摘要
高山苔原生态系统的土壤无机氮含量较低,对氮的缓冲性弱而易受外源氮输入的影响.本研究以长白山北坡苔原带土壤为研究对象,通过室内培养试验,以NH_4NO_3为外加氮源,设置3个施氮水平:对照(CK,0 kg·hm~(-2)),低氮(N_1,25 kg·hm~(-2)),高氮(N_2,50 kg·hm~(-2)),分析长白山苔原带土壤碳、氮矿化对氮沉降的响应.结果表明:氮添加处理对长白山苔原带土壤碳矿化速率影响不显著,但对土壤碳矿化累积矿化量影响显著,N_2抑制了土壤的碳矿化作用.培养40 d后,氮添加处理提高了土壤无机氮含量;而培养80 d后,N_2与N_1的无机氮含量差异不显著,但都明显高于CK,氮输入促进了土壤氮的矿化.培养过程中,N_1处理下的微生物生物量碳、氮高于N_2和CK处理,说明低氮输入对土壤微生物活性的促进作用更明显.在未来氮沉降增加的背景下,长白山苔原土壤碳、氮周转可能加快,提高土壤无机氮含量.土壤中无机氮含量增加,虽然可以为植物生长提供更多生长所需的氮素,但也提高了土壤氮素的流失风险.
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_4NO_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.
引文
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