氮沉降对杉木人工林土壤呼吸与土壤纤维素酶活性的影响

为研究森林土壤呼吸速率和纤维素酶活性对氮沉降增加的响应,以福建三明沙县官庄林场12年生杉木人工林为研究对象,设置了N0、N1、N2和N3四个水平,N沉降量以氮素计依次为0、60、120、240 kg.hm-2.a-1,对其林地土壤表层(0-20 cm)、中层(20-40 cm)和底层(40-60 cm)土壤进行了为期3 a的模拟氮沉降试验。结果表明:氮沉降抑制了林地表层土壤的呼吸作用,但明显促进了中层和底层土壤的呼吸作用。在N1、N2和N3处理下,林地表层土壤呼吸速率分别降低了28.34%、2.04%和15.31%,而中层土壤土壤呼吸速率分别增加了53.44%、62.22%和20.20%,底层土壤呼吸速率分别增加了117.46%、42.72%和72.86%。氮沉降在初始的2 a内使森林土壤纤维素酶活性提高,而在第3年,N1和N2处理对土壤纤维素酶活性的促进作用减弱,N3处理则显著降低了土壤纤维素酶活性。总体上看,经N1、N2处理后,土壤呼吸速率与土壤纤维素酶活性存在正相关性,而N3处理下两者的关系不显著。

Impacts of nitrogen deposition on the soil respiration rate and soil cellulose enzyme activity in Chinese fir plantation

Nitrogen deposition significantly impacts the forest ecosystems structure and function,but few researches about it have been reported in China.To investigate the response of soil respiration rate and soil cellulose anzyme activity to increased nitrogen deposition in the forest,a field experiment was conducted in a 12-year-old Chinese fir plantation in Sanming,northwestern Fujian.Nitrogen loadings were designed at 4 levels as N0,N1,N2,and N3,at the doses of 0,60,120 and 240 kg·hm-2·a-1,respectively,with 3 replicates in each treatment.Based on 3 years of manipulation,nitrogen loading was found to inhibit soil respiration rate in the 0-20 cm depth,but promote respiration rate in the 20-60 cm horizon.N1,N2 and N3 treatments decreased surface soil respiration rates by 28.34%,2.04% and 15.31%,respectively,but increased soil respiration rate by 53.44%,62.22% and 20.20% within the 20-40 cm depth,respectively,and by 117.46%,42.72% and 72.86% at the soil depth of 40-60 cm,respectively.In the first 2 years of treatment,nitrogen deposition was observed to elevate soil cellulose enzyme activity,but in the third year the magnitude of enhancement declined in N1 and N2,and significant inhibition was detected for N3.Significant positive linear relationship was developed between soil respiration rate and soil cellulose anzyme activity in the treatments of N1 and N2,but insignificant in N3.