[Responses of soil carbon and nitrogen mineralization to nitrogen deposition in tundra zone of the Changbai Mountain, China.]

The alpine tundra ecosystem, with low soil inorganic nitrogen (N) availability, has a weak buffer against nitrogen and is susceptible to exogenous N enrichment. Here, with a laboratory incubation experiment, we investigated the response of soil carbon and nitrogen mineralization to N deposition with soil samples from the tundra zone on the northern slope of the Changbai Mountain. We set three N levels, control (CK, 0 kg·hm ^-2 ), low N (N ₁ , 25 kg·hm ^-2 ), and high N (N ₂ , 50 kg·hm ^-2 ), with N being added as NH ₄ NO ₃ . The results showed that N addition had no significant effect on soil C mineralization rate, but significantly affected the accumulation of soil C minera-lization. The N ₂ treatment inhibited soil C mineralization. After the 40 d incubation, soil inorganic N content increased with increasing N addition. After the 80 d incubation, soil inorganic N content in the N ₂ and N ₁ was similar and significantly higher than that of CK. Those results indicated that N addition promoted soil N mineralization. The soil microbial biomass C and N in the N ₁ was higher than that in the N ₂ and CK, indicating that low N input had stronger effects on soil microbial activity. Increasing N deposition might accelerate C and N turnover in the tundra soils and enhance the soil inorganic N content. While it could provide more N for plants, it may increase the risk of N loss.