Abstract:

Objective: In this study,5-year-old European spruce(Picea abies) seedlings were used to evaluate the thermal stability and self-repairing ability of PSⅡ in the future climate warming. Method: Three clones,10 ramets of each clone,30 ramets in total,were selected and cultured in an artificial climate chamber under normal conditions. Two weeks later,hand-PEA and image-PAM were used to detect the fluorescence parameters and image of leaves as control. After preheating for 5 hours in a low light incubator at 38℃,seedlings were heated for 30 minutes at 40,42,43,44,46,48,50,52,53 and 54℃,respectively. Three clones(one ramet per clone) were treated in each experimental group. Hand-PEA and image-PAM were used to detect the fluorescence parameters of leaves and two critical temperatures of tress were selected. Seedlings treated under two critical temperatures were cultured in an artificial climate chamber for two weeks. Hand-PEA and image-PAM were used to detect the fluorescence parameters and images of leaves,and to study the self-repairing ability of spruce PSⅡ after heat shock. Result: 1) Through the study of Y(Ⅱ),Y(NO) and Y(NPQ) fluorescence images and kinetic curves,it was found that under 44 ℃ heat stress,PSⅡ of P. abies reached the initial stress temperature,and under 52 ℃ heat stress,it reached the maximum stress temperature. Compared with herbs,other woody species and related species,the thermal stability of PSⅡ was at a higher level for P. abies. 2) The fluorescence parameters of F₀,F_m,F_v/F_M,NPQ,q_L and q_P of PSⅡ and the fluorescence kinetic parameters of NPQ,q_L and q_P were detected by image-PAM at critical temperature: the fluorescence kinetic parameters of F_m and F_v/F_m were weakened,the fluorescence images of q_L and q_P were enhanced,and the fluorescence kinetic parameters of NPQ,q_L and q_P were higher than those of the control at 44 ℃. The fluorescence kinetic curves of F_v/F_m,q_L and q_P were lower than those of the control. 3) The hand-PEA was used to further detect the change of fluorescence parameters of PSⅡ. Under 44 ℃ short-time heat shock,F_v/F_m and OJIP curves did not change significantly,PI_ABS decreased only to 79.5% of the control group. The ability of chlorophyll(Chl) to absorb and capture light energy,the transmission of electrons,and the activity of center protein in electron transfer chain were not significantly inhibited. The heat chock also promoted the ability of Chl to absorb energy(ABC) photochemical reaction and fluorescence quenching. However,under the short-term heat shock of 52 ℃,the function of PSⅡ was obviously inhibited,and the OJIP curve also showed a large "K" band,F_v/F_m was reduced to 63.2% of the control group. PI_ABS was only 6.6% of the control group. The absorption and capture of light energy,photochemical reaction,fluorescence quenching and electron transfer ability of chlorophyll(Chl) were severely inhibited at the moment of F_m,and the oxygen evolution complex(OEC) of electron transfer chain was also severely damaged. Therefore,it was predicted that increasing temperature mainly inhibited the activity of reaction center and electron transfer on receptor side of PSⅡ in leaves,changed the energy flow and distribution in PSⅡ reaction center. But it had little effect on the donor side of PSⅡ. 4) After two weeks of recovery in normal growth condition,the fluorescence parameters and images of the needles of the seedlings that were previously subjected to heat shock under the two stress temperatures were restored to the level of the control,indicating that P. abies had a strong recovery ability to the short-term stress. Conclusion: Therefore,we predict that PSⅡ of P. abies has a strong elastic adaptation physiological mechanism to cope with the short-term high temperature in extreme weather at noon under the future climate change,and its temperature range of heat shock stress can be withstood that is 44-52 ℃.

Key words: Picea abies, PSⅡ, fluorescence parameters and images, heat shock stress, critical temperature