重庆缙云山三种典型林分穿透水和树干茎流中氮素特征研究

Nitrogen Characteristics in Throughfall and Stemflow in Three Typical Forests on Jinyun Mountain, Chongqing City

为研究重庆酸雨区森林生态系统中氮湿沉降在不同林分中的分布特征,以重庆缙云山为站点,于2012年5月到10月间,测定了针阔混交林、常绿阔叶林和毛竹林三种典型林分内大气降水、穿透雨和树干茎流的铵态氮(NH4+-N)、硝态氮(NO3--N)和可溶性有机氮(DON,Dissolved Organic Nitrogen)浓度,并进行系统分析。结果表明:(1)各林分降雨组分中氮浓度均值关系为:NH4+-N>NO3--N>DON,NH4+-N和NO3--N的最小值分别为1.84 mg L-1和1.11 mg L-1,而DON浓度不超过0.47 mg L-1;(2)相比于大气降水,各林分的穿透雨和树干流的氮浓度都有增加,林分上分布表现为:针阔混交林>常绿阔林>毛竹林;(3)在时间尺度上,各林分穿透雨NH4+-N和NO3--N浓度的最高值、次高值和最低值分别出现在10月份、8月份和6月份,林分间差异不显著。树干茎流无明显时间分布规律,林分间无显著差异。研究指出,降雨量不是决定氮浓度的关键因子,而林分对氮浓度的影响作用显著。

To investigate the distribution characteristics of wet nitrogen deposition in different stands within the acid rain area of the forest ecosystem in Chongqing, field observation is carried out in Jinyun Mountain in from May to October 2012. Concentrations of NH4+-N, NO3--N and DON(dissolved organic nitrogen) resolved in precipitation,throughfall and stemflow are collected in evergreen broad-leaved forest, mixed wood forest and Phyllostachys,respectively, and then are systematically analyzed. Results show as follows.(1) The concentration order of nitrogen wet deposition observed in three hydrologic processes and the three stands is NH4+-N>NO3--N> DON. The minimum values of NH4+-N and NO3--N are 1.84 mg L-1and 1.11 mg L-1, respectively, while the maximum of DON content is only 0.47 mg L-1.(2) Nitrogen contents in throughfall and stemflow are comparably larger than that of precipitation,and orders as mixed wood forest> evergreen broad-leaved forest > Phyllostachys.(3) As for the temporal scale, the first and second highest concentration values of NH4+-N and NO3--N in throughfall occur in October, August, and June,respectively, without significant differences among the different stands. Nevertheless, contents of nitrogen in throughfall don't follow the above law, and non-significant difference exists neither. It is pointed in this research that precipitation is not a critical factor affecting nitrogen concentration, while the significant influences of stands on nitrogen concentration cannot be ignored.