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Summary Photosynthetic capacity per unit irradiance is greater, and the marginal carbon revenue of water (∂A/∂E) is smaller, in shaded leaves than sunlit leaves, apparently contradicting optimization theory. I tested the hypothesis that these patterns arise from optimal carbon partitioning subject to biophysical constraints on leaf water potential.In a whole plant model with two canopy modules, I adjusted carbon partitioning, nitrogen partitioning and leaf water potential to maximize carbon profit or canopy photosynthesis, and recorded how gas exchange parameters compared between shaded and sunlit modules in the optimum.The model predicted that photosynthetic capacity per unit irradiance should be larger, and ∂A/∂Esmaller, in shaded modules compared to sunlit modules. This was attributable partly to radiation‐driven differences in evaporative demand, and partly to differences in hydraulic conductance arising from the need to balance marginal returns on stem carbon investment between modules. The model verified, however, that invariance in the marginal carbon revenue of N (∂A/∂N) is in fact optimal.The Cowan–Farquhar optimality solution (invariance of ∂A/∂E) does not apply to spatial variation within a canopy. The resulting variation in carbon–water economy explains differences in capacity per unit irradiance, reconciling optimization theory with observations.
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Wide variation in the suboptimal distribution of photosynthetic capacity in relation to light across genotypes of wheat
Abstract Suboptimal distribution of photosynthetic capacity in relation to light among leaves reduces potential whole-canopy photosynthesis. We quantified the degree of suboptimality in 160 genotypes of wheat by directly measuring photosynthetic capacity and daily irradiance in flag and penultimate leaves. Capacity per unit daily irradiance was systematically lower in flag than penultimate leaves in most genotypes, but the ratio (γ) of capacity per unit irradiance between flag and penultimate leaves varied widely across genotypes, from less than 0.5 to over 1.2. Variation in γ was most strongly associated with differences in photosynthetic capacity in penultimate leaves, rather than with flag leaf photosynthesis or canopy light penetration. Preliminary genome-wide association analysis identified nine strong marker-trait associations with this trait, which should be validated in future work in other environments and/or materials. Our modelling suggests canopy photosynthesis could be increased by up to 5 % under sunny conditions by harnessing this variation through selective breeding for increased γ.
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- Award ID(s):
- 1951244
- PAR ID:
- 10230943
- Editor(s):
- Johnson, Daniel
- Date Published:
- Journal Name:
- AoB PLANTS
- Volume:
- 12
- Issue:
- 5
- ISSN:
- 2041-2851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/aobpla/plaa039
