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

陆地碳汇的大小由总初级生产力(GPP)和生态系统呼吸(ER)的比率决定，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的二氧化碳。目前，陆地汇清除了大约四分之一的人类活动排放到大气中的二氧化碳，从而显著减缓了人为的全球变暖。不幸的是，GPP不能直接量化，而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本的GPP和ER组成部分来完成的，这有一些公认的局限性。由此产生的GPP和ER估计的不确定性在很大程度上阻碍了旨在预测未来可能出现的气候和土地利用情景的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的方法--羰基硫化物交换和太阳诱导荧光测量--来减少目前GPP(以及进一步的结果，ER)估计的不确定性。与二氧化碳相比，羰基硫化物的优势在于，它以类似的方式被树叶吸收，但与二氧化碳相反，没有观察到羰基硫化物的排放，使其成为GPP的替代品。太阳诱导的荧光是指被叶绿素分子吸收的波长较长的光。荧光和光合作用之间存在关系，因为这两个过程都竞争相同的能量。拟议项目的基本假设是，由于这两种方法产生关于GPP的互补信息--以扩散和太阳诱导的荧光为目标，光合作用的能量供应部分--它们的联合使用将允许减少从二氧化碳通量测量得出的GPP的不确定性。到目前为止，这两种新的方法是单独使用的--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，我们提出了一种综合方法，包括在两个不同生态系统中的两个野外活动期间联合测量二氧化碳和羰基硫化物通量和太阳诱导荧光，一个中观实验，以及利用实验数据建立基于过程的模拟模型。

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.