EFFECTS OF SNOWPACK AND LITTER DECOMPOSITION ON NITROGEN DYNAMICS IN SOIL OF THE ALPINE ZONE OF THE EASTERN TIBETAN PLATEAU

Microbes remain active and play an important role in soil nitrogen (N) cycle during the winter in soil of the alpine zone. A shift from microbial N immobilization process dominant during summer to prevailing microbial mineralization process during the winter is observed. Warmer soil under deep snow cover may increase the microbial activity and rate of organic matter decomposition over the winter. Furthermore, severe shortages of dissolved carbon (C) in the winter may cause microbial mortality and lyses. Thus, C limitation on microbial growth and activity may have an important effect on winter N mineralization and even on soil N pools. However, the combined effects of additional organic C (litter inputs) and snow cover on soil N biogeochemical processes in the Tibetan Plateau remain unclear. In the current study, the in situ effects of snow-pack and litter decomposition on N dynamics in the alpine zone of the Eastern Tibetan Plateau were investigated. Intact soil core incubations in three different snow regimes (0, 30 and 100 cm depth snow) in the winter were used to solve the problem by measure concentrations of mineral form of soil N. In addition, the litter bag method was used to analyze the litter decomposition over the winter. Our results indicate that the snow cover reduced the ammonium (NH4+-N) content, accelerate N mineralization in soil, and did not significantly change the dissolvable organic nitrogen (DON) and microbial biomass nitrogen (MBN). Meanwhile, snowpack increased the litter N content and accelerated litter decomposition in late winter. Litter addition reduced the MBN and NH4+-N contents in soil, but increased the nitrate (NO3--N) content and net N mineralization, suggesting that N availability to plants during the spring thaw period may be enhanced.