Leaf canopy architecture determines light interception and carbon gain in wild and domesticated Oryza species

Oryza sativa has many wild relatives that exhibit a wide range of canopy architectures. Two fast-growing ecotypes of an Australian wild rice (O. meridionalis) were compared with cultivated O. sativa to analyze the efficiency of light interception in mature vegetative canopies and how well light capture predicts biomass production. Canopies of individual plants were digitized and analyzed with YplantQMC. Plants were also grown at 700 ppm CO2 as a means of increasing the canopy density and assessing the relative impact of rising CO2 levels on photosynthesis, light interception and biomass. Simulations of light interception for these morphologically diverse canopies were combined with photosynthetic light response curves to estimate theoretical carbon gain. Both O. meridionalis genotypes had more tillers and leaves, and denser canopies, than O. sativa but one ('Howard Springs') intercepted more light than the other two genotypes, resulting in the highest simulated carbon gains. Photosynthesis per unit leaf area (Amax) was enhanced by 20-50% in 700 ppm CO2 in all genotypes but the proportion of total leaf area intercepting light decreased as a result of denser leaf canopies in these plants. Estimated total shoot carbon gain increased strongly at elevated CO2 despite these denser canopies and increased self-shading, reaching a peak in 'Howard Springs' at 700 ppm CO2. Thus, while high crown density and low leaf dispersion reduced the efficiency of light interception by the canopy, elevated CO2 still enhanced growth through consistently higher assimilation rates. Simulations showed that during the Summer Solstice, carbon gain was predicted to be greater than at the Equinox through superior light capture, particularly in 'Howard Springs'. However, the relationship between light interception and carbon gain was broadly maintained, regardless of genotype, CO2 concentration and season.