Understanding environmental and physiological controls of the leaf COS:CO2 uptake relationship for better photosynthesis estimates
Abstract
Using carbonyl sulfide (COS) to estimate photosynthesis requires quantitative knowledge of the relationship between leaf COS and CO2 uptake. This relationship is routinely expressed in a simple metric — leaf relative uptake (LRU) ratio — defined as the concentration-normalized ratio of COS and CO2 uptake. Field and laboratory studies have shown that LRU is most sensitive to photosynthetically active radiation (PAR) and, to a lesser degree, relative humidity (RH). Patterns of this relationship also vary among species. Despite the large-scale and cross-species convergence of LRU to a constant ( 1.6), at the leaf and canopy scales, LRU variability presents a major challenge in field applications of COS-based photosynthesis estimates.
A process-oriented framework has been developed upon photosynthesis-stomatal conductance coupling to describe LRU as a function of PAR and RH. To understand how leaf physiological controls affect LRU patterns, we applied this LRU model to field measurements of leaf COS and CO2 fluxes in a semi-arid oak woodland (Stunt Ranch, CA, USA), a freshwater marsh (Irvine, CA, USA), and a boreal pine forest (Hyytiälä, Finland). Despite similar responses of LRU to PAR in these ecosystems, RH exerts a stronger control on LRU in the water-limited Californian ecosystems compared to the more humid boreal forest, due primarily to the differences in the Ball-Berry parameter of stomatal conductance. In the Hyytiälä boreal forest, it has been found that the LRU progression toward lower values in the growing season was not only driven by meteorological conditions but also associated with changes in stomatal conductance parameters. Of these species studied, the inferred ratio of COS internal conductance to photosynthetic capacity appears to fall into a narrow range, suggesting that COS uptake activity may be conservatively linked to photosynthetic capacity. This new approach to understanding LRU variability, which links directly to physiological parameters, has the potential to improve LRU predictability and would be particularly useful in upscaling leaf flux measurements in a heterogeneous canopy environment, thereby supporting accurate estimation of canopy photosynthesis using COS.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A43N3306S
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0428 Carbon cycling;
- BIOGEOSCIENCES