Soil responses to climate change in drylands: impact of aridity on extracellular enzyme activities

Climate change is causing an increasing aridification in the existing drylands worldwide, through increasing temperatures and changing precipitation patterns, and drylands areas are projected to expand. Drylands are particularly fragile ecosystems where climate change drivers are expected to affect the ecosystem functioning, altering soil properties and biogeochemical cycles. We focused on extracellular enzyme activities (EEAs) as they are a key parameter to evaluate soil functioning, since they’re involved in nutrient cycling; in particular, we addressed 4 hydrolytic enzymes involved in carbon, nitrogen and phosphorus cycles. We followed two approaches in parallel: (i) we measured potential EEAs along a natural aridity gradient including humid, dry-subhumid and semi-arid environments in Portugal; (ii) we carried out climate manipulation treatments to simulate the projected changes in average temperatures and amount of precipitation. We found that all the enzymes measured showed a decreasing pattern along the aridity gradient, probably due to the progressive reduction in soil water content and increasing soil temperature. The climate manipulation treatments did not show a significant effect on EEAs at a regional scale, except for Phosphatase, which showed a differential response along the Aridity gradient, with the differences decreasing at higher Aridity levels. We suggest that long-term effects still have to be investigated.