Effects of light intensity on photoinhibition in pepper seedlings treated under low temperature and poor irradiance

Simulating unfavorable conditions of sunlight greenhouse in deep winter, and using chlorophyll fluorescence as probe, the effects of light intensity on photoinhibition in two cultivars of pepper treated under low temperature and poor irradiance stress different in susceptibility were investigated. The objective of this study was to put forward bases on which suitable measures could be taken to control optimal light intensity in greenhouse. The results showed that no photoinhibition occurred in chilling and poor light-tolerant jiamusi treated under low temperature (15℃/5℃, day/night) and poor irradiance (100 μmol·m-2·s-1, 12h photoperiod) for 1～7 days. But photoinhibition occurred in chilling and poor light-sensitive longjiao No.6 after 3 days treatment under the same conditions. Fv/Fm in both cultivars of pepper treated under low temperature and poor irradiance for 1～7 days, and then irradiated under room temperature and 300～1200 μmol·m-2·s-1 light conditions for 4 hours decreased. Fv/Fm in longjiao No.6 leaves treated under low temperature and poor irradiance for 1～3 days, and then irradiated under room temperature and 300 or 600 μmol·m-2·s-1 light conditions for 4 hours, or in Jiamusi leaves treated under low temperature and poor irradiance for 1～5 days, and then irradiated under room temperature and 300～1200 μmol·m-2·s-1 light conditions for 4 hours made a recovery in weak light, indicating that no irreversible photodamages occurred in these leaves. But Fv/Fm in longjiao No.6 leaves treated under low temperature and poor irradiance for 1～3 days, and then irradiated under room temperature and 800 or 1200 μmol·m-2·s-1 light conditions for 4 hours , or in longjiao No. 6 leaves treated under low temperature and poor irradiance for more than 5 days, or in Jiamusi leaves treated under low temperature and poor irradiance for more than 7 days, and then irradiated under room temperature and 300～1200 μmol·m-2·s-1 light conditions for 4 hours could not recover in weak light, suggesting that irreversible photodamages occurred in these leaves. From these results, it was deduced that chilling treatment under low irradiance enhanced susceptibility to photoinhibition in both cultivars at room temperature under 300～1200 μmol·m-2·s-1 irradiance for 4 hours. The longer the chilling treatment under low irradiance and the stronger the irradiance，the more severe the photoinhibition. Compared with Jiamusi, Longjiao No. 6 experienced more severe photoinhibition.