绿洲盐碱湿地土壤碳平衡特征、源/汇功能及其影响机制

Soil salinization in arid regions affects the processes of carbon storage and emission in oasis wetlands, may even cause the transformation of source and sink functions. But so far the generations and influence mechanisms of CO2 and CH4 in saline-alkaline wetlands are still uncertain, and it is unclear whether the ionic stresses have significant impacts on carbon cycle and potential for reducing emissions in saline-alkaline wetlands. Therefore, the characteristics of carbon balance, the function of source/sink and its transformation mechanism have been become burning problems for researches on evaluation and prediction of carbon emissions of saline-alkaline wetlands in arid regions. This project will take oasis saline-alkaline wetland in arid region as research object and focus on the following three research parts: (1) the characteristics of soil carbon balance and distribution patterns of carbon source and sink in wetland will be studied in depth; (2) the contributions of soil organic or inorganic carbon from a variety of sources to soil carbon reserves will be accurately evaluated; (3) the coupling models of soil carbon accumulation and carbon emission will be established to predict the evolution tendency of soil carbon cycle and its functions of carbon source and sink in wetland under uncertain conditions such as salt and water levels. These research works can provide scientific basis for the estimation of carbon emission and reduction potential at saline-alkaline wetlands in arid regions.

干旱区土壤盐碱化影响着绿洲湿地碳储存与排放过程，甚至可能引起源/汇功能的转化，但目前盐碱湿地CO2、CH4气体的产生及影响机制仍不确定，且离子胁迫对盐碱湿地碳循环过程及减排潜力能否造成显著影响并不清楚。因此，湿地土壤碳平衡特征、源/汇功能及其转化机理是干旱区盐碱湿地含碳气体排放评估与预测亟待解决的重要科学问题。本项目以干旱区绿洲盐碱湿地为研究对象，深入探讨湿地土壤碳平衡特征和碳源/汇分布格局，准确评估不同来源的土壤有机碳和无机碳对土壤碳库的贡献，构建土壤碳储存与排放耦合模型，预测盐分和地下水等不确定条件下湿地土壤碳循环与源/汇功能的演变趋势，为干旱区盐碱湿地碳排放与减排潜力的预估提供科学依据。

绿洲湿地是干旱区重要的有机碳储库。然而，干旱区绿洲湿地CO2、CH4气体产生及离子胁迫对碳储量与减排潜力的影响机制仍不确定。因此，如何深入研究土壤碳循环过程、源/汇效应是干旱区绿洲盐碱湿地温室效应研究急需解决的关键问题。本项目以黑河中游绿洲湿地作为研究对象，通过长期野外定位试验、野外控制试验、同位素分析等研究方法，探讨干旱区绿洲盐碱湿地土壤碳平衡特征、碳源/汇功能及其影响机制。研究表明：(1)绿洲湿地年平均降水量为124.5±12.4 mm，ET为596.94~620.23 mm yr-1，地下水埋深为84.7±5.7~ 132.87±10.5 cm，土壤水分特征曲线分为0<pF≤1.86、1.86<pF≤2.52和pF>2.52三个吸力段，土壤总孔隙度、毛管孔隙度与非毛管孔隙度均存在显著差异。(2)不同类型湿地土壤有机质含量存在较大差异，且随土层深度的递增呈递增趋势，其均值介于1.90% ~ 2.35%。(3) 绿洲湿地年均土壤呼吸速率表现为：草地湿地(2.25~4.12μmol·(m2·s)–1)>柽柳湿地(1.10～3.65 μmol·(m2·s)–1)>沙枣湿地(0.26～1.53 μmol·(m2·s)–1)。(4)在河岸带距河0-4.0 km范围内，土壤有机碳、总碳、土壤碱解氮、总氮、速效磷、全磷含量且距河道不同距离梯度下差异显著。(5) 在绿洲湿地，总碳、总氮和总磷存储量均随土壤含盐量的增加而增加，说明盐渍化增加湿地土壤养分贮量。(6) 降水、河水和地下水中的铵态氮是湿地土壤植被的主要氮源，活性碳是主要碳源；植物腐殖质在湿地沉积物有机碳(占76.5%)、氮(占62%)来源端元占最大贡献率。(7) 在黑河中游，草地湿地、沙枣湿地和柽柳湿地 CH4和CO2排放年通量及季节通量存在显著差异性，主要受气温、土温及水位三者综合控制，其中CH4年年通量分布为 2.02、4.36和8.39 mg m-2 h-1，CO2年通量202.48、254.69和158.68mg m-2 h-1，碳收支均为正值(2.50±0.24、1.67±0.21和1.68±0.23 t hm-2 a-1)，故碳源/汇作用均为碳的强吸收汇。