Impact Of Drought Stress On Ecophysiological Characteristics Of Four Varieties Of Juglans And Carya

The plants of the Juglans and Carya have strong adaptability,many uses,and high oil content.They are the most important woody oilseeds,dried fruit trees and timber trees.There are 23 and 18 species of Juglans and Carya distributed globally.There are 5 species in China(Juglans regia L,Juglans mandshurica Maxim,Juglans cathayensis Dode,Juglans sigillata Dode,Juglans hopeiensis Hu),which are distributed in the main walnut producing areas in Yunnan,Shaanxi,and Sichuan.In recent years,Carya illinoinensis 'Pawnee'(Carya)and Juglans hindsii Rehder(Juglans)from the United States have been widely introduced in various places in Sichuan,Yunnan,Henan and Shaanxi.In the southern regions of Sichuan and Yunnan,there are sometimes 7-10 days of drought in summer,which greatly affects the yield and quality of walnuts.In order to find higher drought-tolerant tree species,2-year seedlings of J.hindsii Rehder(Juglans),C.illinoinensis ‘Pawnee'(Carya),Juglans sigillata Dode(Juglans sigillata)and Juglans regia L Wanghe2(Sichuan native tree species)were treated under drought stress.These morphological index and eco-physiological indexes were investigated with a factorial experiment of varying stress time for 31 days,comparative analysis of its dynamic changes,and comprehensive evaluation using gray correlation method and membership function method.The purpose is to study the adaptability of these varieties to local drought,and further select varieties with strong drought resistance,which are used for variety improvement,ecological restoration or forest product production,and scientifically guide production practices.The results showed that,(1)Morphological adaptability of aboveground.the leaves of J.hindsii Rehde began to wither,turn yellow,and turn black,and appeared at 4 d,9 d,and 19 d after stress.After the stress treatment,the leaves of C.illinoinensis ‘Pawnee' began to wither and turn yellow on the 19 th day,and turned black on the 23 rd day.Drought stress had no significant effect on their branch and trunk morphology.The leaves of J.sigillata Dode showed wilting,yellowing,and blackening on the 4th,9 d,and 17 d of the stress treatment,and dark spots appeared on the branches and trunks on the 17 th and 28 d.J.regia L Wanghe 2 leaves withered and had yellow spots on the 9 th day under stress,black spots on the leaves on the 17 th day,black spots on the branches on the 19 th day,and black spots on the trunk on the 31 st day.(2)Adaptability characteristics of root morphology.The total root length,surface area,average diameter,volume and number of root tips of roots had no significant effect at the early stage of drought stress,but the inhibition effect increased significantly at the later stage of drought stress.The root elongation(total root length)and thickening(root surface area)of J.sigillata Dode and J.regia L Wanghe2 on the 17 th and 19 th day,and J.hindsii Rehde and C.illinoinensis ‘Pawnee' on the 19 th and 17 th day were significantly inhibited after stress treatment.The number of root tips of J.hindsii Rehde,C.illinoinensis ‘Pawnee',J.sigillata Dode and J.regia L Wanghe 2 decreased significantly on the 23 th,17 th,9 th and 14 th day after stress.Root average diameter Root volume is relatively less affected by drought stress.(3)Characteristics of biomass change.aboveground fresh weight and aboveground dry weight were decreased with the stress time longer,and aboveground fresh weight and aboveground dry weightin the control group were increased.During the whole stress process,the decrease of J.sigillata Dode was the biggest,which show that its drought resistance was the weakest.Fresh root and dry root weight increased firstly with stress time longer and then decreased,and fresh root and dry root weightin the control group were increased.At the beginning of drought stress,fresh and dry weight of roots increased,but drought did not interfere with metabolism and biomass synthesis in plants,The fresh weight of root was less than that of the control group after the 14 th day of J.regia L Wanghe 2,after the 17 th day of J.hindsii Rehde and J.sigillata Dode,after the 19 th day of C.illinoinensis ‘Pawnee',shows that the drought resistance of J.regia L Wanghe 2 is the weakest and that of C.illinoinensis ‘Pawnee' is the strongest.The dry weight of root was less than that of the control groupafter the 19 th day of J.indsii Rehde and C.illinoinensis ‘Pawnee',after the 17 th day of and J.sigillata Dode and J.regia L Wanghe 2,shows that the drought resistance of J.hindsii Rehde and C.illinoinensis ‘Pawnee' was higher than that of J.sigillata Dode and J.regia L Wanghe2.(4)Changes in physiological indicators.Roots vigor and the leaf relative conductivity were increased with the stress time longer.However,the relative water content,water potential,and SOD activities in leaves were decreased.Leaf MDA content increased firstly with stress time longer and then decreased and increased finally.Leaf soluble sugar content increased firstly and then decreased.There was a significant change of the leaf soluble sugar content and root activity of four tree species on the day 14,and day 17,respectively.The content of leaf relative water,superoxide dismutase,and malondialdehyde were changed on the day 19.The content of leaf relative conductivity and water potential of four tree species were changed significantly on the day 23.(5)Adaptive evaluation.Comprehensive morphological and physiological indicators,membership function evaluation was used to identify the drought resistance of four varieties,and the order was J.hindsii Rehder(5.033)>C.illinoinensis ‘Pawnee'(5.001)>J.regia L Wanghe 2(4.939)>J.sigillata Dode(4.856).