UC Riverside

Future climate projections predict a global increase in precipitation variability as well as a trend towards aridity, which can influence how nitrogen (N) is cycled in terrestrial ecosystems. Increasingly arid conditions can alter N cycling by increasing soil inorganic N concentrations and making this N more susceptible to loss. Further, shifts in precipitation patterns in one season can establish effects on the N cycle that can “carry-over” into the following season, known as precipitation legacy effects. However, how current and historic precipitation patterns may alter soil N availability through changes in inorganic N supply—i.e., gross N mineralization and gross nitrification—is not well constrained. We measured the effects of altering precipitation variability on soil N cycling using an isotope pool dilution on soils from a Pinyon–Juniper dryland under a precipitation manipulation experiment. We found that wintertime drought, the most extreme drought we imposed, reduced gross N mineralization by ~2.5x and gross nitrification rates by ~9.5x compared to ambient conditions, establishing a legacy effect that reduced gross N mineralization by ~2x compared to ambient conditions the following summer. As we observed an increase in soil N concentrations (~6x greater than ambient conditions) simultaneous with lower gross rates of inorganic N supply under drought, our results imply that dry conditions must have reduced N immobilization rates below those of inorganic N supply to account for the increased N availability. Our measurements show that extreme drought can have negative consequences on inorganic N supply that persist even after the drought ends, suggesting these responses may become more common as drought is expected to increase in frequency and severity across the globe.