黄土高原植被自然恢复过程中土壤有机碳来源判定与周转特征

Researches on the turnover and origins of soil organic carbon are help to increase our understanding of the changing process of soil organic carbon under vegetation restorations, thus improve the accuracy in prediction of soil carbon sequestration potential for vegetation construction. Currently, the associated studies on soil carbon sequestration under vegetation restoration in the Loess Plateau are mainly focused on the soil organic carbon budgets, while the process of carbon turnover and origins received less attention, which restrict our understanding of the process and mechanism of soil carbon cycle. This study intends to take the natural vegetation recovery sequence at Ziwuling in the Loess Plateau as the research object. Based on the principles and methods of the stable carbon isotope tracer, the percentage and quantity of soil organic carbon derived from C3 and C4 vegetation under vegetation restoration would be calculated, and then the contribution of the new and old organic carbon on soil carbon storage would be evaluated. In addition, the rate and proportions of soil organic carbon mineralization would be measured after incubation in the laboratory, and the turnover time of whole soil organic carbon and derived from C3 and C4 vegetation would be determined by the kinetics equation of soil organic carbon decomposition basing on the results of stable carbon isotope analysis. Overall, the above research works would be enhance our knowledge on soil organic carbon turnover characteristics and variation process during vegetation restoration, and help to accurately assessing the long-term soil carbon sequestration effects for Grain for Green Project in the Loess Plateau.

对植被恢复过程中土壤有机碳来源和周转特征的研究能够增加对土壤有机碳固定过程的认识，有助于准确模拟和预测植被恢复后土壤有机碳库的演变趋势和固碳潜力。然而，当前黄土高原植被恢复的土壤固碳效应研究主要集中在土壤有机碳累积数量的变化，而对不同植被来源土壤有机碳变化动态及周转特征研究相对不足，限制了对土壤碳循环过程和机理的认识。本研究拟选择黄土高原子午岭植被自然恢复序列，基于稳定碳同位素示踪的原理与方法，研究该区植被恢复过程中土壤有机碳及其组分中C3和C4植物来源的比例和数量变化，定量评价新、老有机碳对土壤碳库的贡献；将稳定碳同位素分析结果与土壤有机碳矿化培养相结合，根据土壤有机碳分解动力学方程，计算土壤总有机碳和不同来源有机碳的矿化速率、可矿化比例、周转时间等，明确植被恢复过程中土壤有机碳的周转特征，为深入认识土壤有机碳固定过程和机理以及科学评估黄土高原退耕还林还草长期固碳效应提供理论依据。

为揭示植被自然恢复演替对土壤碳库动态变化与周转特征的影响与机制，本研究选取黄土高原子午岭林区不同恢复阶段植被演替序列为研究对象，通过研究不同植被恢复年限生态系统碳库及其组分的动态变化特征，探讨了该区植被和土壤碳库随植被恢复的变化规律，明确了土壤有机碳库和无机碳库随植被恢复的变化特征及其相互关系，评估新、老土壤有机碳对土壤碳库的相对贡献，明确了植被恢复过程不同来源土壤有机碳的周转特征。研究发现：（1）研究区生态系统碳库动态随植被恢复可分为两个阶段，在植被恢复的最初27年，生态系统碳库动态随土层深度变化波动增加，平均固碳速率为0.13 Mg ha-1 yr-1，在27年以后，生态系统碳库动态增速明显加快，其平均生态系统固碳速率为0.54 Mg ha-1 yr-1。（2）不同演替阶段植被群落土壤有机碳与无机碳之间存在极显著负相关关系，随着植被恢复演替，0-10 cm土壤有机碳含量显著增加；0-10 cm土壤无机碳表现出显著下降趋势。土壤无机碳含量和储量下降速率分别为0.052 g kg-1 yr-1和0.092 Mg ha-1 yr-1；下层土壤无机碳随植被恢复无显著变化趋势。（3）土壤新碳的增加速率在植被恢复初期（110.2 g m-2 yr-1）明显高于后期(28.2 g m-2 yr-1)，植被恢复初期新碳增加量约为后期增加量的3.9倍，土壤有机碳的分解速率在恢复初期（k=0.04）明显高于后期（k=0.005）。影响土壤有机碳固定速率的主要因素是土壤C：N，土壤新碳的增加量主要受到植物细根生物量的控制，土壤有机碳的分解速率主要有土壤粉粒含量决定。上述研究对于指导脆弱生态系统自然植被恢复过程中土壤碳库管理具有重要意义。