Effects Of Simulated Drought On Photosynthesis And Chlorophyll Fluorescence Characteristics Of Seven Camellia Oleifera Clones

Under laboratorial conditions of drought stress,the drought resistance of seven Camellia oleifera clone seedlings were evaluated synthetically using PEG-6000.The seedlings of Camellia oleifera were stressed in MS with different concentration of PEG6000?10%,20%and 30%?for 12 h,24 h,36 h and then re-water for another 12 h to investigate effects of drought on Photosynthetic and Chlorophyll fluorescence characteristics of Camellia oleifera seedlings.The results showed that:?1?Generally,photosynthesis rate of 7 Camellia oleifera clones decreased significantly under drought stress,and that of Guiwu 1,Guiwu 4 and Yueshao 77-1recovered more or less while other clones didn't after re-watering for 12 h.The stomatal conductance?Gs?of the 7 clones all decreased markedly,showing nearly no difference among clones in the same period,there was even no significant difference among Guiwu series in the same period with different degrees of drought stress.Basically,Gs didn't show a great change with more severe drought stress and couldn't even recover.The response of intercellular CO₂ concentration?Ci?to drought stress differed among series of Camellia oleifera.Drought stress caused a decline in transpiration rate of the 7 clones and 30%PEG Solution had the greatest effect.?2?Cenxi series'Fm basically increased first and then decreased.Fm of Guiwu 1 CK and 10%group decreased first and then increased with a decline after re-watering,and that of 20%and 30%increased first and then decreased with no change after re-watering.Fm of Guiwu 4 kept increasing in 20%group and showed significant increase in 30%group after re-watering.Yueshao 74-1 showed an increase followed by a decrease while 75-2 and 77-1showed no significant trend and CK showed no significant change.ETR of Cenxi 2 and Cenxi 3 reached a peak at 24 h in 10%and 20%group,10%and 20%increased first and then decreased basically.ETR of Guiwu 1 and 4 in 10%,20%and 30%group increased after 36 h drought stress,and for Guiwu 1,10%,20%and 30%group decreased after re-watering while for Guiwu 4,20%and 30%group increased.ETR of Yueshao series under stress was almost entirely lower than CK except 77-1 at 12 h.For Y?NPQ?of Cenxi2,differences only occurred at 24 h,and for Cenxi 3,there was also no significant difference between 12 h and 36 h.NPQ of Guiwu 1 showed no significant difference in 12h group and CK,10%and 20%group increased after 36 h and re-watering didn't make great difference.For Guiwu 4,NPQ kept decreasing in CK and 30%group as stress continued,while 10%and 20%group kept increasing,and all increased after re-watering.20%group was always the peak of NPQ for Yueshao 74-1 and 75-2,while the maximum of77-1 appeared in CK group.The tend of NPQ is about the same as that of NPQ.?3?Considering all the above,this paper used PCA to evaluate the drought resistance of 7 Camellia oleifera clones and the conclusion could be showed in the following sequence of drought resistance:Yueshao 74-1>Yueshao 75-2>Yueshao 77-1>Cenxi 2>Cenxi3>Guiwu 1>Guiwu 4,and that means Yueshao 74-1 has the greatest drought resistance among the 7 clones and the drought resistance of native Yueshao series of Guangdong is generally better than those from Guangxi.