| Salt stress is one of the main environmental stresses faced by land plants,and most vascular plants can improve their survival ability under such adverse conditions as salt stress by forming mycorrhizal symbionts with soil fungi.There are many species of Quercus in the Fagaceae family and Quercus plants are typically ectomycorrhizal trees with strong adaptability.In this study,three Quercus species(Q.acutissima,Q.dentata and Q.variabilis)common in warm temperate regions were selected to conduct a greenhouse pot experiment.Two inoculation levels were set by inoculation with the ectomycorrhizal fungus Laccaria bicolor,the inoculation group and the control group.Then NaCl solution was added to set three salt stress levels,including control with no salt stress(0%NaCl),low salt stress(0.4%NaCl)and high salt stress(0.8%NaCl).We compared the seedling growth and physiological characteristics of three Quercus species under different salt stress conditions,and explored the effect of ectomycorrhizal fungus on the tolerance of Quercus plants to salt stress conditions.The main results are as follows:Salt stress had adverse effects on growth of three Quercus seedlings.Under salt stress.chlorophyll content,net photosynthetic rate,transpiration rate,instantaneous water use efficiency.stomatal conductance and chlorophyll fluorescence parameters of three Quercus seedlings showed a decreasing trend.The growth of plant height and basal diameter was inhibited,biomass and leaf water content were decreased,and leaves showed salt damage symptoms such as burnt leaf macula.The inhibition effect was more obvious with the increase of soil salt content.Under high salt stress,seedling leaves gradually dried up and fell off.There were significant differences in seedling growth ability and responses to salt stress among three Quercus species.In terms of growth performance,plant height,basal diameter,root,stem and leaf biomass and total biomass of Q.acutissima seedlings were significantly higher than those of Q.dentata and Q.variabilis under no salt stress condition.From physiological characteristics,net photosynthetic rate,transpiration rate,stomatal conductance.instantaneous water use efficiency and chlorophyll content of three Quercus seedlings had little difference,but root,stem and leaf nitrogen content of Q.acutissima seedlings were significantly higher than those of Q.dentata and Q.variabilis.Under low salt stress,leaf biomass and total chlorophyll content of Q.variabilis seedlings did not decrease significantly,but those of Q.acutissima and Q.dentata significantly decreased.Under high salt stress,basal diameter,root to shoot ratio and total chlorophyll content of Q.variabilis seedlings did not decrease significantly.but those of Q.acutissima and Q.dentata significantly decreased.According to the comprehensive evaluation value of salt tolerance of three Quercus species obtained by principal component analysis combined with membership function method,the salt tolerance of three Quercus plants was as follows:Q.variabilis>Q.acutissima>Q.dentata.The influence of ectomycorrhizal fungi on Quercus plants is related to plant species and the symbiotic environment.Among three Quercus species,only Q.dentata formed a good symbiotic relationship with L.bicolor.Under no salt stress,L.bicolor inoculation significantly increased leaf nitrogen content,root biomass,total biomass and root to shoot ratio of Q.dentata seedlings,and promoted seedling growth.Under low salt stress,L.bicolor inoculation significantly increased root biomass,specific leaf area.chlorophyll a content and total chlorophyll content,and leaf K+content,and significantly decreased leaf Na+ content of Q.dentata seedlings,which alleviated negative effects of salt stress on plants.Under high salt stress,L.bicolor inoculation significantly decreased leaf water content,electron transport rate and actual quantum yield of photosystem I,photochemical quenching and maximum quantum yield of photosystem II of Q.dentata seedlings,which aggravated negative effects of salt stress on plant physiology.This study compared response differences to salt stress and the salt tolerance of three Quercus species in warm temperate zones,and explored growth promoting effects of ectomycorrhizal fungi on Quercus plants.The results enriched the theory of growth promoting effects of ectomycorrhizal fungi on Quercus plants.and provided a theoretical reference for the selection and management of Quercus species for vegetation restoration in saline-alkali areas. |
