Impacts of Precipitation Change and Nutrient Addition on Soil Enzyme Activities Across a Habitat Productivity Gradient.

Central to predicting how environmental changes will affect ecosystem services is understanding whether their impacts depend on soil type - does an environmental change consistently increase or decrease a service across soils, or do its impacts vary with soil properties? We addressed this question at a unique site where three very different soil types (serpentine gravel/sand, serpentine clay and non-serpentine loam) occur in close proximity. Since spring 2010, replicate plots on each soil have received late spring precipitation addition and NPK nutrient addition in a 2 x 2 factorial design. In spring 2013, potential activities of the following soil enzymes were measured: β-glucosidase (BG), β-N-acetylglucosaminidase (NAG), acid phosphatase (AP), polyphenol oxidase (PPO) and peroxidase (PER). Nearly all enzyme activities differed among soil types in the absence of environmental change treatments. Effects of precipitation addition depended on soil type, in a manner that was fairly consistent across enzymes. In contrast, effects of nutrient addition did not differ across soils - in all three soils, added nutrients increased activity of the hydrolytic enzymes involved in C and C+N acquisition (BG, NAG), while activities of the oxidative enzymes (PPO and PER) were unaffected. AP was unique in not responding to either treatment, although its activity did differ among soil types in a manner consistent with the other enzymes. Overall, we found that soil type mattered more for predicting the impacts of one environmental change (precipitation addition) than another (nutrient addition). In addition, one change (precipitation) affected most enzymes similarly, while another change (nutrients) had different impacts on different types of enzymes.