Impacts of increased nitrogen deposition and altered precipitation regimes on soil fertility and functioning in semiarid Mediterranean shrublands

We studied the impacts of nitrogen (N) deposition and precipitation gradients on soil chemistry and functioning of calcareous soils from semiarid Mediterranean shrublands. Under greenhouse conditions, N fertilization at 0, 10, 20 and 50 kg N ha−1 yr−1 and low water increased inorganic N. The concentration of extractable cations was higher under low water due to reduced leaching, whereas soil carbon (C) to N ratio was affected by the interaction of N fertilization and water supply, suggesting the role of rainfall in the response of soil C and N storage capacity to N deposition. Soil phosphatase activity increased with N as a consequence of an induced N to phosphorus imbalance, whereas N-fixation was down-regulated by N fertilization, a response attributed to high levels of nitrate. Net N mineralization and nitrification were also reduced by N fertilization. Under field conditions, N availability was positively related to the N deposition gradient (3.98–6.05 kg N ha−1 yr−1). Nutrient availability was primarily and positively related to rainfall and temperature, although N deposition contributed to an overall cation depletion. Finally, we suggest the importance of conducting additional studies on the effects of N deposition and climate change on calcareous soils in Mediterranean ecosystems.