典型荒漠灌丛斑块土壤碳储量的精细估算研究

Soil carbon of desert ecosystem play an indispensable role in terrestrial ecosystem carbon cycle and stocks. Despite its importance and sensitivity to climate change, there exists large uncertainties in estimation of soil carbon storage. As the typical vegetation type of desert ecosystems, shrubs significantly increase the spatial heterogeneity of soil carbon, which is the biggest impact factors of uncertainties in the estimation of soil carbon storage. However, the related research on the individual scale is still uncommon. In this program, Reaumuria songarica (Pall.) Maxim. and Salsola passerina Bunge which are most widely distributed species of desert ecosystem in northern China were selected as our study object. Through field surveys, sampling and determination of physical and chemical properties, combined with traditional statistical and geostatistical methods, we research the spatial distribution characteristics of soil carbon content and accurate carbon storage on the individual scale, study the effect of shrub growth on soil organic carbon and inorganic carbon stocks and their stability. The biomass estimation models of shrubs has been introduced firstly to construct species-specific allometric models for estimating soil organic and inorganic carbon storage of shrub patch using easily measured variables, such as shrub crown and soil carbon density. This study contributes to comprehensively perceive the shrub function on carbon cycle of desert ecosystem and increase certainty of soil carbon storage estimation.

荒漠生态系统土壤碳储量是全球碳循环和气候变化的重要内容，但估算结果还存在极大的不确定性。灌丛作为荒漠生态系统的典型植被类型，显著增加了土壤碳的空间异质性，是土壤碳储量估算不确定性最重要的影响因子，然而在灌丛尺度上对土壤碳储量的相关研究还很少见。本项目以腾格里沙漠东南缘典型红砂和珍珠灌丛为研究对象，通过野外调查、取样及土壤理化性质测定，并结合传统统计学和地统计学方法，在个体尺度上精确研究灌丛斑块土壤碳的空间分布特征及储量大小；探明灌丛生长过程对土壤有机碳和无机碳储量及其稳定性的影响；首次引入灌丛生物量估算模型概念，将土壤碳储量的估算与灌丛生物量估算相结合，以灌丛形态特征和灌丛斑块间土壤碳密度为易测因子建立灌丛斑块土壤碳储量的估算模型，以期更全面深入认识荒漠生态系统碳储量。本研究有助于全面认知灌丛在荒漠生态系统碳循环中的作用，增加土壤碳储量估算的确定性。

荒漠生态系统土壤碳在全球碳循环中起着重要的作用，但是目前荒漠生态系统土壤碳储量估算结果不确定性极为明显，这已成为国家和区域尺度上碳储量评估以及国家政策制定的主要障碍。针对这一现状，在腾格里沙漠周边进行了大量的调查和系统研究，揭示了荒漠灌丛的生长显著改变了土壤有机碳、无机碳、全碳、可溶性有机碳、可溶性无机碳、可溶性碳、全氮、全磷、碱解氮、速效磷、pH、电导率、土壤粒径组成、土壤容重的水平和垂直空间分布特征；以灌丛形态特征、冠幅、冠幅面积、体积为自变量构建并筛选了红砂灌丛土壤有机碳、无机碳、全碳、全磷和全氮储量的最优估算模型，分别为SOC储量=4.5479×S0.9862、SIC储量=23.5035×S0.8100、TC储量=28.2046×S0.8359、TN储量=0.2604×S0.9159、TP储量=0.3382×S0.9428；构建了72个单一物种和24个混合物种的叶、新生枝、老龄枝、地上部、地下部和整株生物量的最优估算模型，最优模型主要是lnW（干物质生物量）=a+b×lnX（冠幅面积或灌丛体积）；对不同灌木群落的研究结果显示灌木群落是SOC含量的重要影响因素, 各土层SOC含量在10种群落间均存在显著差异，从土壤表层到深层, SOC含量主要表现为由高至低和先升高后降低两种特征，SOC含量与黏粉粒含量、全氮(N)、全磷(P)和电导率呈显著的正相关关系, 与砂粒含量呈显著的负相关关系；与天然荒漠草地相比退化荒漠草地碳损失较为严重，其灌木、草本生物量碳和土壤有机碳密度仅为天然荒漠生态系统的14.901%、45.549%和26.852%，退化荒漠草地具有较强的固碳潜力，在进行人工植被建设后，恢复荒漠草地灌木、草本生物量碳和0-100 cm土壤有机碳密度显著增加，分别为退化荒漠草地的2.463倍、5.305倍和2.392倍，总有机碳密度增加了1.152 kg·m-2。结合灌丛斑块土壤碳、氮、磷储量估算模型，灌木生物量估算模型以及不同群落和退化恢复植被类型，可以更全面的认知荒漠生态系统碳、氮、磷的在地球化学循环中的作用。