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

陆地碳汇的大小是由总初级生产力（GPP）和生态系统呼吸（ER）的比值决定的，前者是指植物从大气中吸收二氧化碳的主要速率，后者是指生态系统中所有生物释放的二氧化碳。目前，陆地碳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，从而显著减缓了人为造成的全球变暖。不幸的是，GPP不能直接量化，而必须通过测量和模型的结合来估计。目前，这通常是通过将生态系统净二氧化碳交换划分为潜在的GPP和ER组件来完成的，这有许多公认的局限性。由此产生的GPP和ER估计值的不确定性极大地阻碍了旨在预测未来可能的气候和土地利用情景下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，羰基硫化物交换和太阳诱导荧光测量，减少当前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，但与二氧化碳相比，没有观察到羰基硫化物的排放，这使其成为GPP的代表。太阳诱导的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存在着一种关系，因为这两个过程都在争夺同样的能量。提议项目的假设是，由于这两种方法产生了关于GPP的互补信息——羰基硫化物的目标是漫射和太阳诱导的荧光（光合作用的能量供应成分）——它们的联合使用将允许减少二氧化碳通量测量得出的GPP的不确定性。迄今为止，这两种新方法是单独使用的，拟议的项目通过将它们联合使用，目的是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的两个野外活动中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，以及利用实验数据进行基于过程的模拟建模。

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.