Warming and drying effects on tundra carbon balance

冻土碳储量的变化是陆地生态系统对大气CO2浓度最重要、最迅速的反馈之一。如果永久冻土碳的可用性增加，在一个温暖和干燥的气候，预测的研究区域，这些系统可能会从一个C汇切换到源，并作为一个显着的积极反馈，全球气候变化。本研究的目的是确定如何温度和水分影响生态系统C平衡在高地冻原生态系统。这项工作将在永久冻土中的碳实验加热研究项目内进行，该项目是2008年启动的一项深层土壤和生态系统变暖实验，2011年扩大到包括地下水位操纵处理。这项研究将验证这样一个假设，即变暖和干旱将增加土壤碳的分解，减少植物碳的吸收，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CO2通量、呼吸源分配、植物生产力和生态系统养分动态来检验。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重要信息。这两个过程有助于显着冻原碳平衡，但他们的反应，变暖和干燥尚未量化。估算生态系统碳响应的全宽度对于了解冻土生态系统的变化如何反馈到全球气候至关重要。这项拟议的研究将提供气候变化对冻原碳平衡影响的幅度和驱动因素的重要信息，并将生物碳循环研究与物理科学中的冻土研究联系起来。此外，该项目将通过广泛使用放射性碳来探测呼吸的二氧化碳的来源，从而弥合生态研究和地球化学之间的差距。这项研究将在阿拉斯加的一个地区进行，该地区在过去几十年中一直发生着永久冻土融化和热岩溶现象，永久冻土温度接近融化点。该地区的生态系统变化是未来变化的一个指标，预计随着高纬度永久冻土的退化，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，并提高了人们对北方生态系统动态与全球气候变化之间联系的认识。气候系统拟议的项目将为一名博士后研究人员和一批不同的本科生提供培训机会，并将通过及时发表成果、在国家会议上发言和参与科学网络，向科学界广泛传播。该项目将通过PI与教育中心，当地社区，特别是教师和外展协调员的持续工作来提高科学认识。

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.