石羊河流域人工固沙林的固碳过程、速率和潜力研究

Afforestation has been regarded as an important measure to increase carbon sequestration. Sand-binding afforestation is the most effective and economical measures to control the desertified land, and must also impact on carbon stock of sandy ecosystem. However, the function of its carbon sequestraton was ignored in the past. In the Shiyang river basin in arid areas, comparing to the shifting sand dune, natural sandy shrub vegetation and native vegetation, carbon stocks of the artificial sand-binding forests with the different age, trees and management measures at the different sandy lands will be investigated to quantify and evaluate their carbon sequestration capacity, and to reveal the carbon sequestration process, rule and its driving mechanism of the artificial sand-binding forest. Spatial data at the different scale, tree and site condition will be obtained based on the satellite image and national forest inventory data to spatial pattern of carbon stocks of the artificial sand-binding forest in the Shiyang river basin. Using the carbon inventory tool of The Carbon Benefits Project (CBP) , the benefit and rate of carbon sequestration of the artificial sand-binding forest will be evaluated, and carbon sequestration potential of sand-binding afforestation under the different scenario will be forecasted. Base on above research results, possible pathways and regulation techniques to improve the carbon stock function of the artificial sand-binding forest will be put forward, which has important guidance significance for the tree selection and management of sand-binding afforestation in arid areas.

植树造林已公认为是增加碳汇的重要措施，而固沙造林作为治理沙化土地最有效的措施，也必然对沙地生态系统的碳储量产生影响，但是其固碳作用长期被忽视。以石羊河流域人工固沙林为研究对象，选择流动沙丘、天然灌丛与地带植被为对照，通过对不同沙化土地、不同树种、不同年代和不同管理措施人工固沙林碳储量的实地调查，量化与评价不同管理模式和不同树种人工固沙林的固碳能力，揭示典型人工固沙林碳储量的演变过程、规律与驱动机制；运用卫片解译与国家二类清查数据，获取不同区域和立地条件的碳储量空间数据，掌握石羊河流域人工固沙林生态系统碳储量时空格局；利用碳汇测量、监测和预测工具The Carbon Benefits Project (CBP)，评价石羊河流域人工固林的固碳效益和速率，预测石羊河流域固沙造林的固碳潜力，提出提高人工固沙林碳汇功能的可能途径和调控技术，为干旱地区固沙造林以及人工固沙林管理提供理论依据。

固沙造林作为干旱区沙化土地防治最有效的措施，必然会对沙地生态系统碳储量产生影响，但其固碳作用长期被忽视。本项目以石羊河流域人工固沙林为研究对象，选择流动沙丘与白刺灌丛为对照，研究了不同人工固沙林碳储量以及典型人工固沙林碳储量的演变过程和规律，评价了石羊河流域人工固林的固碳效益和速率，预测石羊河流域人工固林的固碳潜力，提出了石羊河流域人工固沙植被碳汇提升策略。结果表明：（1）人工梭梭林营造显著提高了沙地碳储量，其中地上地下植被及总碳储量随造林时间先增加后降低，1m深度土壤有机碳储量随造林时间逐渐增大；与稳定白刺灌丛相比，35年生人工梭梭林植被碳储量较高，但0-1 m土壤有机碳储量只占29.4%。（2）人工梭梭林土壤呼吸速率总体随种植年限增加而递增，结皮破坏会显著提高梭梭林的土壤呼吸速率。（3）CBP碳计量工具模拟发现，石羊河流域人工固沙林每公顷年固存CO2碳6.1吨，截止2020年每公顷大约可固碳244吨；未造林情景下，石羊河流域下游的荒漠区为碳源，40年（1980-2020年）累计释放CO2 2 187 190吨；造林后为碳汇，40年累计固存CO2 3 517 664吨。（4）人工梭梭林对风沙流活动的消减作用，显著促进了沙地表层土壤碳氮的积累。其中，地表风沙流引起的碳、氮输入速率分别为1.12 gC∙m-2∙a-1和0.15 gN∙m-2∙a-1，占到0-5 cm土壤有机碳、氮固定速率的21.5%和24.9%。；降尘引起的碳、氮输入速率分别为2.47 gC∙m-2∙a-1和0.29 gN∙m-2∙a-1，占到0-5 cm土壤有机碳、氮固定速率的45.7%和48.1%。（5）人工梭梭林营造能有效固定沙丘，林龄越长，风蚀引起的碳损失量越少，而且碳损失量随结皮破坏程度增大而增加。总体而言，石羊河流域人工固沙林营造消减了风沙流，显著提高了沙地植被和土壤碳储量，是干旱沙区增加碳汇的有效措施，但人工固沙林土壤碳库的恢复是一个漫长的过程，通过采取人工抚育修复措施可提高其固碳潜力。