Effects of rainfall amount and frequency on soil nitrogen mineralization in Zoigê alpine wetland

Abstract Changes in rainfall patterns can affect the soil nitrogen (N) cycles. Most studies have focused on the effect of the amount of rainfall, but the effect of the frequency of rainfall has rarely been considered. In this study, we conducted a field experiment in the Zoige alpine wetland that examined two levels of the amount of rainfall, i.e. 100% or 70% of the natural amounts of rainfall. In addition, we examined three frequencies of rainfall events. First was the natural interval, while the second and third were increases of 50% and 100% of the inter-rainfall dry periods based on the natural interval of the rainfall events, respectively. We found that the amount and frequency of rainfall had significant interactive effects on N mineralization, and thus influenced the concentration of mineral N in the Zoige alpine wetland. The reduction of the rainfall amount significantly increased N mineralization rate, NO3−-N concentration and mineral N stock in the high frequency treatment, and N mineralization rate, decreased them in the low frequency treatment. The variation of the soil NH4+-N, NO3−-N, and mineral N stock increased with the reduction in the rainfall frequency and the increase in the soil depth. Thus prolonged drought (low frequency of rainfall) and reduced rainfall due to future climatic change may decrease the mineral N concentration and N mineralization rate in Zoige alpine wetland, which may probably have a profound impact on the alpine wetland ecosystem.