农牧交错带油葵光合作用日变化及午休现象的研究

A study on diurnal variation in photosynthesis and midday depression phenomenon of photosynthesis of oil sunflower in agro-pastoral ecotone

为了解农牧交错带油葵旺盛生长季光合作用日变化特征和光合"午休"原因,使用光合作用测量系统(LI-6400XT)于内蒙古武川试验站(2013年7月24日—7月28日)测定了晴天条件下油葵光合特性。结果表明:油葵光合速率日变化呈现典型的双峰曲线,具有明显的"午休"现象,且上午的峰值显著高于下午的峰值,观测期间平均高出11%。对油葵光合速率有显著影响的气象因子是光强和温度。蒸腾速率和气孔导度的日变化规律相似,也呈现双峰曲线,并且两者的峰值要早于光合速率的峰值。对气孔导度有显著影响的气象因子是光强和饱和水汽压差,对蒸腾速率有显著影响的气象因子是光强、饱和水汽压差和温度。油葵叶片的水分利用效率最高值出现在11:00,最高值为2.71g/kg。观测期间,在油葵光合速率下降的阶段均表现为胞间CO2浓度增加,气孔限制值下降。因此,造成该地区油葵光合"午休"的主要因素是非气孔因素。

In order to explore the diurnal variation in photosynthesis and midday depression phenomenon of photosynthesis of oil sunflower(Helianthus annuus)in agro-pastoral ecotone,the leaf photosynthetic rate,the transpiration rate and the stomatal conductance of oil sunflower were measured using the LI-6400 XT Portable Photosynthesis System during the stage of flower bud from July 24 to July 28,2013 in Wuchuan Experimental Station of Inner Mongolia.The study results showed that the diurnal variation in the leaf photosynthetic rate of oil sunflower appeared a typical bimodal curve in accompany with the obvious midday depression phenomenon of photosynthesis.In general,there were two peaks in diurnal variation in the leaf photosynthetic rate of oil sunflower with higher value in the morning than that in the afternoon.Light intensity and air temperature had a significant impact on the leaf photosynthetic rate of oil sunflower.The diurnal variations of the leaf stomatal conductance and the leaf transpiration rate also showed bimodal curves with earlier occurrence of the first peaks than the leaf photosynthetic rate.Light intensity,vapor pressure deficit(VPD)and air temperature affected the leaf transpiration rate of oil sunflower significantly,light intensity and VPD affected the leaf stomatal conductance significantly.The intercellular CO2 concentration increased but the stomatal limitation value decreased during the stages of midday depression of photosynthesis.Therefore,the midday depression of photosynthesis of oil sunflower was caused by non-stomatal factors.