基于活性系数的碳库稳定性灌淤时间序列演变机制研究

To improve the stability of soil carbon pool is essential to increase soil organic carbon sequestration. Irrigation is an important way to ensure agriculture production in arid and sub-arid areas. It also played a more prominent role in increasing soil carbon sequestration. However, there are still some urgent questions need to be solved such as: 1) only attention has paid to the change in total soil organic carbon, not for the mechanism research of carbon components composition and stability of soil organic carbon in irrigated regions; 2) no quantitative evaluation has made on the potential capacity and stability of soil carbon by using a reasonable index. Ningxia Irrigation Zone will be selected as a case study to test the long-term effect of irrigation with Yellow River water on the evolution of soil carbon fraction composition and stability in China. Light and heavy fraction organic carbon of samples will be grouped by density grouping method. By comparing the content of light and heavy fraction organic carbon in this study with those sampled in 2009, the characteristic of soil carbon component composition and activity coefficient changed under two time chronosequences of irrigation with sediment laden water can be revealed, and the stability and effect of irrigation on soil carbon pool will be evaluated, and the potential of carbon sequestration will be predicted according to the change trend of activity coefficient under time chronosequences. In this study, both empirical and theoretical research were combined to reveal the evolvement mechanism of soil carbon composition and stability affected by long-term irrigation with sediment laden Yellow River water, and identify the dominate droving factors of carbon component and stability changed in Ningxia Irrigation Zone. Activity coefficient will be verified as a reasonable index to quantitatively evaluate the stability of soil carbon pool, and provide reliable theoretical and scientific basis in further study.

灌溉是干旱、半干旱地区保障农业生产的重要措施，对增加土壤固碳和碳库稳定性作用突出。以往的研究侧重分析灌溉对土壤总有机碳及组分含量变化的影响，未定量化评价碳库稳定性、分析其演变机制。因此，本研究拟选取时间序列明显的宁夏引黄灌区为研究对象，进行实地调查与采样，计算土壤碳库活性系数（轻组与重组有机碳含量之比），以2009年采样数据为基础，对比研究两个灌淤时间序列下土壤有机碳库组分构成和活性系数变化特征的异同；借助活性系数定量化评价土壤碳库稳定性及固碳潜力，预测其变化趋势，明确碳库活性系数在定量化评价土壤碳库稳定性时间序列演变中的可行性；运用地统计学方法研究有机碳组分含量、变化量与土壤属性和环境因子间的相互关系，揭示驱动土壤碳库稳定性演变的主导因素和作用机制。尝试运用碳库活性系数评价其稳定性并揭示引黄灌溉对土壤碳库稳定性演变的影响，为定量化评价区域碳库稳定性和采取合理措施增加土壤固碳提供科学依据。

通过研究引黄灌土壤有机碳组分的时间序列变化特征，初步揭示高含沙黄河水灌溉在提升土壤碳库稳定性、降低大气温室气体浓度中的特殊作用。结果表明，经引黄灌溉耕作后土壤轻组、重组和总有机碳含量分别由对照的23.43、3.94和4.19 g/kg增加到30.31、6.60和7.21 g/kg，轻组、重组和总有机碳含量平均分别增加了22.25%、2.66和3.02 g/kg。引黄灌溉不仅有利于增加土壤有机碳含量，更有利增加稳定性碳组分，提高土壤碳库的稳定性，重组有机碳与总有机碳存在显著相关关系(P＜0.001)。2015年，未受灌溉耕作影响的自然土壤表层（0-20 cm）及亚表层（20-30 cm）碳库活系数分别为114.28和155.84，引黄灌溉后表层及亚表层土壤碳库活性系数分别为55.95和67.32，表层土壤碳库活性系数小于亚表层，均随土壤总有机碳含量的增加呈幂函数递减趋势。宁夏灌区土壤粉粒和粘粒含量分别由31.35%和9.8%增加到48.55%和20.51%，砂粒含量由59.17%下降至30.95%（P<0.05）。土壤总有机质、重组和轻组有机质含量与粉+粘含量之间的相关系数分别为0.717、0.74和0.357，土壤细化有利于增加有机质。在宁夏引黄灌区，自然土壤大、中、小和<0.053mm土壤团聚体所占比例分别为5.42, 18.9, 48.8 和 26.8%，灌溉耕作土壤中分别为 9.51, 28.9, 38.69 and 22.9%，大团聚体和中间团聚体质量分数上升，微团聚体和粉＋黏团聚体有机碳质量分数下降，团聚体分布趋势为微团聚体＞粉＋黏团聚体＞中间团聚体＞大团聚体，小粒级团聚体所占比例多，但稳定性差，团聚体有机碳含量大小顺序为，粉＋黏团聚体＞大团聚体＞中间团聚体＞微团聚体，团聚体有机碳组成变化与团聚体组成变化规律一致，且呈随灌溉耕作时间延长而增加的趋势。除<0.053mm团聚体外，其他粒级的团聚体与粉粒+粘粒之间有明显相关性。砂粒与团聚体有机碳之间呈负指数关系，粉粒、粘粒和团聚体有机碳之间呈正相关关系。引黄灌淤耕作有利于增加稳定性有机碳组分和土壤团聚体的形成，具有良好的固碳减排效应。