Photosynthetic parameters and leaf carbon isotope composition (δ13C) in contrasting rice genotypes in relation to supplemental nitrogen (N) application and water management during the grain-filling period were compared. The changes in stomatal conductance (gs) and ratio of intercellular to ambient CO2 mole fraction (Ci/Ca) depended on the leaf nitrogen concentration (leaf N) in both ‘Hinohikari’ (temperate japonica genotype) and ‘IR36’ (indica genotype). In ‘Hinohikari’, δ13C reflects photosynthetic gas exchange during the grain-filling period, which is indicated by the significant response of δ13C to leaf N. In contrast, in ‘IR36’ δ13C did not depend on leaf N. This varietal difference in δ13C to leaf N can be attributed to a difference in the timing of leaf senescence. In ‘IR36’, leaf N and photosynthetic parameters decreased more rapidly, indicating earlier senescence and a shorter grain-filling period in comparison with ‘Hinohikari’. The significant increase in shoot dry mass in ‘Hinohikari’ resulting from supplemental N application, compared with nonsignificant effect observed in ‘IR36’, suggests that the timing of senescence in relation to the grainfilling period has a preponderant influence on productivity., S. Shimoda., and Obsahuje bibliografii
Tropospheric ozone (O3) decreases photosynthesis, growth, and yield of crop plants, while elevated carbon dioxide (CO2) has the opposite effect. The net photosynthetic rate (PN), dark respiration rate (RD), and ascorbic acid content of rice leaves were examined under combinations of O3 (0, 0.1, or 0.3 cm3 m-3, expressed as O0, O0.1, O0.3, respectively) and CO2 (400 or 800 cm3 m-3, expressed as C400 or C800, respectively). The PN declined immediately after O3 fumigation, and was larger under O0.3 than under O0.1. When C800 was combined with the O3, PN was unaffected by O0.1 and there was an approximately 20 % decrease when the rice leaves were exposed to O0.3 for 3 h. The depression of stomatal conductance (g s) observed under O0.1 was accelerated by C800, and that under O0.3 did not change because the decline under O0.3 was too large. Excluding the stomatal effect, the mesophyll PN was suppressed only by O0.3, but was substantially ameliorated when C800 was combined. Ozone fumigation boosted the RD value, whereas C800 suppressed it. An appreciable reduction of ascorbic acid occurred when the leaves were fumigated with O0.3, but the reduction was partially ameliorated by C800. The degree of visible leaf symptoms coincided with the effect of the interaction between O3 and CO2 on PN. The amelioration of O3 injury by elevated CO2 was largely attributed to the restriction of O3 intake by the leaves with stomatal closure, and partly to the maintenance of the scavenge system for reactive oxygen species that entered the leaf mesophyll, as well as the promotion of the PN. and K. Imai, K. Kobori.