Collaborative Research: Controls on the Isotopic Composition of Fixed CO2 and Ecosystem-Respired CO2 in Southeastern Pine Forests

自从科学家将人类产生的二氧化碳与全球变暖联系起来以来，他们一直试图量化人类对气候的影响有多大。人类产生的一半二氧化碳——主要来自化石燃料的燃烧——仍留在大气中。另外“缺失的一半”要么被海洋吸收，要么在光合作用过程中被陆生植物吸收。要想了解人类活动如何影响全球气候和全球碳循环，了解碳排放的去向是至关重要的一环。追踪二氧化碳目的地的一个有用的标记是空气中二氧化碳中13C与12C的比值。陆地植物优先吸收12C，使空气富含13C。海洋在吸收二氧化碳时是一视同仁的。因此，通过测量13C和12C的比例，科学家可以判断二氧化碳是进入了陆地植物还是进入了海洋。但是陆地植物吸收13C到12C的量是不同的，所以预测人类产生的二氧化碳在哪里聚集的模型可能会有很大的误差。为了限制误差，并更好地估计二氧化碳的去向，一项新的研究将对北美最大的碳汇之一——南部松林进行调查。该研究将着眼于气候变化如何影响植物在呼吸过程中吸收和释放的二氧化碳的13C/12C比率。这一结果可能会对陆地植物作为人类产生的二氧化碳的“汇”的重要性进行重要的重新计算。这项研究将着眼于叶蜡和呼吸二氧化碳中的碳同位素组成。这将用于改进对陆地碳汇分布和规模的估计，这是进一步了解陆地植物作为人类产生的二氧化碳吸收者的重要性的一步。

Ever since scientists linked human production of carbon dioxide with global warming, they have sought to quantify how much impact humans have had on climate. Half the CO2 produced by humans-mainly from the burning of fossil fuels-remains in the atmosphere. The other "missing half" is either adsorbed by the oceans or taken up by terrestrial plants during photosynthesis. Knowing how much goes where is a crucial link in understanding how human activity affects global climate and the global carbon cycle. A useful marker to trace the destination of CO2 is the ratio of 13C to 12C in CO2 in the air. Land plants preferentially take up 12C, enriching the air in 13C. The oceans don't discriminate when they take up CO2. So by measuring the ratio of 13C to 12C, scientists can tell whether the CO2 is going into land plants or into the ocean. But there is variation in how much 13C to 12C land plants take up, so the models that predict where human-produced CO2 winds up can have significant error. To limit the error, and develop better estimates of the fate of CO2, a new study will be conducted to examine southern pine forests, one of the largest carbon sinks in North America. The study will look at how climate variability affects the 13C/12C ratio of the CO2 that plants absorb and release during their respiration. The result may yield a significant recalculation of how important land plants are as a "sink" for human-produced CO2.The study will look at carbon isotope composition in leaf waxes and respired CO2. This will be used to improve estimates of the distribution and magnitude of the terrestrial carbon sink, a step in further understanding the importance of land plants as absorbers of CO2 produced by humans.