Effects of soil water content, temperature and experimental nitrogen deposition on nitric oxide (NO) efflux from semiarid shrubland soil

Abstract

Southern Californian urban shrublands are exposed to high nitrogen (N) deposition, which can potentially enhance soil nitric oxide (NO) efflux; however, environmental controls on NO emission are still uncertain. We conducted a laboratory experiment to evaluate the NO efflux response of chaparral soil to variations in N availability, temperature and moisture. We hypothesized that NO efflux would increase with N addition, have an optimum response to soil moisture, and increase exponentially with temperature. Our results supported our hypotheses. Nitrogen addition caused a linear increase in NO efflux, primarily because of an increase in NH4+. NO efflux reached a peak at intermediate soil moisture (25% water-filled pore space (WFPS)), and the temperature response of NO flux was well-described by the Arrhenius model. However, there were statistically significant interactions between N, temperature and soil water content, making the NO response complex. Our results suggest that southern California urban shrublands may be important sources of NO, and that chronic, high levels of anthropogenic N deposition will enhance NO efflux from these ecosystems.