Effect of Temperature Return Rate on Photosystem Activity of Camellia oleifera During Recovery from Low-temperature Stress

In this study, the effects of low-temperature stress and different temperature return rates on the activity of photosystem Ⅰ( PS Ⅰ) and photosystem Ⅱ(PS Ⅱ) of Camellia oleifera were investigated. The 2-year-old potted seedlings of C. oleifera 'Changlin40' were used as the test material. After being stressed at low temperature(−5 ℃) for 24 hours, the temperature was heated to room temperature(25 ℃) at rates of 30, 5, 2.5 ℃/h. The rapid induction kinetic curves of chlorophyll fluorescence and the redox kinetic curves of P 700⁺ were determined, and the chlorophyll fluorescence was quenched. The findings revealed that after 24 hours of low-temperature stress, photoinhibition of PS Ⅱ and PS Ⅰ activities of C. oleifera leaves occurred to different degrees. In the recovery stage, both PS Ⅱ and PS Ⅰ activities are sensitive to the return temperature rate, and PS Ⅱ activity accelerates with the increase in the return temperature rate. At the same time, PS Ⅰ activity recovers slowly at the fast return temperature rate(30 ℃/h) and faster at the slow return temperature rate(2.5 ℃/h). Rapid temperature rise promotes the recovery of linear electron transfer rate in C. oleifera leaves. The faster the temperature rises, the more electrons are transferred from PS Ⅱ to PS Ⅰ during the recovery process. The excessive number of electrons decreases the oxidation level of P 700, which further intensifies the photoinhibition of PS Ⅰ. In the recovery process of C. oleifera under low-temperature stress, the acceleration of PS Ⅱ activity recovery at a faster temperature return rate will lead to an increase in photosynthetic electrons flowing to PS Ⅰ, further aggravating the mismatch between PS Ⅱ and PS Ⅰ activities. Measures should be taken to prevent the temperature from rising too fast after the occurrence of low temperature in production, to facilitate the protection and repair of C. oleifera photosystem.