An automated soil CO2 flux chamber system to study forest soil carbon budget

第68届联合国大会宣布2015年为国际土壤年（IYS2015；粮农组织，2015）。2015年土壤信息年的主要目标之一是倡导在各级（全球、区域和国家）快速增强土壤信息收集和监测的能力。土壤是粮食安全和基本生态系统功能的最重要因素之一。土壤储存了地球上最多的有机碳，在北温带和北方地区发现了最大的储量。土壤有机碳的动态仍然知之甚少，并且是预测由于人为活动而导致的未来气候变化情景的主要不确定性点。森林通过光合作用吸收大气中的二氧化碳（CO2），并最终通过凋落物和根系渗出物将其沉积到土壤有机碳库中，在全球碳循环中发挥着不可或缺的作用。森林还可以通过树木（主要是树根）的呼吸作用和分解凋落物的土壤微生物的作用来释放碳。根系呼吸和土壤动物分解有机物所产生的呼吸作用通常称为土壤全呼吸作用。如果森林处于平衡状态，则光合作用的吸收和呼吸作用的释放是平衡的。然而，这种平衡可能会受到土地利用的干扰，比如收获和气候变化。过去许多关于树木采伐对森林碳动态影响的研究都集中在地上碳过程和储量上。最近的一篇综述明确指出，迫切需要进行研究，分析采伐方法对森林土壤碳动态的长期影响，特别是在土壤有机碳储量最高的寒带和北温带森林（Clarke et al . 2015）。由于缺乏对采伐和气候变化下土壤有机碳动态的了解而产生的不确定性，限制了我们制定可靠的未来气候预测以及考虑全面碳动态的森林管理政策和指导方针的能力。在这个提案中，我们需要一个最先进的自动化土壤二氧化碳通量室系统，这将使我们能够在安大略省南部最近收获的松树人工林中对土壤二氧化碳（CO2）排放进行长期测量。我们将使用这些数据来量化和评估收获对林分碳动态的影响。这些数据还将用于验证加拿大地球系统模型中使用的陆地表面模型，即碳氮加拿大陆地表面方案（CN-CLASS）。本项目收集的数据将增进我们对土壤碳动态的了解，帮助改进气候预测，并向当地森林管理者通报收成对森林土壤碳动态的影响。

The 68th UN General Assembly declared year 2015 the International Year of Soils (IYS2015; FAO, 2015). One of the main objectives of IYS2015 is advocating for rapid capacity enhancement for soil information collection and monitoring at all levels (global, regional and national). Soils are one of the most important factors for food security and essential ecosystem functions. Soils store the largest amount of organic carbon on Earth, with the largest stocks found in northern temperate and boreal regions. The dynamics of soil organic carbon are still poorly understood and are a major point of uncertainty in predicting future climate change scenarios due to anthropogenic actions. Forests play an integral role in the global carbon cycle by absorbing atmospheric carbon dioxide (CO2) through photosynthesis and eventually depositing it into the soil organic carbon pools through litterfall and root exudates. Forests can also loose carbon, through respiration by trees, mainly roots, and by soil microorganisms that decompose the deposited litter. Root respiration and respiration due to decomposition of organic matter by soil fauna is often referred to as total soil respiration. If a forest is in a state of equilibrium, the uptake due to photosynthesis and release due to respiration are balanced. However, this balance can be disturbed by land-use, such as harvesting and climate change. Many past studies on the impacts of tree harvesting on forest carbon dynamics have focused on above-ground carbon processes and stocks. A recent review has clearly identified an urgent need for studies that analyze the long-term impacts of harvesting methods on forest soil carbon dynamics, especially in boreal and northern temperate forests, which have the highest soil organic carbon stocks (Clarke et al 2015). The uncertainty resulting from the lack of knowledge on soil organic carbon dynamics under harvesting and climate change is limiting our ability to develop robust future climate forecasts and also forest management policies and guidelines that account for full carbon dynamics. In this proposal, we are requesting a state-of-the-art AUTOMATED SOIL CO2 FLUX CHAMBER SYSTEM, which will enable us to make long-term measurements of soil carbon dioxide (CO2) emissions in a recently harvested pine plantation forest located in southern Ontario. We will use these data to quantify and assess the harvest impact on the stand's carbon dynamics. These data will also be used to validate the land surface model, the carbon-nitrogen Canadian Land Surface Scheme (CN-CLASS), used in Canadian Earth System Model. Data collected in this project will add to our understanding of soil carbon dynamics, help improve climate predictions, and inform local forest managers on the impacts of harvests on forest soil carbon dynamics.