氮添加对亚热带常绿阔叶林土壤有机碳及土壤呼吸的影响

以福建省武夷山亚热带常绿阔叶米槠林为研究对象, 开展氮添加实验。采用4个氮添加梯度(CK, N50, N100和N150, 分别表示氮添加0, 50, 100和150 kg/(hm²·a))模拟自然氮沉降变化, 探究氮添加对土壤有机碳及土壤呼吸的影响。结果表明, 氮添加对表层土壤(0~20 cm)总有机碳的影响不显著, 对颗粒态有机碳(POC)和矿物结合态有机碳(MAOC)两种不同碳组分含量的影响不同。其中, N100和N150处理分别使土壤POC含量显著上升110.7%和147.9% (p₁ = 0.024, p₂ < 0.001); 土壤MAOC含量则随氮添加量升高呈下降趋势, 但差异不显著。土壤呼吸速率的年际波动呈单峰式, 且在不同观测时间内, 各样地土壤呼吸速率对氮添加的响应不同。通过土壤呼吸速率与土壤温度的拟合方程计算, 得到2018—2020年CK, N50, N100和N150样地土壤呼吸年均碳排放量分别为1205.31, 1191.56, 1287.56和1128.61 g C/m²。其中, N50样地与CK样地无显著差异, N100样地显著上升6.82% (p<0.001), N150显著下降 6.8% (p<0.001), 即N100可以促进土壤呼吸年碳排放, 而N150对土壤呼吸年碳排放有抑制作用。

Effects of Nitrogen Addition on Soil Organic Carbon and SoilRespiration in Subtropical Evergreen Broad-Leaved Forest

In order to simulate changes in natural nitrogen deposition and explore the effects of nitrogen addition on soil organic carbon and soil respiration, four treatments (CK (control), N50 (50 kg/(hm²·a) of N), N100 (100 kg/(hm²·a) of N) and N150 (150 kg/(hm²·a) of N)) were conducted in a subtropical evergreen broad-leaved forest in Wuyi mountain, Fujian Province. The results showed that the effect of nitrogen addition on the TOC of the surface soil (0–20 cm) was not significant, and the effect on the content of its different components is different. Compared to the CK, N100 and N150 significantly increased the soil POC content by 110.7% and 147.9% (p₁ = 0.024, p₂ <0.001). The content of soil MAOC tended to decrease with the increase of nitrogen addition, but the difference was not significant. The annual dynamic of soil respiration rate was unimodal distribution, and nitrogen treatments had different effects on soil respiration in different observation time. Based on fitting equations of soil respiration rate and soil temperature, the annual average carbon efflux of soil respiration in CK, N50, N100, and N150 plots from 2018 to 2020 were 1205.31, 1191.56, 1287.56 and 1128.61 g C/m², respectively. Compared to the CK, annual average carbon efflux of soil respiration did not change significantly in N50, significantly increased by 6.82% in N100 (p<0.001), and significantly reduced by 6.8% in N150 (p<0.001), which meaned that N100 promoted annual carbon efflux from soil respiration, while N150 had an inhibitory effect on it.