The Physiological And Photosynthetic Response Of Seven Shrub Species To Drought Stress In Guangdong Province

Plant selection for the drought stress plants are significant in the urban greening and urban sustainable development research in modern urbanization.Schefflera odorata cv.Variegata,Ixora chinensis,Gardenia jasminoides,Ervatamia divaricata,Allemanda cathartica,Excoecaria cochinchinensis and Rhododendron pulchrum are common plant species used for urban greening in Guangdong province.In this study,we investigated the physiological and biochemical indexes,photosynthetic indexes and the chlorophyll fluorescence parameters of the seven seedlings under drought stress(0 d,4 d,8 d,12 d)and rehydration(4 d).The drought resistance of these seedlings was evaluated by principal component analysis and factor analysis.(1)With the prolongation of drought stress,the leaf water content of these seedlings decreased,and increased after rehydration.S.odorata,R.pulchrum,I.chinensis and E.cochinchinensis among seven seedlings returned to the controls level.The chlorophyll content of these seedlings increased gradually,and A.cathartica,E.divaricata and E.cochinchinensis returned to the same status as the controls after rehydration.The membrane permeability of these seedlings increased gradually with increasing stress and prolonging duration.After rehydration,the data of A.cathartica and I.chinensis was significantly higher than that of the control,while the remaining seedlings returned to the same status as the controls.The proline content of R.pulchrum increased firstly and then decreased,while the data of other seedlings gradually raised.After rehydration,soluble protein content of R.pulchrum and E.divaricata restored to the status of the controls,while the other seedlings were still significant higher than that of the control.The contents of soluble protein of seven seedlings increased gradually,and G.jasminoides,R.pulchrum and E.divaricata among of them restored to the level of the controls after rehydration.The soluble sugar content increased gradually,and most species restore to the status of the controls except S.odorata.The superoxide dismutase(SOD)activity increased during drought stress period and decreased after rehydration,G.jasminoides,E.divaricata and E.cochinchinensis among of these species returned to the same status as the controls.The content of malondialdehyde(MDA)increased gradually,and after rehydration I.chinensis restore to the status of the controls,while the other seedlings still significant higher than that of the control.(2)The photosynthetic responses of S.odorata,I.chinensis,G.jasminoides,E.divaricata,A.cathartica and E.cochinchinensis were investigated under drought stress.Their net photosynthetic rate(P_n),stomatal conductance(G_s)and transpiration rate(T_r)reduced or significantly reduced under drought stress treatment and increased after rehydration.Their C_i of decreased under drought stress,other seedlings increased after rehydration except A.cathartica.Their stomatal limitation(L_s)increased during drought stress period and decreased after rehydration,E.divaricata returned to the same status as the controls.(3)With the prolongation of drought stress,the excitation capture efficiency of PS?(F_v'/F_m')in seven shrub seedlings gradually decreased.I.chinensis,E.cochinchinensis and R.pulchrum recovered to the control level after rehydration,while the other seedlings were still significantly lower than that of the control.The active quantum efficiency of PSII(Y(II))of seven shrubs gradually decreased.R.pulchrum and S.odorata recovered to the control level after rehydration,while the others were still significant lower than that of the control.The electron transport rate(ETR)of seven seedlings decreased with increasing stress intensity and increased after rehydration.S.odorata and E.divaricata among of them returned to the same status as the controls.Photochemical quenching(qP)continued to decrease with the increase of stress intensity and S.odorata recovered to some status of the control.The non-photochemical quenching(NPQ)of seedlings increase continually and returned to the control level after rewatering except G.jasminoides.(4)Using the principal component analysis to study the physiological indicators and chlorophyll fluorescence parameters of seven shrubs,the results showed that the order of drought resistance of seven shrub seedlings rated from high to low was:R.pulchrum>S.odorata cv.Variegata>E.cochinchinensis>G.jasminoides>I.chinensis>E.divaricata>A.cathartica.(5)The photosynthetic characteristics of the six shrub seedlings were evaluated with principal component analysis,indicating that the order of drought resistance was S.odorata cv.Variegata>E.cochinchinensis>E.divaricata>G.jasminoides>A.cathartica>I.chinensis.