Warming and drying effects on tundra carbon balance

永久冻土碳(C)储量的变化预计将是陆地生态系统对大气二氧化碳浓度最重要和最迅速的反馈之一。如果像对研究区域预测的那样，在更温暖和更干燥的气候下，永久冻土C的可获得性增加，这些系统可能会从C汇转变为源，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水分如何影响旱地冻土带生态系统的碳平衡。这项工作将在多年冻土中的碳实验供暖研究项目中进行，该项目是2008年启动的深层土壤和生态系统变暖实验，2011年扩大到包括地下水位操纵处理。这项研究将检验这一假设，即气候变暖和干旱将增加土壤C的分解，减少植物对C的吸收，从而导致显著的生态系统C损失。这一假设将通过对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养分动态的测量来验证。这项工作将提供有关气候变化对地下生产力和冬季呼吸影响的关键信息。这两个过程对冻土带C平衡的贡献很大，但它们对变暖和干燥的反应尚未量化。估计生态系统碳响应的全部范围对于理解冻土生态系统的变化将如何反馈给全球气候至关重要。这项拟议的研究将提供关于气候变化对冻土C平衡的影响的大小和驱动因素的基本信息，并将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，从而弥合生态学研究和地球化学之间的差距。这项研究将在阿拉斯加不连续的永久冻土带进行，该地区在过去几十年里一直在发生永久冻土融化和热岩溶，永久冻土温度接近融化点。这一地区的生态系统变化是未来随着高纬度永冻层退化而发生的变化的一个指标，使这项研究与整个北极发生的变化高度相关。这项工作将对科学界和普通公众产生广泛影响，因为它汇集了全球环境中的重要问题，并提高了人们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不同的本科生群体提供培训机会，并将通过及时发表成果、在国家会议上作陈述以及参与科学网络向科学界广泛传播。该项目将通过私人投资机构与教育中心、当地社区，特别是与教师和外联协调员的持续合作，增进科学了解。

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.