Warming and drying effects on tundra carbon balance

冻土碳(C)储量的变化被认为是陆地生态系统对大气CO2浓度最重要和最快速的反馈之一。如果永冻土C的可用性在更温暖和更干燥的气候中增加，正如对研究区域的预测那样，这些系统可能从碳汇转变为碳源，并对全球气候变化起到重要的正反馈作用。本研究的目的是确定温度和湿度如何影响高原冻土带生态系统的生态系统碳平衡。这项工作将在永久冻土碳实验加热研究项目中进行，该项目是2008年启动的一项深层土壤和生态系统变暖实验，于2011年扩大到包括地下水位操纵处理。该研究将验证一个假设，即升温和干燥会增加土壤碳的分解，减少植物对碳的吸收，导致生态系统碳的显著损失。这一假设将通过测量生态系统二氧化碳通量、呼吸源分配、植物生产力和生态系统营养动态来验证。这项工作将为气候变化对地下生产力和冬季呼吸的影响提供重要信息。这两个过程对冻土带C平衡有重要贡献，但它们对增温和干燥的响应尚未被量化。估算生态系统C响应的全部广度对于了解永久冻土生态系统的变化如何反馈给全球气候至关重要。这项拟议的研究将提供气候变化对冻土带C平衡影响的幅度和驱动因素的基本信息，并将把生物碳循环研究与物理科学中的永久冻土研究联系起来。此外，该项目将通过广泛使用放射性碳来检测呼吸二氧化碳的来源，弥合生态学研究和地球化学之间的差距。这项研究将在不连续的永久冻土带进行，在阿拉斯加的一个地区，在过去的几十年里，永久冻土带解冻和热岩溶一直在发生，永久冻土带的温度位于解冻点附近。该地区的生态系统变化可作为高纬度地区永久冻土退化所预期的未来变化的指标，使本研究与整个北极地区发生的变化高度相关。这项工作将对科学界和公众产生广泛的影响，因为它汇集了全球环境中的重要问题，并提高了对北方生态系统动态与全球气候系统之间联系的认识。拟议的项目将为一名博士后研究员和一组本科生提供培训机会，并将通过及时发表结果、在国家会议上发表报告和参与科学网络向科学界广泛传播。该项目将通过pi与教育中心、当地社区，特别是教师和外联协调员的持续合作，增进科学认识。

Changes in permafrost carbon (C) storage are expected to be one of the most important and rapid feedbacks from terrestrial ecosystems to atmospheric CO2 concentrations. If the availability of permafrost C increases in a warmer and drier climate, as predicted for the study region, these systems may switch from a C sink to source and act as a significant positive feedback to global climate change. The objective of this research is to determine how temperature and moisture affect ecosystem C balance in an upland tundra ecosystem. This work will be conducted within the Carbon in Permafrost Experimental Heating Research project, a deep-soil and ecosystem warming experiment initiated in 2008, which was expanded in 2011 to include a water table manipulation treatment. The research will test the hypothesis that warming and drying will increase decomposition of soil C and decrease plant C uptake, leading to significant ecosystem C losses. This hypothesis will be tested through measurements of ecosystem CO2 fluxes, respiration source partitioning, plant productivity, and ecosystem nutrient dynamics. This work will provide critical information about climate change effects on belowground productivity and winter respiration. These two processes contribute significantly to tundra C balance but their responses to warming and drying are not yet quantified. Estimating the full breadth of ecosystem C responses is critical for understanding how changes in permafrost ecosystems will feedback to global climate.This proposed research will provide essential information on both the magnitude and drivers of climate change impacts on tundra C balance, and will link biological carbon cycle research with permafrost research in the physical sciences. In addition, this project will bridge a gap between ecology research and geochemistry through the extensive use of radiocarbon to detect the sources of respired CO2. The research will be conducted in the discontinuous permafrost zone, in an area of Alaska where permafrost thaw and thermokarst have been occurring over the past several decades, and where permafrost temperatures are perched near the point of thaw. Ecosystem changes in this region serve as an indicator of future shifts that are expected with degrading permafrost at higher latitudes, making this research highly relevant to changes occurring across the Arctic as a whole.This work will have broad impacts on the scientific community and general public because it brings together important issues in the global environment and raises awareness of the connection between northern ecosystem dynamics and the global climate system. The proposed project will provide training opportunities for one postdoctoral researcher and a diverse group of undergraduate students, and will be widely disseminated to the scientific community through timely publication of results, presentations at national meetings and involvement with scientific networks. This project will enhance scientific understanding through continued work by the PIs with education centers, the local community and in particular, with teachers and outreach coordinators.