疏勒河上游多年冻土退化对土壤温室气体排放的影响研究

Being aimed at serious greenhouse effect problem caused by a large amount of soil greenhouse gas emissions with permafrost degradation on the Qinghai- Tibetan Plateau, conducting of systematic observation research is of important and urgent. The study is becoming a new international frontier and difficult field, and the degree of attention increases steadily. Three kinds of alpine permafrost (permafrost types are sub-stable, transitional and unstable permafrost, respectively) long-term observation sites in the upper reaches of Shule River Basin, on the northeast edge of the Qinghai-Tibetan Plateau, were selected as the research objects. Meteorological factors (e.g., air temperature and precipitation), soil environmental parameters in top of active layer soil, fluxes of the greenhouse gas (CO2, CH4 and N2O) emissions and other indicators (e.g., vegetation characteristics) were observed and investigated regularly. Based on those long-term observation data, patterns and differences of freeze-thaw cycle in the top of active layer soil in different permafrost and their influencing mechanism on greenhouse gas emissions were analyzed. Then, the influencing process and mechanism of permafrost degradation (such as stability decrease, active layer thickness increase) on greenhouse gas emissions were illustrated. In addition, long-term greenhouse gas emissions fluxes were stimulated and predicted by the Denitrification-Decomposition (DNDC) model. The goal of this project is to fill the gap of in-situ observations research in alpine permafrost region of the Qinghai-Tibetan Plateau. The results lay a foundation of long-term data accumulation, which could provide scientific basis and theoretical reference for understanding and assessing its role in carbon and nitrogen cycle of the Shule River Basin and its contribution and response to regional climate warming.

针对青藏高原多年冻土退化导致土壤温室气体大量排放所产生的温室效应问题，开展相关方面的系统观测研究是非常必要和紧迫的。该研究正在成为一项新的国际性前沿课题和难点领域，其重视度与日俱增。本项目拟选取高原东北缘疏勒河上游地区3种类型山地多年冻土（亚稳定型、过渡型和不稳定型）长期定位观测场为试验样地，定期监测气象要素、表层土壤环境和活动层厚度等各项指标参数及土壤温室气体（CO2、CH4和N2O）排放通量。从而，揭示各类型多年冻土活动层表层土壤冻融交替规律、异同性及对温室气体排放的影响机制，进而探讨多年冻土退化（稳定性下降、活动层厚度增加）对温室气体排放的影响过程和机理，同时利用土壤反硝化-分解模型模拟温室气体排放通量并预测其未来变化趋势。旨在填补高原山地多年冻土区原位观测研究的空白，为长期监测数据的积累奠定基础，也为认识和评估其在流域碳氮循环中的作用以及对区域气候变暖的贡献与响应提供科学依据。

本项目选取疏勒河上游3处试验样地（SLP2：亚稳定型多年冻土，高寒草甸；SLP4：不稳定型，高寒草原化草甸；SLP6：不稳定型，高寒草原）为研究对象，通过定期监测气象要素和土壤环境等及土壤CO2、CH4和N2O通量，揭示了活动层表层土壤冻融交替规律及其对土壤CO2、CH4和N2O排放的影响，并用多种方法模拟了温室气体排放通量。初步结果如下：（1）亚稳定型多年冻土表层2 cm土壤开始融化时间迟于不稳定型，而开始冻结时间早于不稳定型。随土壤深度增加，亚稳定型表层土壤的冻结日数逐渐增加，融化日数先增加后减少，冻融日数逐渐减少；而不稳定型冻结和融化日数先增后减，冻融日数逐渐减少。（2）三种温室气体在不同观测期均存在较大的变异。（3）利用整个观测期土壤温室气体地表通量与环境因子的回归模型估算年均排放总量，结果表明高寒草甸和高寒草原化草甸土壤N2O全年总排放通量分别为186.93和89.18 mg•m-2，CO2分别为1 479.24和962.20 g•m-2，CH4分别为-196.00和- 624.67 mg•m-2；非生长季土壤温室气体通量在年总通量中占有重要份额，不容忽视。（4）SLP4样地2 cm土壤温度、空气温度和总辐射、空气温度、2 cm土壤盐分分别是影响活动层表层2 cm土壤完全融化期、冻结过程期、完全冻结期、融化过程期土壤CO2通量的最重要因子。DNDC模型模拟土壤CO2年排放总量为1228 g•m−2，比不同冻融时期回归模型模拟结果低16%。.通过对18个样地的调查和观测，分析了多年冻土退化对地下碳密度及土壤CO2通量的影响。结果发现：随着多年冻土退化（稳定性下降），寒钙土表层0-10 cm的变化相比0-50 cm敏感；冷钙土表层0-10 cm土壤TC、SOC密度表现出先增加后减少；而0-50 cm SOC和BBC逐渐减少。高寒沼泽草甸和高寒草甸BBC、TC和SOC逐渐减少。高寒草原0-10 cm土壤TC和SOC逐渐减少。高寒草甸日均土壤CO2通量随着多年冻土退化先增加后减小，影响土壤日均通量的最重要因子是年均降水量。.本研究首次提出根据活动层表层土壤4个不同冻融时期CO2通量与环境因子的回归模型来估算CO2年排放总量，确定了DNDC模型应用于多年冻土区高寒草甸温室气体排放模拟的参数并获得较好模拟结果。研究成果有助于定量评估多年冻土退化对温室气体排放的影响。