Adaptive Mechanisms Of Photosynthesis To Irradiation Time Under Strong Light In Maize Seedlings

Light is one of the important environment factors affecting plant photosynthesis.The mechanisms of plant photosynthesis adapting to strong light has been studied extensively,but previous studies mainly focused on the adaptation of photosynthesis to different strong light,while little attention have been paid to the possible effects of irradiation time.In fact,light stress includes two aspects of light intensity and irradiation time at least.We speculate that light irradiation time may affect the adaptation strategies and mechanisms of photosynthesis under strong light.So,we tried to explain the mechanisms of different light irradiation time to affect photosynthesis adaptation in maize.In this experiment,weak light(200?mol/m2/s)was used as background light,and strong light(1600?mol/m2/s)with different time was added on weak light.The results showed that the plant height,leaf area,leaf thickness and specific leaf weight of maize were significantly increased with the extension of strong light irradiation time,while leaf relative water content,pigment content(unit dry weight)and chloroplast area ratio decreased significantly.With the increase in the time of strong light irradiation,the photosynthetic rate,stomatal conductance,transpiration rate and water use efficiency were significantly increased,the apparent quantum yield changed little and the stomatal limitation increased.With the extension of strong light irradiation time,the proportion of the excitation energy allocated to the photochemical reaction of the photosynthesis system II in the absorbed light is reduced,the efficiency of the antenna conversion is decreased,the heat dissipation capacity is greatly enhanced,the activity of the antioxidant enzyme is improved,and the degree of photoinhibition is gradually reduced.Based on the above research,the main conclusions are as follows:(1)With the extension of strong light irradiation time,maize plant height increased fast,followed by leaf thickness,while the leaf area had a substantial increase only with longer strong light irradiation time;(2)Under strong light,improving photosynthetic capacity,enhancing heat dissipation and antioxidant enzyme activity were important mechanisms for maize to adapt to the extension of strong light irradiation time;(3)In the case of short strong light irradiation time conditions,maize leaves tended to improve the photosynthetic capacity and allocated more light energy to photosynthetic carbon assimilation;and the enhancement of the photoprotection ability required a relatively longer strong light irradiation time.