| Global elevated atmospheric CO2concentration has become an indisputable fact. As one of the main substrate of plant photosynthesis, changes in atmospheric CO2concentration will inevitably affect the growth, development and physiological processes of crops. Northern Japonica rice is a main crop in north China. Climate change is happening with elevated CO2, how effects of elevated CO2on Northern Japonica rice growth and development, and how yield of Northern Japonica rice response to elevated CO2are becoming one of scientific problems to be resolved. Currently, FACE (Free Air CO2Enrichment) system is the best simulation of the future high concentrations of atmospheric CO2after Air chamber and greenhouse. Experiments were work at the CAAS’s FACE system, with two CO2concentration level (600±60ppm and389＋40ppm) and two Northern Japonica rice varieties (Songjing9and Daohuaxiang2). Research was made effects of elevated CO2on the plant morphology, soluble substances and photosynthetic pigment content in flag leaves, nutrients content and enzyme activites in grains, plant productivity. Conclusions are listed as follows:1. The research showed that the stem length to elevated CO2concentration were significantly reduced2.27%and5.05%for Songjing9and Daohuaxiang2. However, Elevated CO2concentration raised the panicle length of Daohuaxiang2, but the panicle length of Songjing9was droped under conditions of elevated atmospheric CO2concentration. The change of plant flag leaves morphology under elevated CO2in performance, increased leaf thickness, leaf width and length is reduced.2. The research results showed that elevated CO2concentration increased soluble sugar content in flag leaves for Songjing9and Daohuaxiang2obviously from booting stage to ripening stage, with the peak increase of13.80%and52.05%, respectively. Elevated CO2concentration obviously reduced soluble protein content in flag leaf except heading stage stage for Songjing9and Daohuaxiang2, which was31.69%and14.20%in the largest reduction, respectively. The results indicated that elevated atmospheric CO2concentration was with different effects on soluble sugar and soluble protein in flag leaf of different rice varieties at different growth stages. The reason is possibly that elevated CO2promotes rice growth and development, leading to an early maturity, then senescent leaf promotes soluble sugar’s decomposition, and speeds up conversion rate of soluble protein. At the grain nutrients content areas, the FACE treatment made content of protein in grains reduced by4.51%for Daohuaxiang2, made content of amylose in grains increased by3.46%for Songjing9. That explains effects of elevated atmospheric CO2concentration on the grain nutrients content exist differences between varieties.3. The research results showed as follows:Firstly, In the condition of elevated atmospheric CO2concentration, content of chlorophyll a in flag leaves for Songjing9and Daohuaxiang2were both obviously increased from booting stage to heading stage, as well as, the highest increase were28.46%and19.58%, both were decreased to15.25%and23.20%in dough stage. Secondly, in full ripeness period, the FACE treatment made content of chlorophyll b in flag leaf for Songjing9and Daohuaxiang2increased in this period, the increase were separately4.19%and9.46%, both were reduced to7.57%and5.33%in dough stage. Thirdly, in heading stage, content of Carotenoid in flag leaves for Songjing9and Daohuaxiang2were obviously increased of up to9.47%and13.55%under FACE treatment, made two varieties reduced by up to13.54%and16.67%from milky to ripening stage. Fourthly, the trend of effect of elevated atmospheric CO2concentration on total chlorophyll content and ratio of chlorophyll a/b in flag leaves for Songjing9and Daohuaxiang were consistent. It has an increasing trend from booting to heading stage, while it has a decreasing trend during dough period. Overall, it is suggested that elevated atmospheric CO2concentration promoted synthesis of photosynthetic pigment in flag leaves of northern rice before grouting, but was inhibited after grouting. At the same time, it has various degree of responsing for different varieties rice.4.The results showed that elevated CO2increased ADPG pyrophosphorylase enzyme activity in grains for Songjing9and Daohuaxiang2obviously during flowering stage, milky stage and ripening stage, with the peak increase of56.67%and21.31%, respectively. Elevated CO2concentration obviously raised starch synthase enzyme activity in grains from milky stage to ripening stage for Songjing9and Daohuaxiang2, which was36.81%and66.67%in the largest increase for soluble starch synthase, which was25.00%and36.44%in the largest increase for granule bound starch synthase, respectively. Elevated CO2concentration obviously increased soluble starch branching enzyme activity in grains for Songjing9and Daohuaxiang2during flowering stage, dough stage and ripening stage, with the largest increase of25.15%and21.33%, then obviously decreased9.96%and5.19%in milk stage. Elevated CO2concentration obviously reduced granule bound starch branching enzyme activity in grains during flowering stage for Songjing9and Daohuaxiang2, which was13.08%and5.74%in the largest reduction, respectively; elevated CO2concentration obviously raised granule bound starch branching enzyme activity in grains during milky stage and ripening stage, with the largest increase of14.14%and12.5%. The ADPG pyrophosphorylase and granule bound starch branching enzyme activity peaks to elevated CO2concentration were significantly increased21.19%and13.32%. Under the condition of elevated CO2, ADPG pyrophosphorylase enzyme activity and soluble starch synthase enzyme activity peak of the high amylose content varietie was higher, and soluble starch synthase enzyme activity and granule bound starch branching enzyme activity peaked earlier time. That explains elevated CO2promote the synthesis of starch in different extent.5. The results indicated that elevated CO2aggrandized sucrose synthase enzyme activity in grains for Songjing9and Daohuaxiang2obviously from heading stage to milky stage, with the peak increase of65.33%and61.09%, respectively. After milky stage, it distinctly reduced, with the largest reduction of6.52%and5.99%for Songjing9and Daohuaxiang2. Elevated CO2concentration obviously increased vacuolar invertase enzyme activity in grains for Songjing9and Daohuaxiang2in ripening stage, with the largest increase of31.15%and36.63%. Then cell wall bound invertase enzyme activity in grains obviously increased under conditions of elevated atmospheric CO2concentration, with the largest increase of22.61%for Songjing9in booting stage and the largest increase of44.54%for Daohuaxiang2in ripening stage. Before full heading stage elevated CO2concentration obviously increased sucrose phosphate synthase enzyme activity in grains, which was65.73%and71.94%in the largest increase for Songjing9and Daohuaxiang2. The sucrose synthase and cell wall bound invertase enzyme activity peaks to elevated CO2concentration were significantly increased27.83%and22.61%for Songjing9. However, the sucrose synthase enzyme activity peaks was obviously decreased5.99%and for Daohuaxiang2, cell wall bound invertase enzyme activity peaks was obviously increased34.27%.6. The results showed that elevated atmospheric CO2concentration boosed seed yield of individual plant, total biomass and economic coefficient with an average of9.71%,1.60%,15.44%for Songjing9, and2.22%,1.97%,31.06%for Daohuaxiang2. Simultaneously, CO2concentration made panicles per ear, seed-setting rate for Songjing9and Daohuaxiang2increased, the increase of kernel weight were separately8.6%and4.5%. This shows that effects of CO2concentration on kernel weight had significant increase trend. Meanwhile, elevated atmospheric CO2concentration increases rice plant productivity. The reason might is that elevated CO2promotes rice growth and development. |
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