| With the development of urban construction,herbaceous flowers are more and more widely used in urban greening because of their various kinds,gorgeous colors and strong resistance.Xi ’an is located in the northwest of China,the low temperature in autumn and winter causes many herbaceous flowers can not survive in the open field.Therefore,there are fewer kinds of herbaceous flowers applied in urban greening in autumn and winter,and the landscape is monotonous.Evaluation and screening of herbaceous flowers with good cold resistance is of great significance to enrich Xi ’an autumn and winter landscape.This study investigated the species,frequency and application status of herbaceous flowers in urban greening in Xi ’an in autumn and winter,analyzed the existing problems in the application of herbaceous flowers and put forward suggestions.A comprehensive evaluation system suitable for Xi ’an autumn and winter herbaceous flowers was established by analytic hierarchy process.81 kinds of introduced autumn and winter herbaceous flowers were evaluated and graded,and 10 kinds of herbaceous flowers with the highest comprehensive evaluation grade were selected for natural low temperature stress and artificial low temperature stress,and their cold resistance was evaluated by measuring the changes of physiological indexes.The main research results are as follows:(1)Through field investigation,it is found that the application forms of herbaceous flowers in urban greening in autumn and winter in Xi ’an mainly include ground cover,flower bed,flower landscape,flowers,flower platform and so on.There were 61 kinds of herbaceous flowers in the survey,among which ophiopogon,Begonia semperflorens and Salvia splendens were more frequently used,which was more than 60%,Most of the herbaceous flowers were not widely used.(2)A comprehensive evaluation system of autumn and winter herbaceous flowers in Xi’an was established by analytic hierarchy process.81 kinds of introduced herbaceous flowers were divided into four grades by applying the evaluation system,among which 10 were grade I,which showed excellent performance in autumn and winter urban greening in Xi ’an and were worthy of extensive promotion and application.(3)After 30 days of natural low temperature stress,the physiological indexes of cold resistance of 10 kinds of herbaceous flowers were measured before and after low temperature stress.It was found that MDA content,proline content and SOD activity of 10 kinds of herb flowers increased.The contents of relative conductivity,soluble protein and POD increased overall,but decreased in a few herbaceous flowers.The relative water content and chlorophyll content showed a downward trend,but a few herbaceous flowers showed an upward trend.(4)Ten herbaceous flowers were treated with four temperature gradients of 5℃,0℃,-5℃ and-10℃ for 36 h and the changes of their physiological indexes of cold resistance were measured.With the decrease of temperature,the relative electrical conductivity of 10 kinds of herbaceous flowers basically increased.The semi-lethal temperature was between-0.84℃ and-5.83℃ according to the fitting Logistic regression equation.The relative water content and chlorophyll content decreased.MDA content,soluble protein content,proline content,POD activity and SOD activity basically increased first and then decreased,but the increasing range and inflection point temperature were different among herbs and flowers.(5)Principal component analysis and membership function method were used to comprehensively evaluate the cold resistance of 10 kinds of herbaceous flowers,and the order from strong to weak was as follows: Brassica oleracea var.acephala ‘Thrush’ >Brassica oleracea var.acephala ‘Xuehuamei’ > coreopsis ‘Solana golden cup’ > Brassica oleracea var.acephala ‘f.tricolor’ > Heuchera micrantha ‘Peach georgia’ > Heuchera micrantha ‘Peach flame’ > Dianthus chinensis ‘Diana’ > Dianthus chinensis‘Chaojibinggao’ > Dianthus chinensis ‘Pili’ > Viola cornuta ‘Xiaomifeng’. |
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