Physiological Response And Evaluation Of Drought Resistance Of Three Common Greening Plants On Highway Side Slope To Drought

The rapid development of economy has greatly promoted the highway construction in our country,and the highway construction not only increases the speed,but also causes the greening problems such as soil erosion and structural instability of highway side slope.Due to the lack of soil nutrients,poor water storage capacity and difficult maintenance in the later stage,the growth status of the highway side slope plants is poor and the survival rate is low.Therefore,the selection of plants with good stress resistance is of great significance to improve the effect of the slope greening.In this study,Festuca elata,Trifolium repens and Cynodon dactylon,which are commonly used in the highway side slope greening,were selected.This experiment was conducted in the Wuhan Botanical Garden of the Chinese Academy of Sciences from July to December 2020 to simulate different drought stress and rehydration environmental gradients(blank（CK,95%of field moisture capacity）,light drought（LD,75%of field moisture capacity）,severe drought（SD,55%of field moisture capacity）,light drought-rehydration（LDW,95%of field moisture capacity）and severe drought-rehydration（SDW,95%of field moisture capacity）.The response characteristics of growth,physiological,biochemical and photosynthetic characteristics of the slope plants to drought-rehydration were studied,and their drought resistance was comprehensively evaluated by multi-index,in order to provide some reference and theoretical basis for the selection of the highway side slope greening plants in China.The main results are as follows:（1）Effect of drought-rehydration on the growth of highway side slope greening plants.Drought inhibited the growth of Festuca elata,Trifolium repens and Cynodon dactylon.With the aggravation of drought stress,the biomass of all parts of the plant decreased,and only the underground biomass of Cynodon dactylon increased,that is,the root top ratio were increased,indicating that it has a strong ability to resist drought.After rehydration,the biomass of each part of the three tested plants changed differently,the plants showed a certain ability to repair after drought,but when the stress damage was too serious,the damage could not be repaired after rehydration.The recovery effect of rehydration on plant growth will show a lag effect.（2）Effects of drought-rehydration on biochemical characteristics of highway side slope greening plants.Under drought stress,the contents of proline,soluble protein and soluble sugar in Festuca elata and Trifolium repens were increased.Drought inhibited protein synthesis in Cynodon dactylon and accelerate protein degradation,resulting in an increase in proline content and a decrease in soluble sugar content.After rehydration,the soluble protein of the tested plants returned to the control level.The three substances are effective osmotic regulators,the tested plants can reduce the injury of drought stress through osmotic regulation.Drought caused membrane lipid peroxidation of Festuca elata and Trifolium repens,but them could repair themselves after rehydration.The cell membrane lipid of Cynodon dactylon was not affected by drought stress and showed good drought resistance.Drought stress caused the accumulation of reactive oxygen free radicals and hydrogen peroxide in three tested plants.After rehydration,the repair of each index was different,showing a certain compensation and lag effect.The three tested plants all use enzymatic and non-enzymatic reaction systems to reduce the toxic effects of reactive oxygen species and peroxides,but the application strength and repair condition are different.（3）Effects of drought stress and rehydration on photosynthetic physiological characteristics of highway side slope greening plants.Under drought stress,only the chlorophyll content of Cynodon dactylon in light drought treatment group increased.After rehydration,the chlorophyll content of Festuca elata decreased.Drought inhibited the synthesis of chlorophyll and damaged the photosynthetic pigment structure of Festuca elata,which could not be repaired after rehydration.Moderate drought was beneficial to Cynodon dactylon,and the synthesis of chlorophyll showed compensation effect after rehydration.The photosynthetic rate（P_n）and conductance to H₂O（G_s）of the three tested plants had the same trend,and the net photosynthetic rate of Festuca elata,Trifolium repens and Cynodon dactylon may be mainly affected by stomatal limiting factors.Under drought stress,the non-photochemical fluorescence quenching coefficient（NPQ）of the three plants increased at first and then decreased,while the photochemical efficiency（Fv/Fm）,photochemical fluorescence quenching coefficient（q P）and electron transfer rate（ETR）of Festuca elata and Trifolium repens decreased,while Cynodon dactylon was on the contrary.After rehydration,only the Fv/Fm and ETR of Festuca elata decreased,showing that both Festuca elata and Trifolium repens were inhibited by photoinhibition.Cynodon dactylon showed strong drought resistance and repair ability after drought.（4）Comprehensive evaluation of drought resistance.According to the combination of principal component analysis and membership function,the D values of Festuca elata,Trifolium repens and Cynodon dactylon,were 0.327,0.257 and 0.401.According to the D value,the drought resistance of Cynodon dactylon was the strongest,Festuca elata was followed,Trifolium repens was the weakest.