Effects Of Drought And Salt Stresses On Photosynthetic Characteristics Of The Four Greening Species

In order to study the effects of adversity on the photosynthetic characteristics of greening tree species in northwest China,select the excellent plant resources and establish a reasonable index system of adversity-resistance in this area,the four greening tree species Lespedeza bicolor,Prunus besseyi,Hippophae rhamnoides and Shepherdia argentea in the region were selected as the research objects,two groups of environmental stresses were simulated,namely drought stress(W1,W2,W3,which indicated that the watering volume were 30%-35%,40%-45%,50%-55%of the field capacity,respectively)and salt stress(S1,S2,S3,which indicated that NaCl concentration were 3‰,5‰,8‰,respectively).The differences of photosynthetic gas parameters P_n(net photosynthetic rate),T_r(transpiration rate),G_s(stomatal conductance)and C_i(intercellular CO₂concentration)under different stresses and those of different species under the same stress were compared.The energy absorption,transmission,distribution and transformation of each species under stresses were investigated by comparing the fast chlorophyll fluorescence induction kinetic parameters(JIP-test parameters).Based on the above results,the dominant greening species was selected.The grey correlation analysis was used to calculate the correlation degrees between part of above-mentioned index parameters and the leaf biomass of the four species.Screening indicators with strong indication by ranking degrees of correlation.The main findings are as follows:(1)Photosynthetic gas parameters P_n,T_rand G_sof L.bicolor and S.argentea showed a decreasing trend with the enhancing of drought and salt stresses,those of P.besseyi were more sensitive to salt stress than drought stress.However,P_n,T_rand G_s of H.rhamnoides had no significantly difference under both stresses.H.rhamnoides showed stable resistance.(2)Under different degrees of drought and salt stresses,P_nand T_rof H.rhamnoides were significantly higher than those of three other species.This may be related to the physiological structure of H.rhamnoides,which is different from three other species.(3)The light absorption index(PI_abs)and PSII maximum photochemical efficiency(F_v/F_m)of H.rhamnoides were remarkably higher than those of three other species.Most of the specific activity parameters of H.rhamnoides were significantly lower than three other species.This is determined by the energy allocation strategy of H.rhamnoides under different adversity conditions.It is an important part of its survival strategy.(4)The results of calculating and ranking by grey correlation analysis showed that the degree of correlation between JIP-test parameters and the leaf biomass of each species was higher.The transient changes of chlorophyll fluorescence were faster and more sensitive than the changes of photosynthetic gas under different environmental stresses.In conclusion,photosynthetic gas parameters can directly reflect the response of plant photosynthetic process to different environmental stresses,which is the apparent embodiment of the variation of photosynthesis intensity.The JIP-test parameters can specifically reflect the energy absorption,transmission and transformation of plant in the process of photosynthesis,which is the internal mechanism driving the response of plant photosynthetic process.The results of the experiment indicated that H.rhamnoides had stable responses to stresses because it had more suitable physiological structure and stronger adaptability.From the results of grey correlation analysis,for most of species in the experiment,the JIP-test parameters were more sensitive to the environmental stresses.Paying attention to the transient changes of chlorophyll fluorescence is an important part of studying the survival and growth of plants in adversity.