Examining optimal photosynthetic profiles within vegetation canopies

Friday, December 13, 2019 - 16:45
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Earth system models (ESMs) use photosynthetic capacity, indexed by the maximum Rubisco carboxylation rate (Vcmax), to simulate carbon assimilation with an assumed dependence on leaf nitrogen determined from soil fertility. In contrast, new theory, based on biochemical coordination and co-optimization of carboxylation and water costs for photosynthesis, has found that optimal Vcmaxcan be predicted from climate. Building on this work, we test this new theory on a global, field-measured Vcmaxdataset of >100 within canopy light gradients from a variety of ecosystem types around the world. We first compare model-predicted Vcmaxto observed Vcmaxvalues to examine the interaction of biophysical constraints with light availability. Second, we examine the sensitivity of our Vcmaxpredictions to soil indices as proxies for N and water supply, temperature and other leaf traits strongly correlated to photosynthetic capacity such as leaf nitrogen per area (Na) and leaf mass per area (LMA). Finally, we review and contrast our findings in the context of other optimality theories based on N supply from the soil driving global photosynthetic capacity.

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