Many ecosystem functions depend on the availability of resources such as water and nutrients. In many ecosystems, rainfall patterns are changing and nutrient inputs are increasing. Microbial communities along with their associated plant communities might be able to respond and adapt rapidly to these changes in resource availability, causing changes to the overall functioning of the ecosystem. Increased decomposition, for example, might lead to loss of carbon stored in soil. Here, we test whether long term elevated rainfall and nitrogen lead to increased enzymatic activities in soils. To do this we compared hydrolytic and oxidative enzyme activities of soils that had received 10 years of elevated rainfall, elevated nitrogen or both. After this, we tested whether the history of rainfall and nutrient inputs would alter the ability of these communities to respond to extreme drought. To do this, we simulated a 1 in a 100 years drought on the plots using rainout shelters. We collected soils from the plots three times in the growing season to estimate enzyme activities.
Results/Conclusions
To our surprise, we found that hydrolytic enzyme activities were lower in plots with elevated rainfall, and regardless of nitrogen addition. This was true for the four enzymes we tested (B- glucosidase, Glucanase, B-N-acetylhexaminide, Phosphatase). It is important to point out that our site is predicted to experience greater mean annual precipitation, so our rainfall manipulation greatly increases the size of a rainfall event. Additionally, the sandy soils in our site tend to drain very quickly. Because of this, microbial biomass could be lower if resources become scarcer with large rainfall events and might explain the low enzyme activities we observed. Understanding how these microbial communities and their associated plant communities respond to these global changes is important as they play an important role in the carbon balance of ecosystems.