川中丘陵区桤柏混交林土壤温室气体排放与生态系统碳收支
文献类型：学位论文
| 作者 | 王小国
|
| 学位类别 | 博士 |
| 答辩日期 | 2007 |
| 授予单位 | 中国科学院水利部成都山地灾害与环境研究所 |
| 授予地点 | 成都 |
| 导师 | 朱波 |
| 关键词 | 桤柏混交林 土壤 温室气体 Forest-DNDC模型 异养呼吸 自养呼吸 碳收支 |
| 学位专业 | 自然地理学 |
| 中文摘要 | 全球变暖是人类所面临的最严峻的环境问题之一，并日益成为公众和科学界关注的焦点。研究表明，温室气体如CO2、CH4和N2O等在大气中浓度的上升是全球气候变暖的主要原因。温室气体的源汇失衡引起气候异常等一系列严重的问题，对人类生存和社会经济持续发展带来了巨大的威胁。近几十年来，中国政府积极推行天然林保护工程、退耕还林工程和大规模植树造林活动，使得我国森林覆盖率不断提高，人工林面积不断加大。同时，人工造林活动提供了一种降低CO2释放的潜在减缓措施，可用以抵消各国承诺的温室气体减排指标。川中丘陵区地处长江上游生态屏障的最前沿，具有特殊的生态敏感性，自20世纪70年代以来陆续营造了大面积的桤柏混交林。目前，桤柏混交林已成为长江上游防护林的主体模式。本文通过长期连续的野外定位观测和采样分析，结合Forest-DNDC模型模拟，研究川中丘陵区人工桤柏混交林土壤CH4、N2O和CO2三种主要温室气体以及土壤各分室呼吸排放特征、影响因素。对34yr人工桤柏混交林生物量和生产力进行了测定，计算了混交林生态系统植被碳库和土壤碳库，并估算了桤柏混交林生态系统碳收支大小。主要结论如下：(1) 桤柏混交林土壤温室气体排放具有明显的季节变化，均表现为夏秋季较高，而春冬季较低的特点。林地土壤是CO2和N2O的排放源，是CH4的一个吸收汇。林地土壤CO2和N2O的年平均排放通量分别为4892.8 kgC ha-1a-1和0.98 kgN ha-1a-1；CH4的年平均吸收通量为1.74 kgC ha-1a-1。地表凋落物的去除对林地土壤CO2和N2O排放有显著影响，但对CH4吸收的影响则不显著。(2) 林地土壤CO2排放温度敏感性指数(Q10值)存在明显的季节变化，其大小与土壤温度呈显著的负相关关系而与土壤湿度呈显著的正相关关系，关系式分别为：Q10 = -0.0835T + 3.4362(R2 = 0.67，n= 12，p<0.01)；Q10 = 0.1741W－2.4718(R2 =0.51，n =12，p< 0.01)。表明在测定的温度和湿度范围内，本地区土壤（5cm）处温度每升高1℃，Q10值将减少0.0835；土壤（0～10cm）湿度每升高1%，Q10值将增加0.1741。(3) 持续干旱对林地土壤温室气体的源汇功能产生了显著影响。干旱期间林地土壤CO2、CH4和N2O平均排放（吸收）速率与2005年同期相比均有不同程度的下降，其中对N2O排放的影响最大。(4) Forest-DNDC模型较好的模拟了桤柏混交林土壤CO2和N2O排放的季节变化趋势。但在降雨或者升温事件发生时，土壤CO2和N2O排放的模型模拟值与实际观测值在峰值大小和响应时间上存在差异。模型模拟表明未来本地区降雨量在±30%范围内变化时，林地土壤CO2和N2O排放量的变化幅度不超过30%；气温在±3℃范围内变化时，林地土壤CO2和N2O排放量的变化幅度不超过10%。(5) 土壤温度和土壤湿度是影响桤柏混交林土壤各分室呼吸速率的主要环境因素。土壤各分室呼吸温度和湿度敏感性指数大小顺序均为根呼吸>枯枝落叶层呼吸>矿质土壤呼吸，表明桤柏混交林根呼吸对土壤温度和湿度的敏感性要高于枯枝落叶层呼吸和矿质土壤呼吸。采用挖壕沟法和根系生物量回归法对比测定了林地根呼吸速率，两种方法测得的根呼吸比例变化范围分别为28.26%~69.09%、23.10%~57.14%，平均值分别为43.97%和38.31%，方差分析表明二者之间差异不显著(p>0.05)。(6) 研究表明在测定期间，桤柏混交林生态系统碳平衡为2.881 tC•hm-2•a-1，每年可固定大气中的CO2量为10.56 t•hm-2•a-1。桤柏混交林普遍由于立地条件较差、林分缺乏管理造成生产力较低，碳汇功能不明显。但从另外一个侧面也反映如果对林分进行更好的抚育与管理，将会更好的发挥其碳汇潜力。 |
| 英文摘要 | Global warming is one of the important environment issues. Natural events and human activities are believed to be contributing to an increase of average global temperatures. This is caused primarily by increases in “greenhouse” gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Global change has been concerned about worldwide because climate change characterized by global warming and atmospheric CO2 enrichment is changing the structure and function of terrestrial ecosystem, and in turn threatening the human existence and health. Therefore, global change mitigation is one of the most essential scientific issues in climate change researches. As an important source, sink, and pool in global carbon cycle, forest plays an important role in mitigating global change. Study on the influence of afforestation on terrestrial carbon sink has become one of the research hotspots in global change and forestry practice. The importance of afforestation on terrestrial carbon sink was affirmed by IPCC. Soil carbon sequestration by artificial forest has been considered as a truly win-win strategy, and the most promising choice to decrease the rate of enrichment of atmospheric concentration of carbon dioxide. Therefore, soil carbon sequestration potential of artificial forest is a key scientific issue of global change mitigation. China has the largest plantation area, with nearly one third of the global total, strengthening the objective research of afforestation and its terrestrial carbon sink, will have an important politic, scientific significance in China. The mixed plantations of alder (Aluns cremastogyne) and cypress (Cupressus funebris) (MPAC) were developed successfully on large scale in hilly areas of the central Sichuan Basin from 1970s to 1980s. Presently, this type of mixed plantations has become a primary protective forestry ecosystem in the upper reaches of the Yangtze River. Experiment site is located at Yanting Agro-ecological Station of Purple Soil, Chinese Academy of Science under Chinese Ecosystem Research Network (CERN). The mixed plantation