庐山毛竹扩张及模拟氮沉降对土壤N_2O和CO_2排放的影响

Effects of Moso Bamboo (Phyllostachys edulis) Expansion and Simulated Nitrogen Deposition on Emission of Soil N_2O and CO_2 in Lushan Mountain

毛竹是我国南方广泛分布的一种典型的森林资源,其扩张已引发了多方面的生态问题,但是目前关于氮沉降背景下毛竹扩张引起的土壤N_2O和CO_2气体排放变化的研究甚少,且无原位观测数据。采用静态箱-气相色谱法,分析江西庐山毛竹纯林、毛竹扩张形成的毛竹-日本柳杉混交林及日本柳杉纯林3种林分土壤的N_2O和CO_2排放速率和累积排放量及其对模拟氮沉降的响应。结果表明:(1)混交林土壤的NH_4^+-N含量、NO_3^--N含量及pH分别为14.39mg·kg^(-1)、8.65mg·kg^(-1)、4.88,显著高于日本柳杉纯林的9.75 mg·kg^(-1)、5.58 mg·kg^(-1)、4.05,但是混交林土壤DOC含量(236.5 mg·kg^(-1))却显著低于日本柳杉纯林(382.0mg·kg^(-1))。(2)混交林土壤N_2O累积排放量(393.6mg·m^(-2))显著高于毛竹纯林(202.5mg·m^(-2))和日本柳杉纯林(192.8mg·m^(-2)),混交林土壤CO_2累积排放量(4 655 g·m^(-2))显著高于日本柳杉纯林(2 815 g·m^(-2))。(3)模拟氮沉降未对3种林分类型土壤的CO_2排放速率和累积排放量产生显著影响,但明显增加了混交林和日本柳杉纯林的N_2O累积排放量。本研究表明:毛竹扩张不同阶段土壤的理化性质、N_2O及CO_2排放表现出不同特征。毛竹扩张过程中一定程度上增大了土壤N_2O和CO_2的排放量,但是完全扩张后N_2O排放出现明显下降趋势,而CO_2的排放未发生显著变化。同时,氮沉降促进了毛竹未扩张和扩张初期土壤的N_2O排放,而对CO_2排放未产生显著影响。表明在未来气候变化条件下管理亚热带毛竹扩张时,必须明确考虑这些生态系统组成、结构和影响因子之间的影响。

【Objective】Moso bamboo is a typical type of forest resource widely distributed in South China. Its expansion, however, has caused a number of ecological problems, especially emission of soil N2 O and CO2 in the groves as affected by nitrogen deposition, which has rarely any research papers, let alone insitu field observation data.【Method】In this study, the static chamber technique was used to monitor N2 O and CO2 emission rates, cumulative N2 O and CO2 emissions and their responses to simulated nitrogen deposition in pure moso bamboo forest, moso bamboo-Japanese cedar mixed forest and pure Japanese cedar forest in Lushan Mountain, Jiangxi Province.【Result】Results show:(1) the content of NH4+-N, content of NO3--N,and pH in the mixed forest soil was 14.39 mg·kg-1, 8.65 mg·kg-1, and 4.88, respectively, significantly higher than their respective ones in the Japanese cedar forest soil(i.e. 9.75 mg·kg-1, 5.58 mg·kg-1 and 4.05), but the former(236.5 mg·kg-1) was much lower than the latter(382.0 mg·kg-1) in DOC content;(2) the cumulative N2 O emission in the mixed forest(393.6 mg·m-2) was significantly higher than that in the moso bamboo forest(202.5 mg·m-2) and that in the Japanese cedar(192.8 mg·m-2), while the cumulative CO2 emission in the mixed forest(4 655 g·m-2) was significantly higher than that in the Japanese cedar forest(2 815 g·m-2);and(3) simulated nitrogen deposition had no significant effect on CO2 emission rate and cumulative CO2 emission in the three types of forest soils, but significantly increased cumulative N2 O emission in the Japanese cedar forest soil and mixed forest soil. 【Conclusion】All the findings indicate that the soils varied in physicochemical property and N2 O and CO2 emission characteristics with the expansion of moso bamboo. Expansion of moso bamboo did increase N2 O and CO2 emission from the soils to a certain extent. However, when the expansion completed, like in the moso bamboo forest, emissions of N2 O decreased significantly, while emission of CO2 did not change much. Meanwhile, nitrogen deposition promoted N2 O emission from the Japanese cedar forest soil(no bamboo intruding) and the mixed forest soil(early stage of moso bamboo expansion), but had no significant effect on CO2 emission. It is, therefore, suggested that in management of moso bamboo expansion in subtropical China under future meteorological conditions, it is essential to take into account effects of composition and structure of the ecosystem and other various affecting factors.