The relationships between carbon isotope discrimination and photosynthesis and rice yield under shading

The measurement of carbon isotope discrimination (∆) provides an integrated insight into the response of plants to environmental change. To investigate the potential use of ∆ for identifying shade tolerance in rice, five rice varieties were selected and artificially shaded (53% light reduction) during the grain-filling period in 2010 and 2011, in Sichuan, China. Shading treatment had a significant influence on the ∆ of rice organs, resulting in clear increases in the ∆ of stems plus sheaths (∆Sm), rice grains (∆Gm) and rice flour (∆Fm) at maturity, but a reduction in the ∆ of leaves (∆Lg) at the grain-filling stage. The relationships between ∆ and leaf photosynthetic and chlorophyll fluorescence characteristics and grain yield showed a close dependence on plant organs and light regimes. Under shading treatment, photosynthetic rate was negatively associated with ∆Gm and the ∆ of stems plus sheaths at the grain-filling stage (∆Sg), whereas ∆Sm was significantly (PPSII (PSII), photochemical quenching (qP) and non-photochemical quenching (NPQ). Moreover, grain filling and grain weight under shading treatment were positively correlated with ∆S g, but negatively related to ∆Sm in 2011. In contrast, a significantly (Passociation between grain weight and ∆Lg was observed in 2010. It was found that lower values of ∆L g, ∆Sm and ∆Gm in rice indicated better light-harvesting and light-use capability and also higher grain filling and grain weight of rice.