| The increasing demand in precious timber resources promotes the immediate efforts to develop high-valuable hardwood resources in afforestation.However,the shortage of precious timber seeds and seedlings with a few available precious timber tree species hindered the development of precious timber afforestation.It is urgent to collect seeds and cultivate seedlings of high-quality hardwood native tree species in local zone to meet up the urgent demand of seeds and seedlings with high-quality precious timber for afforestation.Quercus chungii F.P.Metcalf.,belonging to genus of Cyclobalanopsis in Fagaceae family,is one of the main constructive species of evergreen broad-leaved forest in subtropical regions of South China,and is also a native tree species with high-quality hardwood.The Q.chungii is an excellent precious timber tree species with outstanding decorative appearance in special technical properties harbored with the straight trunk,high wood density,hardness,high wear resistance,and corrosion resistance.Its heartwood and sapwood are reddish brown with beautiful wood grain,which has always ranked first among the precious timbers of Quercus in China.Its cultivation and utilization prospects are broad.Most tree species in Fagaceae family are symbiotic hosts of Ectomycorrhizal Fungi(ECMF).Therefore,it is of great significance to cultivate mycorrhizal seedlings of Q.chungii for the development,expanding and utilization of Q.chungii,as well as the improvements of physiological and ecological response to stress.In this paper,three kinds of ECMF(Scleroderma sp 1(LY17),Scleroderma citrinum(LY-20),and Scleroderma sp 2(MB))were selected to inoculate with the seedlings of Q.chungii.The mycorrhizal infection rate and root activity were measured and the difference in the seeding growth,photosynthetic physiology and osmotic adjustment substance content of Q.chungii seedlings under different levels of drought stress were compared.Then the dominant symbiotic strains of Q.chungii were obtained.A technology system on the construction of mycorrhizal seedling and evaluation on the effects of mycorrhizal symbiosis to drought resistance of Q.chungii was established,which provided a research foundation and key technical support for the development and utilization of high-quality hardwood tree species of Q.chungii in afforestation.The main findings are following:1)The difference on the infection rate and root activity with different ECMF strains on the Q.chungii roots were significant(P<0.05).ECMF inoculation could promote the growth of Q.chungii seedlings,the MB was the dominant symbiotic mycorrhizal fungi for Q.chungii among the used three strains.Under the condition of normal water supply,the infection rates of three kinds of ECMF on Q.chungii were ranged from 45.67%to 77.00%,in which the highest infection rate(77.00%)was observed in MB with the strongest root activity(0.49 μTFF·g-1·h-1)and obvious yellow and white hyphae and sleeves on the roots.The lowest infection rate(45.67%)was observed in LY-17 with a lower root activity(0.34μTFF·g-1·h-1);After 90 days of inoculation,the height and ground diameter of the seedlings inoculated with MB were 29.41%and 17.54%,respectively,which were higher than those of the control treatments,respectively.The difference on the contents of N,P,and K in the aboveground and underground parts of inoculated plants with ECMF were significant(P<0.05),comparing to those of the controls.The difference on the N content in the aboveground part was significant among different strains(P<0.05),while there was no significant difference(P>0.05)on the P and K contents in the aboveground part and on the N,P and K contents in the underground part among different strains.A higher and better measured root parameters of Q.chungii seedlings inoculated with different ECMF was observed,compared to those of the control treatments.There was significant difference on the measured root values among different strains(P<0.05),and the highest values of root parameters measured were observed in the treatment of MB inoculated seedlings.Comparing with the uninoculated seedlings of controls,an increased measured values on the root length,root surface area,root tip number,branch number and bifurcation number were observed with 62.52%,33.78%,56.42%,53.66%and 67.22%,respectively.The ranking of the evaluation results of the mycorrhizal effect of three ECMFs on Q.chungii was following:MB>LY-20>LY-17.2)Under different drought stress levels(NW(75%-85%of field capacity),CK,MD(55%-65%),and SD(35%-45%)),the Q.chungii seedlings were inoculated with ECMF.After 90 days of inoculation with ECMF,compared with non-inoculated ECMF(NW-CK)treatment,the treatments with inoculated ECMF would promote the growth and development of Q.chungii seedlings,and mycorrhizal symbiotic seedlings would more effectively resist to drought stress.Among them,inoculated MB mycorrhizal dependence and mycorrhizal benefits are significant.Under MD and SD water drought stress,compared with NW water condition(NW-CK),the root infection rate of Q.chungii seedlings inoculated with different ECMF were decreased by 18.42%-40.15%,and the seedling height,ground diameter,and biomass also were decreased by 5.62%-26.36%,5.29%-21.57%,9.49%-63.63%,respectively.Under MD and SD drought stress conditions,the root infection rate of MB inoculation was still the highest(62.33%),and the root activity was the highest(0.39 μTFF·g-1·h-1).At the same time,the seedling height,ground diameter,and biomass of different ECM inoculation treatments increased by 19.58%-17.79%,4.12%-12.75%,and 15.44%-108.95%,respectively,compared with NW-CK under drought stress.The results of photosynthetic physiological characteristics also showed that the net photosynthetic rate(Pn),transpiration rate(Tr),and stomatal conductance(Gs)were decreased gradually with the increase levels of drought stress.Under MD and SD water drought stress,the Pn,Tr and Gs of Q.chungii inoculated with different ECMF were decreased by 3.64%-37.82%,9.74%70.64%,and 13.37%-72.68%,respectively,compared with NW-CK water conditions.The chlorophyll fluorescence parameters(Fm,Fv/Fm,Y(Ⅱ),qP,ETR)and chlorophyll content(total chlorophyll,carotenoid,chlorophyll a and chlorophyll b)of Q.chungii inoculated with ECMF were significantly higher than those of the uninoculated treatments.3)Under different drought stress treatments,when the drought duration was 45 days,the effects of mycorrhizal benefits of ECMF inoculation gradually increased.The contents of soluble sugar,soluble protein,superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),MDA,and free proline in Q.chungii seedlings reached the peak at 90 days.The three ECMFs promoted the accumulation of soluble sugar 2.42%-31.08%and soluble protein 1.57%-46.74%,increased the activity of SOD enzyme 2.11%-145.10%,POD enzyme 10.70%-126.40%,CAT enzyme 7.35%-193.74%,and reduced the content of MDA and free proline.There was no significant difference between LY-17 and NW-CK(P>0.05).Under MD and SD water drought stress,compared with NW-CK under the same stress conditions,the SOD,POD,and CAT of the seedlings inoculated with MB increased by 74.19%-120.76%,88.11%-96.56%,and 124.19%-191.39%,respectively.Inoculation of MB promoted the synthesis of osmotic adjustment substances and antioxidant enzymes in response to drought stress.With the increase of drought degree and the extension of drought duration,the mycorrhizal benefits of three ECMFs gradually increased significantly,among which MB had the best response to drought stress. |
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