Changes in soil enzymatic activity in a P-limited Mediterranean shrubland subject to experimental nitrogen deposition

Abstract N deposition is a key driver of global environmental change (GEC). The effects of N addition on soil enzymes which play a key role in biogeochemical cycles and functioning of terrestrial ecosystems remain unclear, especially in vulnerable ecosystems such as P- or/and water-limited Mediterranean ecosystems. Here, we studied seasonal effects of N deposition on the activities of five soil extracellular enzymes in a semi-arid, P-deficient Mediterranean shrubland, and the association with physical and nutritional soil variables. Over the study period N deposition caused direct effects on soil enzymatic activities due to N-accumulation that increased its availability and triggered ecosystem mobilization of less available nutrients, such as P, in accordance with optimum allocation theory. N deposition intensified P limitation, enhanced the activity of phosphatases and reduced the activity of N- and C-mobilizing enzymes; it is likely this could lead to a longer term increase in soil C storage, due to a reduction in soil organic matter decomposition. The prompt response of soil enzyme activity to experimental N deposition indicates the high vulnerability of soil biogeochemical processes in this Mediterranean shrubland if submitted to prolonged N deposition.