氮添加和凋落物去除对黔中喀斯特地区柳杉人工林土壤呼吸的影响

凋落物是土壤呼吸的主要碳源,日益增加的大气氮沉降通过改变森林凋落物的输入与分解影响土壤呼吸。为揭示氮沉降及凋落物管理对森林土壤呼吸及其组分的影响,以贵州省国有扎佐林场15年生柳杉人工林为研究对象,设置4个氮添加处理:对照(CK,0 gN m^-2 a^-1)、低氮(LN,15 gN m^-2 a^-1)、中氮(MN,30 gN m^-2 a^-1)和高氮(HN,60 gN m^-2 a^-1),并在每种氮添加处理下设置去除凋落物和保留凋落物两种处理,于2021年3月-2022年2月利用LI-8100测定土壤呼吸速率,并分析氮添加及凋落物处理对土壤呼吸速率影响,确定影响土壤呼吸速率变化的主要因子。结果表明:氮添加和去除凋落物处理没有改变土壤呼吸速率的时间变化,土壤呼吸速率月均最大值出现在7月,月均最小值出现在2月。氮添加对土壤呼吸速率无显著影响(P > 0.05),除CK外,去除凋落物处理会显著降低土壤呼吸速率(P < 0.05)。凋落物对土壤总呼吸速率的贡献率为8.6%-28.5%,且LN处理下凋落物对土壤呼吸速率的贡献率最大。土壤呼吸速率与5 m土壤温度呈显著指数相关(P < 0.01),与5 cm土壤湿度呈显著负线性相关(P < 0.01)。土壤温度解释了土壤呼吸速率变异的58.5%-79.5%,土壤湿度解释了土壤呼吸速率变异的26.4%-39.5%,以土壤温度和湿度构建的双变量模型拟合效果均好于单因子模型,土壤温湿度共同解释土壤呼吸速率变异的59.1%-85.8%。结论表明在大气氮沉降增加的背景下,温度是影响土壤呼吸的主要因素,凋落物管理是调控土壤呼吸的关键过程。

Effects of nitrogen addition and litter removal on soil respiration of Cryptomeria fortunei plantation in Karst Area of central Guizhou Province

Litter is the main carbon source for soil respiration. Soil respiration rate is affected by increasing atmospheric nitrogen deposition which through changing the input and decomposition of forest litters. To reveal the effects of nitrogen deposition and litters management on soil respiration rate, a 15-years old Cryptomeria fortunei plantation was selected as the research object in state-owned Zhazuo forestry farm of Guizhou Province. Four nitrogen addition treatments were set up in the Cryptomeria fortunei plantation, which were Control plots (CK,0 gN m^-2 a^-1), low nitrogen plot (LN, 15 gN m^-2 a^-1), medium nitrogen (MN, 30 gN m^-2 a^-1) and high nitrogen (HN, 60 gN m^-2 a^-1), respectively. Meanwhile, litter removal and litter control group (no litter treatment) were designed in each nitrogen addition treatment. Soil respiration rate were measured by Li-8100 from March 2021 to February 2022. The effects of nitrogen deposition and litter treatments on soil respiration rate were analyzed based on the measured data, and the main influence factor was determined according to the analysis. The results showed that the temporal variations of soil respiration rate were not influenced by nitrogen addition and litter removal, the maximal monthly values of soil respiration rates all appeared in July and the minimal monthly values all appeared in February among different nitrogen addition treatments. Nitrogen addition had no significant influences on soil respiration rate (P > 0.05), whereas litter removal decreased soil respiration rate significantly (P < 0.05) except CK plot. The contributions of litter to total soil respiration rate were 8.6%-28.5% in different nitrogen addition treatments, and the largest contribution of litter appeared in LN plot. There were significant exponential relationship between soil temperature and soil respiration rate at 5cm soil depth in all nitrogen addition levels, and 58.5%-79.5% variations of soil respiration rate were explained by soil temperature model. The soil respiration rate showed significant negative linear relationships with soil moisture at 5cm soil depth in all nitrogen addition levels, and changes of soil respiration rate could be interpreted 26.4%-39.5% by soil moisture. The determination coefficient of the bivariate model based on soil temperature and soil moisture was larger than single factor model, and 59.1%-85.8% variations of soil respiration rate were explained by the bivariate model in all nitrogen addition plots. It is conclude that temperature is the main factor affecting soil respiration rate, and litter management is the key process to regulate soil respiration under the background of increasing atmosphere nitrogen deposition.