Background
The authors write that "the development of crops which are well suited to growth under future environmental conditions such as higher atmospheric CO2 concentrations is essential to meeting the challenge of ensuring food security in the face of the growing human population and changing climate," and they say that "a high-yielding indica rice variety (Oryza sativa L. cv. Takanari) has been recently identified as a potential candidate for such breeding, due to its high productivity in present CO2 concentrations."

What was done
"To test if it could further increase its productivity under elevated CO2," in the words of Chen et al., "Takanari was grown in the paddy field under season-long free-air CO2 enrichment (FACE, approximately 200 ppm above ambient CO2) and its leaf physiology was compared with the representative japonica variety 'Koshihidari'."

What was learned
The six Japanese scientists report that (1) "maximum ribulose-1,5-bisphosphate carboxylation and electron transport rates were higher for Takanari at the mid-grain filling stage in both years," that (2) "mesophyll conductance was higher in Takanari than in Koshihikari at the late grain-filling stage," that (3) "in contrast to Koshihikari, Takanari grown under FACE conditions showed no decrease in total leaf nitrogen on an area basis relative to ambient-grown plants," that (4) "Chlorophyll content was higher in Takanari than in Koshihikari at the same leaf nitrogen level," and, last of all, that (5) "Takanari showed consistently higher midday photosynthesis and stomatal conductance than Koshihikari under both ambient and FACE growth conditions."

What it means
In light of their several findings, Chen et al. conclude that "Takanari maintains its superiority over Koshihikari in regards to its leaf-level productivity when grown in elevated CO2," and, therefore, they suggest that Takanari "may be a valuable resource for rice breeding programs which seek to increase crop productivity under current and future CO2 concentrations."