soil greenhouse gas (CH4, N2O and CO2) fluxes were measured from January, 2005 to December, 2006. The mainly research were focused on the characteristics and influencing factors of soil greenhouse gases flux, forest biomass and primary productivity, ecosystem carbon pools and the carbon budget of soil and forest ecosystem. The results and conclusions were in the followings:(1) Soil greenhouse gases fluxes in the mixed plantation showed remarkably seasonal changes, which were higher in summer and autumn and lower in spring and winter. Forest soil was a source of CO2 and N2O emissions and a weak sink of CH4 flux. Annual fluxes of soil CO2, N2O and CH4 were 4892.8 kgC ha-1a-1, 0.98 kgN ha-1a-1 and 1.74 kgC ha-1a-1, respectively. Litter-cleared have significant effects on soil CO2 and N2O emissions, but has no impacts on CH4 absorption.(2) The temperature sensitivity of soil CO2 flux has an obviously seasonal variance. There was a significantly negative relationship between Q10 values with soil temperature and a positive relationship with soil moisture. The relationship equations were as follows: Q10=-0.0835T+3.4362(R2=0.67, n=12, p<0.01); Q10=0.1741W- 2.4718(R2=0.51, n=12, p<0.01). It indicated that in the range of the measured soil temperature and soil moisture, 1°C increase in soil temperature at 5cm depth will reduce the Q10 value by 0.0835, and 1% decrease of soil moisture will reduce the Q10 value by 0.1741, which will cause a significant reduction in soil respiration because of the nonlinear relationship of soil respiration with Q10.(3) Soil greenhouse gases sink and source has been affected by a long term drought. In drought period during June to August in 2006, the rates of soil greenhouse gases flux were all decreased to some extent compare with the corresponding period of 2005 year. And N2O flux was affected most significantly by drought.(4) The seasonally changes of forest soil CO2 and N2O fluxes can be fitted well by Forest-DNDC model. But there were some differences in observation values with simulation values in the case of a rainfall or temperature-increased events occurred. The modeling result showed that the changes of forest soil CO2 and N2O fluxes would be less than 30% in the range of ±30% rainfall changed, and less than 10% in the range of ±3℃ air temperature changed.(5) Soil temperature and soil moisture were primary impact factors of soil compartments respiration. The sequences of temperature and moisture sensitivity of soil compartments respiration were: root respiration > litter respiration > basal soil respiration. A trenching method and root biomass regression method were used to determine the contribution of root respiration to soil respiration, and there was no significantly difference between the results obtained by the two methods. The contributions of root respiration were higher in the growth seasons and lower in the non-growth seasons.(6) Forest soil carbon budget was 0.116 tC•hm-2•a-1. And ecosystem carbon budget was 2.881 tC•hm-2•a-1 during the measurement period. It indicated that this mixed forest ecosystem was a carbon sink for atmosphere CO2. The carbon sink efficiency of the mixed plantations of alder and cypress was lower because of poor forest quality and short of management. On the other hand, it also reflects that the forests is a huge potential carbon sink in the future if current mixed forests is fostered and managed well. Therefore, foster and management of current forests of alder and cyperess is very important for carbon sequestration. |
| 学科主题 | 生态学 ; 土壤学 |
| 语种 | 中文 |
| 公开日期 | 2010-10-21 |
| 分类号 | S71;S7 |
| 源URL | [http://ir.imde.ac.cn/handle/131551/2270]  |
| 专题 | 成都山地灾害与环境研究所_成都山地所知识仓储（2009年以前） 成都山地灾害与环境研究所_山地表生过程与生态调控重点实验室 |
| 推荐引用方式 GB/T 7714 | 王小国. 川中丘陵区桤柏混交林土壤温室气体排放与生态系统碳收支[D]. 成都. 中国科学院水利部成都山地灾害与环境研究所. 2007. |
入库方式： OAI收割
来源：成都山地灾害与环境研究所
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