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 (P < 0.05) negatively correlated with the quantum yield of PSII (?PSII), photochemical quenching (qP) and non-photochemical quenching (NPQ). Moreover, grain filling and grain weight under shading treatment were positively correlated with ?Sg, but negatively related to ?Sm in 2011. In contrast, a significantly (P < 0.01) negative association between grain weight and ?Lg was observed in 2010. It was found that lower values of ?Lg, ?Sm and ?Gm in rice indicated better light-harvesting and light-use capability and also higher grain filling and grain weight of rice.