| 1. Results of photosynthetic carbon metabolism showed that, the photosynthetic rate of rapeseed leaf was promoted by high atmospheric CO2concentration, and the photosynthetic acclimation was not appeared. Under the high atmospheric CO2concentration, CO2concentration in the intercellular space (Ci) and instantaneous water use efficiency (WUE) increased, but the stomatal conductance (Cd) and transpiration rate (Tr) declined. Among of them, high CO2concentration played a more obvious promotion effect on leaf Pn and Ci. Regardless of the CO2concentration levels, N application could improve leaf Pn and WUE, and reduce leaf Ci、Cd and Tr at seedling stage. The variation tendency of photosynthetic characters (Pn、Ci、Tr、WUE) at flowering stage, when the high CO2concentration environment went back to natural atmospheric CO2concentration condition, was opposite to the results at seedling stage, while the Cd variation tendency was consistent at two stages, under the condition that CO2concentration in leaf chamber was800μmol·mol-1. High atmospheric CO2concentration could less affected leaf chlorophyll content, but increase soluble sugar content of leaf. N application could significantly increased leaf chlorophyll content, but less affected soluble sugar content of leaf. Taken together, high atmospheric CO2concentration could promote photosynthetic carbon metabolism, thus enhancing instantaneous water use efficiency. Nevertheless, the above processes were related to CO2concentration increase in the intercellular space and carbon metabolism enhancement, but had nothing to do with leaf chlorophyll content. The phenomenon of light adaptation arised after seedling stage.2Results of nitrogen metabolism in rape plant showed that, elevated CO2reduced nitrogen content in rape seeds, stem and root system. But owing to biomass increase, nitrogen-accumulated amount in each organ together with single plant also exhibited the increased trend. Regardless of the level of CO2concentration, N application could significantly increase nitrogen content of various organs and nitrogen-accumulated amount. Under high CO2condition, the nitrogen uptake efficiency, nitrogen use efficiency and nitrogen efficiency exhibited the increasing trend from seedling stage to silique-developing stage, whereas they were the opposite trend at harvest stage. The nitrogen uptake efficiency and nitrogen use efficiency tended to increase during each growth stage of rape, but N use efficiency only increased significantly at seedling stage. N application increased the nitrogen uptake efficiency, but reduced nitrogen use efficiency and nitrogen efficiency significantly. Under high CO2condition, the free amino acid and nitrate contents decreased, but the glutamine synthetase activity (GSA) increased at seedling stage. The variation of the above indicators were not consistent during other growth stages of rape, remained to be further study. Altogether, high CO2conditions reduced nitrogen metabolism in rape plant, but the nitrogen efficiency still improved because of increase of dry matter accumulation. The phenomenon of light adaptation arised at bolting stage.3. Results of agronomic traits in rape plant showed that, elevated CO2could significantly promote dry matter accumulation. The aboveground biomass increased considerably at early period of rape growth, while underground dry matter largely during late period; Likewise, N application could enhance dry matter accumulation. Elevated CO2concentration could promote the plant height, leaf length/width ratio, diameter of root and stem as well as root/shoot ratio, while N application decrease root/shoot ratio, increase diameter of root and stem. The leaf length/width ratio increased with N application level enhancement at seedling and bolting stages, but declined during flowering and pod development stages. In short, the high atmospheric CO2concentration could promote rape growth and increase dry matter accumulation.4. Results of rape yield components and yield showed that silique number increased at two N application levels under high atmospheric CO2concentration, and the grains in each silique as well as TKW (thousand kernel weight) declined under no nitrogen condition, and increased under N application condition. Besides, the actual yield and harvest index exhibited the declined trend under high atmospheric CO2concentration condition, and the rapeseed yield of non-nitrogen treatment declined more obviously than that of nitrogen treatment. The analysis of significant difference among different CO2concentration treatments demonstrated that there was significant difference in silique number, grain number per silique of rape variety B and TKW and harvest index of two rape varieties under no nitrogen condition, but not significantly different in actual rape yield. Nitrogen fertilizer application could improve silique number, theoretical yield, actual yield and harvest index, and grain number and TKW decreased under natural atmospheric CO2concentration, while improved under high CO2concentration. In conclusion, the grain yield of rape exhibited the declined trend due to reduction of grain number per silique and TKW, and it was obvious increasingly under nitrogen fertilizer application condition.5. Results of rape quality showed that high CO2concentration could not affect rapeseed oil content, and the oil content displayed declined trend without little significant difference; Nitrogen fertilizer application could remarkably increase rapeseed oil content under any CO2concentration. The contents of oleic acid and arachidonic acid declined dramatically, while linoleic acid and linolenic acid contents increased significantly under the increased CO2concentration condition, other quality indicators varied without significant difference. The difference of fatty acid content among different nitrogen fertilizer application treatments increased when CO2concentration boosted, exhibiting significant differences in treatments under high CO2concentration, but little difference under natural CO2concentration. The law of fatty acid content among treatments was obscure, remined to be further study. In summary, high CO2concentration could not decline oil content, but increase contents of some essential fatty acids such as linoleic acid and linolenic acid. Meanwhile, the difference of fatty acid content among different nitrogen fertilizer treatments was obvious under high CO2concentration. |
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