长白山原始林和次生林土壤有效氮含量对模拟氮沉降的响应

Responses of Soil Available Nitrogen of Natural Forest and Secondary Forest to Simulated N Deposition in Changbai Mountain

研究了长白山地区阔叶红松林和杨桦次生林生长季土壤有效氮(铵态氮+硝态氮)含量及其在高氮(50kg.hm-2.a-1)、低氮(25kg.hm-2.a-1)处理下的变化状况。结果表明:生长季内,两种林型土壤有效氮含量具有明显的季节变化特征。二者土壤铵态氮在研究期内均呈现先减少后增加再减少的变化趋势,而硝态氮在林型中的变化趋势不同:杨桦次生林中先减小后增加再减小;阔叶红松林中则呈减小的趋势,生长季末略有增加。杨桦次生林和阔叶红松林土壤有效氮的生长季总平均值分别为6.83和6.80mg·kg-1,其中铵态氮分别占45.36%和33.30%,硝态氮占54.64%和66.70%。两种林型土壤总有效氮、铵态氮和硝态氮含量对不同氮沉降梯度的响应大致相同,表现为随氮沉降量的增加而增加,其中高氮处理显著增加了土壤中的铵态氮、硝态氮及总有效氮的含量(P<0.05),但这种促进效果在低氮处理下则不明显(P>0.05)。

An experiment was conducted to study the variation of soil available nitrogen （ NH4^＋-N and NO3^- --N ） in growing season and the effect of nitrogen deposition on soil available nitrogen in bread-leaved Korean pine forest and secondary poplar and birth mixed forest in Changbai Mountain. Two N treatments, high N （50kg·hm^-2·a^-1） and low N （25kg·hm^-2·a^-1） were established in two forests. Results showed that the content of soil available nitrogen in the two forests exhibited obvious seasonal variation in growing season. The content of NH4^＋ --N in the two forests decreased first, then increased and finally decreased again, while the changing tendencies of NO3^- --N were different in the two forests. In the secondary poplar and birth mixed forest, the changing tendency of NO3^- -N was similar to that of NH4^＋ -N. However, the content of NO3^- -N in the broad-leaved Korean pine forest showed a decrease tendency and only increased a little at the end of the growing season. The average available nitrogen contents of the secondary poplar and birth mixed forest and the broad-leaved Korean pine forest were 6.83 and 6.80 mg·kg^-1 in the growing season, of which, ammonia nitrogen （NH^4＋ -N） accounted for 45.36 percent and 33.30 percent, and nitrate nitrogen （NO3^- --N） accounted for 54.64 percent and 66.70 percent, respectively. The responses of soil available nitrogen, NH4^＋ -N and NO^3- --N to N deposition were approximately consistent in the two forests and all of them increased with increasing N deposition. The contents of soil available nitrogen, NH4^＋ -N and NO3^- -N increased under the treatment of high-N（P 〈 0.05 ）, however, the effect of Low-N treatment was not significant（P 〉 0. 05 ）.