Optimized leaf anatomy improves photosynthetic producing capacity of mid-season indica rice in the Yangtze River Basin during the genetic improvement

Abstract

The yield of mid-season indica rice in the Yangtze River Basin has greatly improved during genetic improvement, however, the underlying morphological-anatomical and physiological mechanisms are not clear. We assumed that the yield boost of mid-season indica rice during the genetic improvement was attributed to leaf photosynthesis improvement and leaf anatomy optimization. To verify this assumption, twelve mid-season indica rice cultivars (including hybrid combinations) from different periods in the Yangtze River Basin over the last 80 years were used in the present study to investigate the changes of rice biomass and grain yield during the genetic improvement and its eco-physiological photosynthetic basis through a two-year field and one-year pot trail. The results showed that rice biomass and grain yield, rice harvest index (HI), leaf net photosynthetic rate (A), stomatal conductance (gs), leaf nitrogen content per area (Narea), leaf mass per area (LMA), leaf thickness, the surface area of mesophyll cells exposed to intercellular airspace (IAS) per leaf area (Sm) and the surface area of chloroplasts exposed to IAS per leaf area (Sc) have remarkably increased, while the mesophyll conductance (gm), leaf area, leaf density, proportion of mesophyll cell periphery covered by chloroplasts (Sc/Sm) and the fraction of IAS (fias) showed no changes during the genetic improvement. Grain yield was positively correlated to both biomass and HI; biomass and yield were positively correlated to A at different growth stages; A was positively correlated to gs, gm, and Narea; A and gm were positively correlated with Sc. Biomass and grain yield were positively correlated with Narea, LMA, LT, Sm and Sc. We concluded that leaf senescence slowing, leaf thickening, enlargement of the surface area of mesophyll cells and chloroplasts exposed to IAS per leaf area have contributed to the biomass and yield boost during the genetic improvement in mid-season indica rice in the Yangtze River Basin by coordinately improving the photosynthetic capacity and photosynthetic functional period.