大气CO2浓度升高对干旱条件下冬小麦叶片光合适应的影响

大气CO₂浓度升高是全球气候变化的主要特征,但大气CO₂浓度长期升高条件下冬小麦叶片发生光合适应的机制尚不十分清楚。本研究以盆栽冬小麦‘郑麦9023’为试验材料,在人工气候控制室内设置2个CO₂浓度(400和600 μmol·mol^-1)、2个水分条件(田间持水量的80%±5%和55%±5%),测定拔节期和抽穗期的光合特征曲线、叶绿素荧光动力学参数、叶氮含量和收获后的籽粒产量等指标,探讨干旱条件下库源关系改变对叶片光合适应的影响。结果表明: 在小麦拔节期,干旱条件下CO₂浓度升高处理的小麦PSⅡ实际光化学效率没有显著增加,但通过提升最大电子传递速率和电子向光化学方向的传递比例,增强了Rubisco的羧化速率,从而提高了最大净光合速率;在抽穗期,功能叶最大电子传递速率和电子向光化学方向的传递比例虽然较高,但PSⅡ实际光化学转换效率降低,Rubisco羧化速率和丙糖磷酸利用效率下降,以致最大净光合速率降低。干旱条件下,CO₂浓度升高增加了小麦单茎生物量、单穗粒数和穗粒重,降低了不孕小穗数,提高了籽粒产量。土壤干旱条件下,CO₂浓度升高对收获期小麦单茎籽粒产量的促进作用可能主要来自于生长前期的光合产物积累。生长后期光合适应发生的主要原因是功能叶PSⅡ实际光化学转换效率和丙糖磷酸利用效率的降低,而不是最大电子传递速率、光化学方向的电子传递比例和新叶库强的变化。

Effects of elevated CO2 concentration on photosynthetic acclimation of winter wheat under drought condition

Mechanisms underlying leaf photosynthetic acclimation in winter wheat under elevation of CO₂ concentration (CO₂]) remain unclear. The aim of the study was to investigate the effects of source-sink variation on photosynthetic acclimation induced by drought under elevated CO₂]. A winter wheat (Triticum aestivum L. ‘Zhengmai 9023’) pot experiment was conducted in open top climate chambers with CO₂] of 400μmol·mol^-1 or 600 μmol·mol^-1 and soil water content at 80%±5% or 55%±5% of field capacity. The parameters of chlorophyll fluorescence, electron transport rate, photosynthetic curve, leaf nitrogen content, and grain yield were measured at the elongation and heading stages. Under drought condition, leaf PSⅡ photochemical efficiency was not affected by elevated CO₂], but the maximum electron transport rate and the ratio of electron partitioned to carboxylation reaction in Calvin cycle was increased at the elongation stage, and thus the Rubisco carboxylation rate and maximum photosynthetic rate were increased. Although the maximum electron transportation rate and partitioning ratio of electron to carboxylation reaction in Calvin cycle remained high at the heading stage, the PSⅡ photochemical efficiency, Rubisco carboxylation rate, and triose phosphate utilization rate were decreased by elevated CO₂], which consequently reduced the maximum photosynthetic rate for plant under drought stress. Under drought condition, elevated CO₂] increased wheat tiller biomass, kernel number, and kernel weight per ear, but decreased infertile kernel number, resulting in an overall increase in grain weight. In conclusion, the elevated CO₂]-induced increase in wheat grain yield per tiller under drought condition was mainly caused by enhanced photosynthetic performance at the elongation stage. The photosynthetic acclimation in source leaves during the heading stage under elevated CO₂] was mainly attributed to the reduction in PSⅡ photochemical efficiency and triose phosphate utilization rate, but not to the maximum electron transportation rate, ratio of electron partitioned to carboxylation in Calvin cycle or sink leaf strength.