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NSFDEB-NERC: Addressing the plant growth C source-sink debate through observations, experiments, and modelling

NSFDEB-NERC：通过观察、实验和建模解决植物生长碳源库争论

基本信息

批准号：
NE/P011462/1
负责人：
Andrew Friend
金额：
$ 46.74万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FP011462%2F1
关键词：
NSFDEB NERC Addressing plant growth

项目摘要

Fossil fuel burning is causing atmospheric concentrations of the greenhouse gas CO2 to rise, the main driver of man-made climate change. However, the rate of CO2 rise is much slower than emissions suggest it should be. It appears that the land surface and oceans are together absorbing about 50% of annual CO2 emissions. Some field studies indicate that a large portion of the land surface uptake is due to increasing tree growth. However, the causes, locations, and future behaviour of this CO2 uptake remain highly uncertain. A plausible hypothesis is that this land uptake is occurring because higher levels of CO2 increase plant photosynthesis, meaning more carbon in plants. However, a number of scientists believe that tree growth is not commonly limited by the rate of photosynthesis itself, but is instead controlled by other factors such as rates of cell division, nutrients, or water supply. If this is true, it implies lower future uptake of CO2 on land than is currently assumed, and so greater rates of climate change. Improving our knowledge of plant responses to CO2 is clearly essential for policy makers to be able to forecast with confidence the impacts of any controls on CO2 emissions on future climate.When tree growth is limited by photosynthesis, we talk about 'carbon-limited' growth, whereas when it is limited by non-photosynthetic factors, it is 'sink-limited'. So, the extent to which trees are carbon-limited, and under which circumstances, is fundamental to understanding how they will respond to rising levels of CO2. Advocates of the importance of sink-limited growth point to findings of high concentrations of non-structural (storage) carbon observed in wood as evidence that carbon is abundant and not limiting, and thus growth is dominated by sinks, rather than by photosynthesis.In this project, we propose to significantly improve our understanding of this fundamental issue using a unique combination of observations, experiments, and modelling. We will focus on mature individuals of white pine, red maple, and red oak growing in Harvard Forest, Massachusetts. This is an international collaborative project, with the modelling and detailed wood development work led by the University of Cambridge and the field and laboratory carbon measurement work led by Harvard University. The Harvard team will measure non-structural carbon concentrations and photosynthetic rates, and take microcores from tree trunks for wood development measurements at high temporal and spatial resolutions. These cores will be analysed, under the management of Cambridge, in a Swiss laboratory that is expert in studying cellular development in wood. These observations will enable us to determine the relationships between carbon sources and sinks over time.In a highly innovative experiment, the Harvard team will also manipulate the supply of carbon to growing wood in our three experimental species at Harvard Forest by cooling the trees at particular points on their trunks. This cooling will be applied using cold collars, in which antifreeze will be circulated around the trunks of the experimental trees. Cooling will reduce the flow of sugars and we will conduct detailed measurements of the effects of changed carbon supply on wood development, and thus the extent to which growth is carbon limited.At Cambridge, we will use these various measurements to develop a computational model of tree growth, which will be incorporated into a global model of the terrestrial carbon cycle. This model will then be used to assess the consequences of sink-limited growth for historical and future global land carbon uptake. This work has the potential to revolutionise our understanding of the role of vegetation in the global carbon cycle, the impacts of environmental change on plants, our interpretations of past climates as recorded in tree growth rings, and, because of the effect plants have on atmospheric CO2, our predictions of future climate change.

化石燃料的燃烧导致大气中温室气体二氧化碳的浓度上升，这是人为气候变化的主要驱动力。然而，二氧化碳的上升速度远远低于排放量所显示的速度。陆地表面和海洋共同吸收了每年约50%的二氧化碳排放量。一些实地研究表明，很大一部分的土地表面吸收是由于增加树木的生长。然而，这种二氧化碳吸收的原因、位置和未来行为仍然高度不确定。一个合理的假设是，这种土地吸收的发生是因为更高水平的二氧化碳增加了植物的光合作用，这意味着植物中有更多的碳。然而，许多科学家认为，树木的生长通常不受光合作用本身的限制，而是受其他因素如细胞分裂，营养或供水的速度控制。如果这是真的，它意味着未来陆地上的二氧化碳吸收量比目前假设的要低，因此气候变化的速度更快。提高我们对植物对CO2反应的认识对于政策制定者能够有信心地预测任何控制CO2排放对未来气候的影响显然是至关重要的。当树木的生长受到光合作用的限制时，我们谈论的是“碳限制”的生长，而当它受到非光合作用因素的限制时，它是“汇限制”的。因此，树木受碳限制的程度以及在何种情况下，对于理解它们将如何应对二氧化碳水平的上升至关重要。库限制增长的重要性的倡导者点的高浓度的非结构性（存储）的碳在木材中观察到的证据表明，碳是丰富的，而不是限制，因此增长是由汇，而不是光合作用。在这个项目中，我们建议显着提高我们对这个基本问题的理解使用一个独特的组合的观察，实验和建模。我们将重点关注生长在马萨诸塞州的哈佛森林的白松、红枫和红橡树的成熟个体。这是一个国际合作项目，建模和详细的木材开发工作由剑桥大学领导，现场和实验室碳测量工作由哈佛大学领导。哈佛团队将测量非结构性碳浓度和光合速率，并从树干中提取微芯，以高时间和空间分辨率测量木材发育。在剑桥的管理下，将在瑞士一个专门研究木材细胞发育的实验室对这些核心进行分析。这些观测将使我们能够确定碳源和碳汇之间的关系随着时间的推移。在一个高度创新的实验中，哈佛团队还将通过冷却树干上特定点的树木，来操纵哈佛森林中我们三个实验物种生长木材的碳供应。这种冷却将使用冷圈，其中防冻剂将在实验树木的树干周围循环。冷却将减少糖的流动，我们将详细测量碳供应变化对木材生长的影响，从而测量生长受碳限制的程度。在剑桥，我们将使用这些不同的测量结果来开发树木生长的计算模型，该模型将被纳入陆地碳循环的全球模型。然后，该模型将用于评估汇限制增长对历史和未来全球陆地碳吸收的影响。这项工作有可能彻底改变我们对植被在全球碳循环中的作用的理解，环境变化对植物的影响，我们对树木年轮中记录的过去气候的解释，以及由于植物对大气CO2的影响，我们对未来气候变化的预测。