High mesophyll conductance in the high-yielding rice cultivar Takanari quantified with the combined gas exchange and chlorophyll fluorescence measurements under free-air CO2 enrichment

摘要

An effective strategy for increasing crop production is increasing the rate of photosynthesis. In this study, we conducted gas exchange and chlorophyll fluorescence measurements for a high-yielding rice cultivar, Takanari, to identify the leaf physiological properties that contribute to high capacity for photosynthesis of the uppermost leaves before (panicle initiation stage) and after heading (grain-filling stage) in the Tsukuba free-air CO_(2) enrichment (FACE) facility. The higher photosynthesis rate of Takanari compared with that of the commonly cultivated cultivar, Koshihikari, was mainly attributed to the greater stomatal conductance for CO_(2) (g_(sc) ) at the panicle initiation stage and to the greater mesophyll conductance (g_(m) ) at the grain-filling stage in both current and elevated atmospheric CO_(2) concentrations [CO_(2)]. Takanari had a higher level of leaf nitrogen content (N_(l) ) compared with Koshihikari at the grain-filling stage, which led to greater g_(m) and maximum carboxylation rate (V_(c,) _(max)), but N_(l) alone did not explain the variations of g_(m) within the variety. A clear correlation was found between V_(c,) _(max) and N_(l) . Calculating V_(c,) _(max) taking g_(m) into consideration removed the artifact of V_(c,) _(max)_(25) in relation to N_(l) that was observed when g_(m) was assumed to be infinite. Our results emphasize the need to separate the roles of V_(c,) _(max) and g_(m) to accurately understand the ecophysiological processes that control leaf photosynthesis in Takanari.