增温下多年冻土区高寒草地非生长季CO2排放与生态系统碳源汇对冻融循环的响应机制研究

Effects of climate warm on ecosystem sink/source depend on whether the plant C uptake could offset the increases of ecosystem respiration (ER), especially，the non-growing season CO2 emission may influence the annual C balance，which has become one of the key problem in the Arctic tundra ecosystem C cycle. However, there is few information about the warming effect on the relationship between non-growing season CO2 emission and annual C balance. Thus, we conducted a full year measurement of ER and its component and photosynthesis under warming treatment in different soil moisture conditions (alpine meadow and alpine swamp) in the permafrost region of Tibetan Plateau (TP). We focus on the response of ER to freeze-thaw cycle and the relationship to soil characteristics of active layer, plant phenology and environmental factors; and then, quantify the emissions of ER and its component and the contribution of non-growing season CO2 emission to annual C balance. The mechanism of warming effects on seasonal ER distribution were analyzed in alpine meadow and alpine swamp. This study will deepen our understanding of accurate assessment of ecosystem C source/sink in typical alpine grassland in the permafrost region of TP.

气候变暖背景下，多年冻土生态系统植被固碳量增加是否能够抵消生态系统呼吸碳排放将决定生态系统碳源汇，尤其是非生长季碳排放变化可能对年碳平衡起决定性作用，成为近来北极冻原碳循环研究的关键问题之一；然而，关于气候变暖下青藏高原多年冻土区非生长季碳排放与碳源汇关系的定量研究尚属空白。本项目选取高原腹地风火山地区不同土壤水分草地（高寒草甸和高寒沼泽草甸）为研究对象，通过模拟增温，对生态系统呼吸组分和光合作用进行全年动态监测，重点研究冻融交替过程生态系统呼吸动态变化特征及其与活动层土壤水热变化、植物物候和环境因子间关系；量化生态系统呼吸组分CO2排放，生态系统碳源汇及非生长季CO2贡献，解析增温下不同高寒草地生态系统呼吸季节分配格局及其影响机制。为准确评估气候变暖下青藏高原多年冻土区典型草地生态系统碳源汇提供科学依据。

气候变暖背景下，多年冻土生态系统植被固碳量增加是否能够抵消生态系统呼吸碳排放将决定生态系统碳源汇，尤其是非生长季碳排放变化可能对年碳平衡起决定性作用，成为近年来多年冻土区碳循环研究的关键问题之一。项目选取青藏高原多年冻土区高寒草甸和高寒沼泽草甸为研究对象，通过模拟增温，对生态系统呼吸、生态系统碳库、土壤理化性质和环境因子开展了监测，研究了冻融过程生态系统呼吸动态变化特征及其与活动层土壤水热、植物和环境因子间关系；量化呼吸组分、非生长季CO2贡献及生态系统碳源汇，进而明确模拟增温对高寒草地生态系统碳循环的影响。研究表明生态系统呼吸季节变化特征明显，沼泽草甸显著高于高寒草甸，非生长季占比达25%。高寒草甸和沼泽草甸土壤自养呼吸（Ra）/土壤呼吸（Rs）比率分别为37%和35%，无显著差异；Ra/Rs冻融过程较低，生长季达到峰值；呼吸组分主要受土壤温度和植物生物量驱动。短期增温（1年）下，两种草地类型土壤有机碳、微生物量碳含量呈下降趋势；中期增温（6年）下土壤碳库呈增加趋势，且高寒草甸显著增加。另一方面，增温显著增加两种草地类型生态系统呼吸CO2排放量，且高寒草甸增幅高于沼泽草甸，非生长季增幅高于生长季。中期增温促使高寒草甸植物总碳库增加量高于生态系统呼吸排放增加量，全年表现为碳汇；而沼泽草甸中幅度增温促使植物总碳库增加量高于生态系统呼吸排放增加量，表现为碳汇，而高幅度增温则相反，使生态系统为碳源。本研究明确了高原多年冻土区非生长季节CO2排放占比，不同增温幅度下生态系统呼吸的季节响应特征及生态系统碳库变化规律，研究结果有助于评估气候变暖下青藏高原多年冻土区典型草地生态系统碳循环变化。