment effects were varied and minimal. Interactive effects in both the nitrogen-amended and precipitation-reduced treatments also produced few results