| Fraxinus chinensis Roxb is a deciduous tree of the Oleaceae family and Fraxinus genus.The tree has a long history of cultivation in China and has the characteristics of beautiful tree body,high posture,long green period,fast growth speed,convenient management and so on.It is used as a street tree.Due to frequent occurrence of extreme weather under climate change,low temperature and frost often occur in late autumn or early spring.This climate has a great influence on the normal growth of ornamental trees.In this experiment,two year old Fraxinus chinensis Roxb tree was selected as the research materials.The electrical impedance spectroscopy(EIS)parameters and electrolyte leakage(EL)were used to determine the cold resistance of the stems and leaves for different simulated frost and frost duration.At the same time,under the corresponding low temperature conditions,the content of soluble protein,the activity of superoxide dismutase(SOD)enzyme,the activity of peroxidase(POD)enzyme,the content of malondialdehyde(MDA),the content of proline,the content of dry matter,etc.were measured to determine the low temperature range of the physiological activity under frost stress,and to find the best physiological indexes and EIS parameters suitable for the estimation of the cold resistance of Fraxinus chinensis Roxb.The research results will provide a new reference method for rapid and non-destructive detection of cold resistance for ornamental trees and have guiding significance for preventing and mitigating the disasters caused by frost under climate change.The main results are as follows:1.In late autumn in November,the highest cold resistance of leaves and stems of Fraxinus chinensis Roxb were-19.58°C and-27.90°C respectively.In early spring in March,the highest cold resistance of stem of Fraxinus chinensis Roxb was-35.08°C.In late autumn in November,once the temperature was lower than-5°C for more than 24hours,or the temperature was lower than-10°C with duration of over 6 hours;in early spring in March when the temperature was below-10°C for more than 12 hours,or the temperature was-15°C with duration of over 6 hours,the corresponding protection measures should be taken to avoid frost disaster caused by the frost temperatures.2.The EIS of the stems and leaves of the Fraxinus chinensis Roxb showed a single arc during the simulated frost temperature treatment,and the cold resistance enhanced the radian of the EIS,which could be used as a qualitative index to judge the cold resistance of the Fraxinus chinensis Roxb.3.The EIS parameters extracellular resistance r_e,intracellular resistance r_i,relaxation timeτand distribution coefficient of relaxation timeψcould be used to estimate the cold resistance of the stems.The correlation coefficients were 0.839,0.936,0.887 and 0.815respectively.The r_e and r_i could be used to estimate the cold resistance of the leaves with the correlation coefficients of 0.965 and 0.535 respectively.4.The content of soluble protein,SOD enzyme,MDA content,proline content and dry matter content might be used to estimate the cold resistance of the leaves of Fraxinus chinensis Roxb,and among these indexes the contents of soluble protein,MDA and dry matter significantly related to the cold resistance of the leaves.The correlation coefficients were 0.876,-0.922 and 0.934 respectively.The content of soluble protein,SOD enzyme activity,POD enzyme activity and proline content might be used to estimate the cold resistance of the stems,in which the activities of SOD and POD enzyme were significantly positively correlated with the cold resistance of the stems with the correlation coefficients of 0.974 and 0.942 respectively.5.The contents of mineral elements such as N,P,K,Ca and Mg in leaves of Fraxinus chinensis Roxb treated by simulated frost did not change significantly. |
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