Effect Of An Extreme High Temperature On Photosynthetic Characteristics In Magnolia Sinostellata

The Magnolia sinostellata was an ornamental shrub of Magnoliaceae,which was found narrowly in high altitude areas in Lishui County,Zhejiang Province,China,and now facing the challenge of extinction.Moreover,no tree was found in urban landscape.Now,we hoped that M.sinostellata could be widely used in landscape designing.However,extreme high temperature was one the factors of environment which affected the development of plant.Therefore,the samples of M.sinostellata were put in high temperature stress,and physiology parameters,photosynthetic parameters,photosynthetic enzyme and Photosynthetic metabolites of leaves were detected.All results showed as following:(1)The morphology was no significant different between CK and 40? before 12 h,and some leaves on the top of tree appeared wilt phenomenon at 24 h.Then wilting phenomena at 48 h was more serious than 24 h.As arrived 72 h,the top leaves were dropped and about 1/3 leave area had black pots.At 120 h finally,2/3 leaf area became black and wilting was more obvious.(2)As the time increasing,electric conductivity content and MDA content of M.sinostellata were growing(p<0.05),and arrived the highest at 48 h,then declined under 40? condition.Moreover,all content were higher than CK.These indicated that heat stress destroyed the membrane system.(3)As the plant was in one condition,there was one adaption process before 24 h.The results of photosynthetic parameters showed that the value of Pn and WUE of M.sinostellata was climed the highest at 48 h,but Gs,Ci,Tr was lowest.The correlation analysis showed that the relationship between Pn and Ci is negative correlation,which indicated that the stomatal limitation was the main reason of the Pn falling.(4)During 40? condition,the values of Fo,Fm,Fv,Fv/Fm,Fv/Fo,Fv'/Fm' and qP were all lower than CK.The ?PSII and ETR increased and got top at 48 h,then decreased sharply.So the results explained that M.sinostellta under high temperature protected the photosynthetic apparatus by higher photochemical and non-photochemical pathway.(5)Under heat temperature,the activity of Rubisco was decreasing from 12 h,and FBPase was from 24 h.There was however no obvious change of SPS.At the same time,the content of Sucrose,glucose and fructose was higher than CK at 48 h,and the content of starch was also higher.That allindicated that under high temperature affected the sugar metabolism pathway.(6)The results of principal component analysis showed that 24 idexes were divided to 4 componets.The first was Pn,Ci,WUE,Fo,?PSII;the second was FBPase,starch,glucose,the third was Fm and Fv;the forth was Rubisco,which all stated that these indexes can explain the tolerance of M.sinostellata.Accordingly,the morphology,cell membrane system,photosynthetic system and sugar metabolism of M.sinostellata were destroyed by heat stress.We however also found that M.sinostellata could bear high temperature in short period,and 48 h was the limited time in 40? condition basing on the results of photosynthetic response.Therefore,M.sinostellata can be used in the landscape designing of city.This conclusion will do not only enhance the quantity of M.sinostellata,but also make M.sinostellata to be protected.