Carbonyl sulfide as a proxy for gross primary productivity

Gross primary productivity (GPP) is the proximate driver of the contemporary land carbon sink, which helps slow down global warming. Unfortunately, GPP, at least on ecosystem-scale, cannot be measured directly and instead indirect approaches need to be used to approximate GPP. One of these are ecosystem-scale flux measurements of carbonyl sulfide (COS), which however require the a priori knowledge of the so-called leaf relative uptake rate (LRU), which is poorly constrained. The overarching objective of the proposed project is to advance the science of using COS as a proxy for GPP and thus to reduce the uncertainty of the resulting GPP estimates. The first objective to that end is to (i) experimentally quantify variability in LRU, (ii) analyze it based on our current theoretical understanding of leaf gas exchange using an eco-evolutionary optimality framework and (iii) devise an improved parsimonious parameterization of the leaf internal conductance to COS and LRU. The second major objective is to improve our understanding of leaf to canopy scaling of LRU in order to reduce uncertainty of GPP estimates resulting from the application of leaf-scale LRU parameterizations to ecosystem-scale flux measurements. The proposed 4-year project blends experimental measurements in the field on leaf, soil and ecosystem scale and leaf-scale laboratory measurements with leaf to ecosystem-scale modelling using a combination of eco-evolutionary optimization theory and multi-layer canopy model. The proposed project will advance the state-of-the-art by (i) attempting a universal and parsimonious parameterization of LRU based leaf-scale field and laboratory measurements and the application of a novel eco-evolutionary optimality theory, (ii) providing urgently needed data on the leaf internal conductance to COS and (iii) exploring leaf to ecosystem scaling effects of LRU using a combination leaf and ecosystem-scale measurements and multi-layer canopy modelling.