The Influence Of Different Nitrogen Application And Nitrogen Forms On Photosynthetic Characteristics

The net photosynthesis rate (Pn), stomatal conductance (Gs), water use efficiency (WUE) and photosynthesis nitrogen use efficiency (PNUE) was compared between two rice cultivars (Oryza sativa L.): Liangyoupeijiu (LY) and Shanyou 63 (SY).We also investigated the effect of endogenous carbohydrate on Pn, Gs and intercellular carbon dioxide concentration (Ci) of leaves of rice. The result showed that:1. There is little difference between the Pn of leaves under high and low amount of urea before heading. But 10 days after heading, the Pn of leaves under high amount of urea was higher than that under low amount of urea, and this difference became more distinct especially 30 days after heading. During senescence stage, LY has higher Pn than that of SY. With the development of seed, the Pn of LY decreased more slowly than that of SY.2. After heading stage, the Ci of leaves under low amount of urea was higher than those of other treatments. And the stomatal conductance of leaves under low amount of urea was higher than that under high amount of urea. The leaves of rice under high amount of urea, had higher WUE than that under low amount of urea. After heading, the WUE of LY was higher than that of SY.3. Under different nitrogen forms treatment, the Pn of leaves with urea treatment was the highest. After heading, the Pn of leaves with NH+-N as N source was higher than that with NO3-N as N source. The Ci of leaves with urea as N source was lower than that of other treatments, while there is little difference between the Ci of leaves under NH4+-NO3 and NO3-NH4 as N source.4. The Pn and Gs of leaves of rice has close correlation. From the Gs-Pn curve of leaves of SY, we can deduce that Pn would not rise when Gs was higher than 5mol H2O m-2 s-1, but no similarity was observed in LY. The relationship between Gs and Pn with different N treatment was analogous.5. The PNUE of leaves with high amount of N was higher than that under low amount of N. After heading stage, the PNUE of leaves of LY were higher than those of SY. There was no obvious difference between the PNUE of leaves of SY under NH4+-NO3 and NO3-NH4+ as N source after heading stage. As for LY, the PNUE of leaves under urea treatment was higher than the other treatments, and the PNUE of leaves under NH4+ treatment were higher than those under NO3- treatment.6. The Pn, Ci and Gs of leaves decreased with the increase of endogenous sucrose concentration. And there was no correlation between total soluble sugar and Pn of leaves. The Pn of leaves of WYJ was more sensitive to endogenous sucrose than other two rice cultivars. With the accumulation of starch, the Pn and Gs of leaves of WYJ increased a little. The increase of endogenous sugar concentration has no obvious influence on light compensation point of leaves, while reduced the light saturation point.7. The CO2 compensation concentration and CO2 saturation concentration of leaves of SY with urea as N source were the highest, and those with NH4+-NO3" as N source were the lowest. Low application of urea reduced COa compensation concentration and CO2 saturation concentration of leaves, and also reduced the CE of leaves. The results of LY were similar to those of SY.8. The rg and rm' of leaves of SY was lower than the other treatments, while there was little difference between those of NH-NO and NO-NH treatment. Low application of urea could increase the rg and rm of leaves. The results of LY were similar with those of SY. Application of urea could reduce light compensation point, and increase light saturation point. Low urea treatment could reduce both light compensation and saturation point.