A Study On Adaptability Of Torreya Grandis ‘Merrillii Hu’ And Torreya Grandis Seedlings To High Temperature Stress

Torreya grandis Fort.ex Lindl.’Merrillii Hu’（TGM）seedlingsis is an asexually propagated species of Torreya grandis Fort.ex Lindl.（TG）in the Taxaceae family,the most important species of Torreya in the world.In the process of TGM seedlings planting and spreading,extreme heat has limited its survival and growth and harms the big seedlings.Thus,this article focuses on the adaptability of TGM and TG seedlings to high temperature stress,TGM and TG seedlings of the same specification were treated under simulated outdoor high temperature（25℃,30℃,35℃,and 40℃）,The determination of TGM and TG seedlings chlorophyll content,antioxidant enzyme,antioxidant,gas exchange parameters,chlorophyll fluorescence parameters,etc,To investigate the differences of TGM and TG seedlings mechanism in response to high temperature stress,the following conclusion are reached:（1）Under high temperature stress,The Pn and Gs decreased clearly,and Ci increased significantly in TGM and TG seedlings,indicating that the decreased Pn is not due to stomatal factors in TGM and TG seedlings.The fluorescence parameters Fv’/Fm’,ΦPSⅡ,q P,Fv/Fm,ABS/CSm,TRo/CSm,ETo/CSm,ABS/CSo,TRo/CSo,ETo/CSo,PI_absand PI_totalwere slight increased or maintain stable,and was significantly decreased with increasing temperature.The degree of decreased was greater in TGM seedlings than that in the TG seedlings.DIo/CSo,DIo/CSm,DIo/RC,φDo were gradually increased with the increase of temperature,and TGM seedlings increased more than TG seedlings.These results indicated that the PSII action center’s light energy capture capacity,light energy conversion efficiency,and electron transfer quantum yield were decreased under high temperature stress,leading to a decrease in electron transfer rate,and finally a decrease in Pn in both seedlings.At the same time,in order to prevent damage to the PSII action center,the light-energy dissipation system was started.TGM seedlings has a higher dissipation capacity than TG seedlings,which effectively protects the PSII action center and makes TGM’s electron transfer and photosynthetic capacity decrease less under high temperature.（2）Under 35℃,in processing,Chla,Chlb and Car maintain stable,and O^2?-producing rate,H₂O₂and MDA,As A and GSH content,DHAR,MDHAR,GR,APX and SOD,POD,CAT activity increased gradually in TGM and TG seedlings,and the rise of TGM seedlings is greater than that of TG seedlings.But under the stress of 40℃,the leaf cells TGM and TG seedlings continue to die,the indicators of rapid decline.These results indicate that under moderate temperature TGM and TG seedlings can rapidly activate antioxidant defense system,maintain ROS balance and maintain normal physiological function of plant cells by increasing antioxidant content,As A-GSH cycle and antioxidant enzyme activity when free radicals are rapidly rising.But at 40℃,the antioxidant defense systems of both seedlings themselves were also damaged by the high temperature.Comparison of relevant data between Torreya grandis and Torreya grandis seedlings shows that under high temperature stress,torreya grandis has higher non-enzyme antioxidant content than Torreya grandis,stronger antioxidant defense system and antioxidant capacity than Torreya Grandis,and greater light energy dissipation capacity than Torreya Grandis,indicating that Torreya grandis through grafts has stronger resistance to high temperature stress than Torreya Grandis.