Studies On Effects Of Co₂Concentration On Growth Characteristics And Yield Physiologies Of Cold Land Japonica Rice

Atmospheric CO2concentration is important environmental factor for rice production. IPCC’s reports showed a increasing trend for CO2concentration, which predicted the concentration will hit up to550μmol-mol-1in this mid of century. This condition will accelerate the impact of elevated CO2on ecosystem of plants, ecosystem. OTC (open top chamber) is applied in this study. Japonica rice of cold region will be used to research the effects of different CO2concentration on the yield, growth character and photosynthetic physiology of Japonica rice in cold region. The results showed:1. Elevated CO2induced a increase of dry matter for root, stem and grain, and for single leaf increase at first and decrease. Differences from different organs makes the root-shoot ratio and stem-leaf ratio increase, grain-straw ratio and harvest index decrease. CO2concentration increasing makes the productivity increase, valid tiller number, sub-racbis in main stem are the main factors. The productivity of CK increased15.6%under elevated CO2treatment, but not significant effects occurred under middle level of CO2concentration. Tiller number, panicle intensity, number of panicle per tiller increased, but thousand grain weight decreased significantly. The changes of productivity on sensitivity of CO2in turn were:valid tiller number, sub-rachis in main stem, averaged valid grain at sub-rachis, valid grain at first rachis according to different position responsible for changes of productivity and sensitivity of tiller structure.2. Elevated CO2induced growth process become faster, leaf-age index and heading date earlier, heading faster, flowering period earlier, filling speed faster. The heading stage shifted to72h,21h under high concentration and middle CO2compared to CK, elevated CO2accelerate averaged graining ratio, shorter high-speed graining, and2d ahead of heading stage reached up to maximum graining, the maximum graining speed increased11.5%, some at superior position increase obviously. Elevated CO2induced leaf-area index increase at first and then decrease, single leaf area reduce significantly more than leaf weight which is according to leaf age. 3. Elevated CO2induced photosynthetic rates and rnal CO2increased, stomatal conductance and transpiration decrease. Response from photosynthetic index has long term and short term effects to CO2concentration, all parameters change according to photosynthetic production increase except dark respiration rate. Averaged productivity of photosynthesis under higher CO2concentration treatments increased25.96%and19.00%under highest and middle concentration, respectively. Maximum net photosynthetic rates, dark respiration, initial quantum efficiency, saturated point of light increased, but compensate point of light decreased, maximum of nct photosynthetic rates between380-680μmol-mol-1exhibited a faster trends, after680μmol-mol-1, the speed became slower.4. Elevated CO2induced microstructure change:unit cell number increase, cell index differ obviously and impact leaf back significantly. Distance between silicon cell band cork and cork cell band increase significantly; Different cells arrange more intensely, S stomata band number increase. Elevated CO2induced the increase of silicon and cork in foliar silicon band, but the width became smaller, cellular unit areas along silicon cork band were significantly decreased, especially for cork cell mount in mastoid numbers, stoma density at foliar back showed slightly decrease, somatal index decreased significant, stoma and areas of guard cells, circumference and length increased significantly, width of guard cells and numbers of mastoid process decreased significantly. Width of stoma at segmental venter decreased significantly, as well as area, circumference.During CO2increased, Shapes of chloroplast shifted from ellipse to circular, volume of starch grain became bigger and occupying into chloroplast, foliar chloroplast and its granum and thylakoid membrane have no difference, thickness of chloroplast decreased, but granum superposition and width increased.5. Elevated CO2induced productivity cold land japonica rice increase, the main factor is increase of effective tiller number, there are big differences among different cultivars. By comparing the cultivars of different maturity, the order from high to low for productivity is early>middle> later maturity. The results by analyzing the effects of CO2concentration on productivity of cultivars at same period maturity showed, the cultivars at middle maturity stages in response to CO? showed same trends, but there are big differences among late cultivars.