Rapid responses of mesophyll conductance to changes of CO2 concentration, temperature and irradiance are affected by N supplements in rice

Photosynthesis in C-3 plants is significantly limited by mesophyll conductance (g(m)), which can vary with leaf anatomical traits and nitrogen (N) supplements. Several studies have investigated the response of g(m) to N supplements; however, none examined the implications of N supplements on the response of g(m) to rapid environmental changes. Here we investigated the effect of N supplement on g(m) and the response of g(m) to change of CO2, temperature and irradiance in rice. High N supplement (HN) increased mesophyll cell wall surface area and chloroplast surface area exposed to intercellular airspace per leaf area, and reduced cell wall thickness. These changes resulted in increased g(m). The g(m) of leaves with HN was more sensitive to changes in CO2 concentration, temperature and irradiance. The difference in leaf structural features between low N supplement and HN indicates that a rapid change in g(m) is related to the regulation of diffusion through biological membranes rather than leaf structural features. These results will contribute to an understanding of the determinants of g(m) response to rapid changes in environmental factors.