Constraining terrestrial gross primary productivity by joint measurements of the carbonyl sulfide exchange and sun-induced fluorescence

陆地碳汇的大小取决于总初级生产力（GPP）与生态系统呼吸（ER）的比率，前者是植物从大气中吸收二氧化碳的主要速率，后者是生态系统中所有生物释放二氧化碳的速率。目前，陆地汇清除了人类活动排放到大气中的大约四分之一的二氧化碳，从而大大减缓了人为造成的全球变暖。不幸的是，GPP不能直接量化，而是必须通过测量和模型的组合来估计。目前，这通常是通过将净生态系统二氧化碳交换划分为基础的GPP和ER组件来完成的，这具有许多公认的局限性。由此产生的全球初级生产力和减排量估计数的不确定性大大妨碍了旨在根据未来可能的气候和土地使用情景预测陆地碳汇规模的努力。拟议项目的目标是通过联合应用两种新方法，硫化羰交换和太阳诱导荧光测量，减少目前全球初级生产力（并作为进一步的结果，ER）估计的不确定性。羰基硫相对于二氧化碳的优势在于它以类似的方式被叶子吸收，但与二氧化碳相反，没有观察到羰基硫的排放，使其成为GPP的替代物。太阳诱导荧光是指叶绿素分子吸收的光以较长的波长发射。荧光和光合作用之间的关系存在，因为这两个过程竞争相同的能量。所提出的项目的假设是，因为这两种方法产生关于GPP的互补信息-羰基硫靶向扩散和太阳诱导荧光，光合作用的能量供应部分-它们的联合使用将允许减少来自二氧化碳通量测量的GPP的不确定性。到目前为止，这两种新方法一直被单独使用-通过联合应用它们，拟议的项目旨在利用这两种方法的优势。为此，我们提出了一个综合的方法，包括联合测量的二氧化碳和硫化羰通量和太阳诱导的荧光在两个领域的运动，在两个对比鲜明的生态系统，一个中生态系统实验，和基于过程的模拟建模，利用实验数据。

The magnitude of the terrestrial carbon sink is determined by the ratio of gross primary productivity (GPP), that is the primary rate at which plants take up carbon dioxide from the atmosphere, to ecosystem respiration (ER), that is the release of carbon dioxide from all living beings in an ecosystem. At present, the terrestrial sink removes roughly one quarter of the carbon dioxide emitted into the atmosphere by human activities and thus significantly slows down anthropogenic global warming. Unfortunately, GPP cannot be directly quantified, but instead must be estimated through a combination of measurements and models. At present, this is typically done by partitioning the net ecosystem carbon dioxide exchange into the underlying GPP and ER components, which has a number of acknowledged limitations. The resulting uncertainty of GPP and ER estimates considerably hampers efforts aimed at projecting the magnitude of the terrestrial carbon sink to likely future climatic and land-use scenarios. The objective of the proposed project is to reduce the uncertainty of present-day GPP (and as a further consequence, ER) estimates by means of the joint application of two novel approaches, carbonyl sulfide exchange and sun-induced fluorescence measurements. The advantage of carbonyl sulfide over carbon dioxide is that it is taken up by leaves in a similar fashion, but in contrast to carbon dioxide no emission of carbonyl sulfide has been observed, making it a proxy for GPP. Sun-induced fluorescence refers to light absorbed by chlorophyll molecules that is emitted at a longer wave length. A relationship between fluorescence and photosynthesis exists because both processes compete for the same energy. The hypothesis underlying the proposed project is that because the two approaches yield complementary information about GPP – carbonyl sulfide targets the diffusive and sun-induced fluorescence the energy provisioning component of photosynthesis - their joint use will allow reducing the uncertainty of GPP derived from carbon dioxide flux measurements. So far, these two novel approaches have been used in isolation – by applying them jointly, the proposed project aims at capitalizing on the strengths of both approaches. To this end we propose a combined approach including joint measurements of carbon dioxide and carbonyl sulfide fluxes and sun-induced fluorescence during two field campaigns in two contrasting ecosystems, a mesocosm experiment, and process-based simulation modelling making use of the experimental data.