大气二氧化碳(CO_2 )浓度增高导致全球变暖,但作为光合作用底物促进绿色作物的光合作用。为了明确高CO_2浓度对杂交水稻结实期光合日变化的影响, 2014年利用稻田FACE(Free Air CO_2 Enrichment)平台,以生产上曾创高产纪录的两个杂交稻新组合甬优2640和Y两优2号为供试材料,设置环境CO_2和高CO_2浓度(增200 mumol /mol)两个水平,测定杂交稻抽穗期和灌浆中期光合作用日变化和成熟期生物量。结果表明,高CO_2浓度环境下两组合抽穗期叶片净光合速率均大幅增加(全天平均52%),但灌浆中期的平均增幅减半,其中Y两优2号这种光合下调表现更为明显。大气CO_2浓度升高使两杂交稻组合抽穗和灌浆中期叶片气孔导度均大幅下降,导致蒸腾速率下降而水分利用效率大幅增加,Y两优2号气孔导度和蒸腾速率对CO_2的响应上午大于下午,而甬优2640表现相反。尽管大气CO_2浓度升高使杂交稻结实期不同时刻胞间CO_2浓度均大幅增加,但对气孔限制值特别是胞间CO_2与空气CO_2浓度之比多无显著影响,两品种趋势一致。大气CO_2浓度升高对甬优2640地上部生物量及其组分的影响明显大于Y两优2号,CO_2与品种间多存在互作效应。以上结果表明,与甬优2640相比,Y两优2号最终生产力从高CO_2浓度环境中获益较少可能与该品种生长后期存在明显的光合适应有关,但这种光合适应似乎不是由气孔限制造成的。
英文摘要:
The rising of atmospheric carbon dioxide (CO_2 ) concentration has been blamed for global warming,but it promotes the leaf photosynthesis of crops because CO_2 is the main substrate for photosynthesis. In order to understand the effect of elevated CO_2 concentration on diurnal courses of CO_2 uptake of hybrid rice,a paddy field experiment utilizing free air CO_2 enrichment (FACE) technology was undertaken to determine diurnal courses of leaf photosynthesis at heading and middle grain filling stages,and its association with the final productivity of rice at maturity. Two hybrid rice variety Yongyou 2640 (YY 2640) and YLiangyou No.2 (YLY 2) were grown in the ambient CO_2 and the elevated CO_2 concentration (200 mumol /mol above ambient) from plant transplanting until grain maturity. Elevated CO_2 concentration significantly increased net photosynthetic CO_2 assimilation of flag leaves of two hybrids by 52% on average at heading,but the enhancement was reduced to half at the middle grain filling stage. This photosynthesis acclimation was more pronounced in YLY 2. Elevated CO_2 concentration significantly decreased stomatal conductance of two hybrids at both heading and grain filling stages, resulting in lower transpiration and higher water use efficiency. Greater CO_2 responses of leaf transpiration and stomatal conductance were observed in the morning for YLY 2,but YY 2640 showed higher CO_2 effects in the afternoon. Growth at elevated CO_2 concentration significantly increased intercellular CO_2 concentration,but had no clear effects on the ratio of intercellular to air CO_2 concentration and stomata limitation value,and the same trend was observed for the two varieties. The CO_2 effects on the above-ground biomass and its components were greater in YY 2640 than YLY 2,and it was reflected in the significant CO_2 by variety interactions. The results indicated that compared with YY 2640,the lower CO_2 gain on final productivity of YLY 2 might result from photosynthesis acclimation at the late growth stage,and this down-regulation in leaf photosynthesis was not caused by stomatal limitation.