Comprehensive Evaluation Of Physiological Response And Salt Tolerance Of Chrysanthemum Morifolium Under Salt Stress

With the increasingly serious problem of soil salinization,the sustainable development of modern agriculture is seriously restricted.Exploring the salt tolerance mechanism of plants and breeding salt-tolerant plants are effective ways to improve and apply saline-alkali land.As a perennial herb,Chrysanthemum morifolium has a broad application prospect in landscape greening in cold regions because of its good adaptability and appreciation.In order to explore the physiological response of ground cover chrysanthemum under salt stress and select and breed the varieties with strong salt tolerance,the cuttage seedlings of four lines of ground cover chrysanthemum(’C17-141’,’C17-11’,’C17-KH2’,’C17-118’)were used as experimental materials.To simulate different concentrations of salt stress(0,100 mmol/L,200 mmol/L and 300 mmol/L Na Cl),the leaf growth indexes,plasma membrane permeability,antioxidant enzyme activity,osmotic regulatory substances,photosynthetic characteristics and secondary metabolites of ground cover chrysanthemum were measured and analyzed.Correlation analysis,membership function value method and principal component analysis were used to evaluate the salt tolerance,which provided scientific basis for the application of ground cover chrysanthemum in salinized land.The main research results are as follows:(1)Under salt stress,the growth of four ground cover chrysanthemums was inhibited,and the leaves lost water to varying degrees.With the increase of salt concentration,plant height growth,total biomass and relative water content of leaves all showed a downward trend,and the greater the salt concentration,the more significant the decrease was.Under the stress of 100 mmol/LNa Cl,the ground cover chrysanthemum grows well,and only a small part of the leaves with older leaves turn yellow.Under the stress of 200 mmol/L Na Cl,the leaves of four ground cover chrysanthemums were obviously damaged,and about one third of them were scorched.Under the salt concentration of 300mmol/L,the leaves of ground cover chrysanthemum appeared a lot of shedding and yellowing,and the plant height growth and total biomass decreased to the minimum.(2)Under salt stress,the plasma membrane permeability of the four ground cover chrysanthemums changed,and under osmotic stress,the synthesis of osmotic adjustment substances increased.With the increase of salt concentration,the relative conductivity and MDA content showed an upward trend;The proline content of’ C17-141’ and’ C17-11’ increased,while the proline content of’ C17-118’ and’ C17-KH2’ increased first and then decreased.The contents of soluble sugar and soluble protein generally increased first and then decreased.(3)Under salt stress,the active oxygen content of four ground cover chrysanthemums increased in different degrees,and the antioxidant system responded.With the increase of salt concentration,SOD activity generally increased first and then decreased.The POD activities of’C17-141’ and’ C17-118’ generally showed an increasing-decreasing-increasing trend,while those of’C17-11’ and’ C17-KH2’ first increased and then decreased.The cat activities of’ C17-141’ and’ C17-118’ increased first and then decreased,the cat activities of’ C17-11’ decreased-increased-decreased,and the cat activities of’ C17-KH2’ decreased first and then increased.The activity of APX increased first and then decreased.(4)Photosynthesis of four ground cover chrysanthemum seedlings was inhibited to varying degrees under salt stress.Chlorophyll content,Pn,Ci,Gs and Tr in leaves were significantly lower than those in the control.Chlorophyll fluorescence parameters Fv/Fm,ФPSII,q P and ETR all decreased in different degrees,and NPQ showed an overall upward trend.(5)The content of secondary metabolites in leaves of four ground cover chrysanthemum seedlings increased in different degrees under salt stress.With the increase of salt concentration,the total flavonoids content first increased and then decreased.The total polyphenols content of’ C17-141’ and’ C17-11’ increased,while the total polyphenols content of’ C17-118’ and’ C17-KH2’increased first and then decreased.(6)According to the correlation analysis and fuzzy membership function comprehensive evaluation,the order of salt tolerance of the four species was as follows: ’ C17-141 ’ > ’ C17-11 ’ >’ C17-KH2 ’ > ’ C17-118 ’.Two principal components are obtained by principal component analysis,and the index with high load weight in the two principal components can be used as the key identification index for the evaluation of salt tolerance.