Canopy architecture, carbon gain and grain properties of native Australian rices: effects of elevated atmospheric carbon dioxide

Abstract

Wild relatives of Oryza will be increasingly used in commercial rice breeding programs. However, the effects of rising atmospheric CO2 concentration on photosynthesis, light interception, canopy architecture and grain properties of the wild species are unknown. Two accessions of the Australian wild rice, O. meridionalis (Cape York and Howard Springs), were grown in ambient (aCO2, 400 ppm) and elevated CO2 (eCO2, 700 ppm) with O. sativa cv. Doongara in glasshouses and compared for photosynthesis, light interception, biomass and carbon (C) gain. For grain quality and endosperm morphology characterisation, an accession of O. australiensis was also studied. Photosynthesis (Amax) was enhanced at eCO2 by 20–50% across all genotypes, doubling the number of tillers, leaves and biomass. Light interception (¯STAR) was lower in eCO2 than in aCO2 due to denser canopies and less dispersed leaves. Nevertheless, plant biomass and C gain were higher in eCO2 than aCO2, despite less efficient light interception. Wild rices had denser crowns and lower light capture than domesticated rice in both CO2 treatments. Grain physicochemical analysis showed that seed length, seed width and 1000-seed weight were higher in eCO2 than in aCO2. Protein content decreased at eCO2 by 23% in Doongara and 15% in Howard Springs. Peak and final flour viscosity increased in the wild rices at eCO2, but in Doongara, only peak viscosity increased. SEM images showed that aleurone cell length and width were higher in Howard Springs, but the area and length of starch granules were larger in Cape York in eCO2 than in aCO2. Responses of rice endosperm morphology to eCO2 were dependent on genotype. In conclusion, Australian and Asian rice species have qualitatively distinct traits and responses to eCO2, as seen in light interception, photosynthesis, canopy architecture and grain properties.