Collaborative Research: Environmental changes alter the carbon cycle of High Arctic ecosystems: shifts in the ages and sources of CO2 and DOC

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。北极正在经历结构和功能的变化，这些变化似乎是气候变化的结果，包括植被分布的变化，从生态系统向大气的CO2和CH4外排增加，以及溶解有机碳（DOC）从陆地向海洋输出的加速。在格陵兰岛西北部进行的研究提供了四条证据，证明气候变化正在以我们尚不完全了解的方式影响北极高纬度C周期。首先，极地半沙漠的土壤有机碳库占北极陆地表面的1 × 106平方公里，可能至少比以前的估计大6倍，并且在活动层中存在古老（30 ky BP）和年轻的土壤碳库。第二，二氧化碳生态系统交换测量结果一致显示，在生长季节，碳的净损失；然而，在温暖和潮湿的条件下，这些碳的损失在前一个冬天雪深适度增加的情况下被逆转。研究发现，当夏季升温1.3°C和2.4°C时，原位生态系统呼吸分别增加了25%和35%，而当较高升温水平与灌溉相结合时，原位生态系统呼吸增加了50%。第三，土壤CO2外排测量表明，古土壤C在植被凋落之前就被微生物降解了。预计损失将持续到整个生长季节，但被盛夏期间植物呼吸速率高（最近确定的C）所掩盖。④河流DOC的年际和时间格局不能简单地用夏季气候条件的差异来解释。阐明土壤溶液和河流中CO2和CH4交换量和DOC输出量随土壤呼吸CO2和DOC年龄的变化，确定不同土壤C库微生物降解对温度和湿度的敏感性，将改变我们对北极环境变化、生态系统功能和C循环的认识。本研究将解决这些问题：1。土壤呼吸CO2和DOC的年龄（最近固定的vs较老的）在一年中如何变化？这在多大程度上受到温度和降水年际变化的影响？它如何与CO2和CH4通量的模式相对应？2. 温度（+2和+ 4℃）和水输入（夏雨和冬雪）的长期实验增加在多大程度上改变了碳通量（CO2、CH4和DOC）的年龄、幅度和模式？3. 与较老的土壤C库相比，年轻土壤的微生物降解程度是否存在差异？降解率对气候变化的敏感程度有多高？

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The Arctic is undergoing structural and functional changes that appear to be the result of climate change, including shifts in vegetation distribution, increases in CO2 and CH4 efflux from ecosystems to the atmosphere, and the acceleration of dissolved organic carbon (DOC) export from land to oceans. Research in NW Greenland has produced four lines of evidence that climate change is affecting the High Arctic C cycle in ways we do not fully understand. First, soil organic C pools in polar semi-deserts, which occupy 1 x 106 km2 of the Arctic land surface, may be at least 6× greater than previous estimates, and ancient (30 ky BP) and young soil C pools are present in the active layer. Second, CO2 ecosystem exchange measurements have consistently shown net C losses during the growing season; these C losses are, however, reversed under warmer and wetter conditions and with modest snow depth increases during the previous winter. In situ ecosystem respiration has been found to increase by 25 and 35% with experimental summer warming of 1.3 and 2.4°C, respectively, but by 50% when the higher level of warming was combined with irrigation. Third, soil CO2 efflux measurements indicate that ancient soil C is being degraded by microbes before vegetation leaf-out. Losses are expected to continue throughout the growing season, but masked by high rates of plant respiration (recently-fixed C) during the mid-summer. Forth, interannual and temporal patterns of riverine DOC are not explained by simple differences in summer weather conditions. Articulating the magnitudes of CO2 and CH4 exchange and DOC export along with the ages of soil respired CO2 and DOC in soil solution and rivers, and determining the sensitivity of microbial degradation of different soil C pools to temperature and moisture will transform our understanding of environmental change, ecosystem function and C cycling in the Arctic. This study will address these questions: 1. How does the age (recently-fixed vs. older) of soil respired CO2 and DOC change over the course of a year, to what extent is this influenced by inter-annual variability in temperature and precipitation, and how does it correspond with the patterns of CO2 and CH4 fluxes? 2. To what extent do long-term experimental increases in temperature (+2 and + 4oC), and in water inputs (summer rain and winter snow) alter the ages, magnitudes, and patterns of C fluxes (CO2, CH4, and DOC)? 3. Are there differences in the extent of microbial degradation of young as opposed to older soil C pools and how sensitive are the degradation rates to changes in climate?