| The paper aimed to improve the seed germination percentage of Phoebe hui and the drought resistance of seedlings,and solve the problems of low seed germination percentage and damage to seedlings caused by seasonal drought during the cultivation of Phoebe hui seedlings.In this paper,the fresh Phoebe hui seeds and the two-year-old Phoebe hui seedlings were used as experimental materials.The paper planned to explore seed dormancy characteristics,seed physiological response under cold stratification,seedling response mechanism to drought and rehydration after drought the response,and seedling response mechanism to drought and rehydration after drought the response to Spd which can provide scientific basis for conservation and cultivation of precious broad-leaved tree species.The paper measured seed characteristics,seed germination physiological characteristics,and seedling growth,photosynthesis,fluorescence and physiological indicators.The main results are as follows:(1)The seed embryo was completely filled with the embryo cavity,and the seeds had a good water permeation ability.However,the testa restricted the seed gas exchange and hindered seed germination.The Phoebe hui seeds contained germination inhibitory substances.Therefore,Phoebe hui seeds belonged to physiological dormancy.Cold stratification can break the physiological dormancy of Phoebe hui seeds.The seeds stratified for 60 days completed germination within 40 days,and the germination rate reached 90.00%.Besides,the seeds treated with GA3 solution could promote germination.The effect of 900mg/L GA3 was the best,and the germination rate reached 67.50%after 50 days.However,cold stratification had a better effect in promoting seed germination than GA3 treatment.(2)The seed contents,enzyme system and endogenous hormones jointly promoted seed germination in the process of cold stratification.After 60 days cold stratification,the respiration rate increased to 4.13 times that of 0 day of cold stratification.The amylase activity in the seeds increased by 86.49%compared with the seeds stratified for 0 day,and the starch was continuously hydrolyzed into soluble sugars,which provided respiration substrate and energy for seed germination.The POD could put the pentose phosphate pathway of respiration in a relatively dominant position by increasing activity,which was conducive to the effective utilization of energy.Besides,the improvement of CAT activity and SOD activity could effectively remove reactive oxygen species generated during seed germination,and protect the cell structure of seeds.After 60 days cold stratification,the germination inhibitor ABA decreased by 49.90%,and the germination promoters GA3,IAA,and ZR were 2.10 times,2.00 times,and 1.25 times that of the seeds with 0 day stratification,respectively.(3)The growth,photosynthesis,photochemical reaction efficiency and physiological activity of Phoebe hui seedlings were inhibited under drought stress.Phoebe hui seedlings suffered the most inhibition under severe drought stress.Under drought stress,the seedling height growth,ground diameter growth and biomass accumulation were inhibited.The aerial part growth of seedlings slowed down.Compared with the control group,the root to shoot ratio of the severe stress treatment group was significantly different,and increased by 11.76%.Pn,Tr,Cond,WUE were significantly reduced,and Ls was significantly increased.Besides,the seedlings protected themselves through thermal energy dissipation to maintaining the intensity of photosynthesis.Fm,Fv/Fm,qP,Y(Ⅱ),and ETR continued to decrease,and Fo,Y(NPQ)gradually increased.The content of SS,SP,and Pro accumulated rapidly to maintain the osmotic balance.The MDA content gradually increased.The SOD activity increased in the early stage to reduce the damage caused by free radicals when the system was damaged by drought stress,and the SOD activity decreased in the later stage,because the physiological function of the seedlings was disordered.The chlorophyll content first increases and then decreased because the chloroplast structure was gradually destroyed.(4)Phoebe hui seedlings had good drought resistance and recovery ability,and the seedlings under mild drought stress had the best drought resistance and recovery ability.Pn,Tr,Cond,WUE,and Ls of Phoebe hui seedlings under the three drought stress levels could gradually recover,and there were still differences between them and the control group at the later stage of rehydration.However,Fo,Fm,Fv/Fm of seedlings under various drought stress levels could quickly recover to the control level at the early stage of rehydration,and qP,Y(Ⅱ),ETR,and Y(NPQ)had little difference with the control group at the later stage of rehydration.The MDA content,SOD activity,SS content,SP content,Pro content,and chlorophyll content of seedlings under mild stress could all returned to the control level in the later stage of rehydration,but some physiology indicators of seedlings under moderate stress and severe stress still differed from the control group.(5)Spd spraying can alleviate damage caused by drought stress to Phoebe hui seedlings.Among them,the seedlings sprayed with 10mg/L Spd had the best drought resistance.Spd could help seedlings maintain aerial parts accumulation.Among them,the seedlings sprayed with 10 mg/L Spd had the best growth conditions,and seedling height increment,ground diameter increment,leaf biomass,stem biomass,root biomass and total biomass increased by 22.59%,66.67%,5.35%,6.08%,2.22%,4.15%compared with the control.At the same time,Spd could better maintain the photosynthesis and chlorophyll fluorescence of seedlings.The chlorophyll fluorescence was dominant in the early drought period,and there was little difference from the control group in the late drought period. |
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