Physiological Responses Of Five Woody Species To Saline And Alkali Stress And The Alleviation By Exogenous Substances

In this paper,the responses of seedlings of Ulmus pumila,Lycium dasystemum.Celastrus orbiculatus,Syringa microphylla and Pinus sylvestris var.mongolica under NaHCO₃ stress and the effects of trehalose,spermine,spermidine,choline chloride and ascorbic acid on saline and alkaline stress tolerance of the above woody plants were studied.Through this program,the relationship of the physiological index determined in this reserch and saline and alkaline stress tolerance and the reliability of these indices as saline and alkaline tolerance selection criteria was analysed and discussed,at the same time.the tolerance scopes of woody plants refered in this research against saline and alkaline stress and the effets of exogenous substances on saline and alkaline tolerance were tested and discussed for the purpose of providing theoretical basis and technique reference for chosing salt-tolerant trees,improving salt tolerance of plants as well as afforesting and gardening successfully and effectively in Daqing saline and alkaline area.The main results were as follows:(1) With the increasing stress intensity,the dry weight increments of roots,shoots and leaves of seedlings of the five woody species expressed decresing trends as well as total biomass increments,but different species had different decresing scales.The order in decreasing scale of biomass increment of the five species followed P.sylvestris var.mongolica> S.microphylla>C. orbiculatus>U.pumila>L.dasystemum.As far as decreasing scale of biomass increment of different part of different species.U.pumila.S.microphylla and P.sylvestris var.mongolica followed leaf>root>stem;L.barbarum followed leaf>stem>root;and C.orbiculatus followed root>leaf>stem.Under different NaHCO₃ stress intensity,the root/shoot ratio of U.pumila and L. barbarum rose continuously;the ratio of C.orbiculatus under mild NaHCO₃ stress declined,and then increased;the ratio of P.sylvestris var.mongolica under mild NaHCO₃ stress increased. and then declined:the ratio of S.microphvlla changed slightly.The saline and alkaline stress tolerance of the five woody species followed L. dasystemum>U.pumila>C,orbiculatus> S.microphylla>P,sylvestris var.mongolica.(2) Under saline and alkaline stress,chlorophyll contents in the leaves of woody plants with different life forms decreased identically.At any stress stage,with the increasing stress intensity,chl.a.carotenoid contents and chl.a/b did not express identical trends.Under longtime stress stage,total chlorophyll and chl.a contents had identical trends.Chlorophyll content was not a reliable indicator for appraising salt tolerance of woody plants belonging to different living forms,because the tolerance rank judged by chlorophyll content followed L. dasystemum>C.orbiculatus>U,pumila> S.microphylla>P,sylvestris var.mongolica.But the tolerance rank of these plants should follow L.dasystemum>U.pumila>C.orbiculatus>P. sylvestris var.mongolica.These woody plants belonging to different living responsed identically to NaHCO₃ stress. that is,net photosynthetic rate,transpiration rate and stomatal conductance all declined obviously.According to the changes of photosynthesis parameters of the five seedlings,it was concluded that under lower stress intensity,the main factor leading to decreasing in photosynthesis rate of U.pumila and L.dasystemum was stomatal lilnitation,while nonstomatal limitation under higher stress intensity.The main factor leading to decreasing in photosynthesis rate of C.orbiculatus and P.sylvestris var.mongolica was stomatal limitation. Non-stomatal limitation was the main factor leading to decreasing in photosynthesis rate of S. microphylla.Photosynthesis rate could be a reliable indicator for appraising salt tolerance of woody plants with different life forms,because the tolerance rank judged by chlorophyll content followed L.dasystemum>U,pumila>C,orbiculatus> S.microphylla>P.sylvestris var. mongolica,which was identical with their salt tolerance degrees.Under saline and alkaline stress,Fm,Fv,Fv/Fm,ΦPSâ…¡of the five seedlings deceased gradually with the increasing stress intensity.Fo and NPQ,however,expressed increasing trends.Fo,Fv and Fv/Fm could serve as an effective index for salt tolerance assessment of woody plants with different life forms,while Fm,NPQ andΦ_PSII could not.(3) For any indicator of proline,soluble sugar and soluble protein,the five woody plants with different life forms had identical trends.Proline content was not a reliable indicator for appraising salt tolerance of woody plants with different life forms,because salt-tolerant L.dasystemum and U.pumila had a less increasing scale of proline than non-salt-tolerant U.pumila and L.dasystemum,while salttolerant U.pumila and C.orbiculatus had a larger increasing scale of proline than non-salttolerant S.microphylla.Soluble sugar and soluble protein content could not served as a reliable indicator for appraising salt tolerance of woody,plants with different life forms,too.Shoot Na⁺ content could be an effective indicator for salt tolerance assessment of woody plants with different life forms.But glycophyte and halophyte had different relationship of shoot Na⁺ content and salt tolerance.For glycophyte the relationship was negative,while it was positive for halophyte.Shoot Na⁺/K⁺ was not a good selction criterion.(4) SOD,CAT and GR could serve as a reliable indicator for appraising salt tolerance of woody plants with different life forms,and SOD and CAT were more effective.POD,APX,AsA and GSH were not reliable selction criteria.Increase in POD activity did not seem to be a tolerance component,but a stress symptom.(5) The production rate of O₂^-,H₂O₂ and MDA contents and electrolyte leakage in leaves of Celastrus ofbiculatus seedlings treated with exogenous trehalose under NaHCO₃ stress decreased significantly(P<0.05),while the activities of SOD,CAT,POD,APX,GR.and the contents of ASC and GSH increased obviously.Significant decreases in the production of reactive oxygen species(O₂^- and H₂O₂).MDA content as well as electrolyte leakage in leaves were observed with Spd and Spm treatments(P<0.05).The results showed that Spd application increased the activities of SOD, CAT.POD and APX as well as the contents of GSH,CAR and Pro in leaves of stressed plants. but had no obvious effect on AsA content.Under NaHCO₃ stress,Spin spraying also increased the activities of POD and APX as well as the contents of GSH,CAR and Pro,but had no effect on SOD and AsA.Unexpectedly,it caused a obviously decrease in the activity of CAT.ASA treatment could inhibit the decrease in the activities of CAT,APX,GR,increase SOD activity and ASA content,and prohibit the increase in H₂O₂ and MDA content and electrolyte leakage.But it prohibited the increase in GSH content.Exogenous choline chloride could not effectively inhibit the increase in H₂O₂ content and electrolyte leakage.In addition,it enhanced the increase in MDA content.Choline chloride treatment prohibited the increase in APX and enhanced the decrease in CAT.It also could not effectively increase the activity of SOD.