Physiological Effects Of Different Concentrations Of Chloride Deicing Salt And Freeze-thaw Stress On Secale Cerale L. Seedlings

Chloride deicing salt stress usually coincides with the event of freeze-thaw,the short-term adaptation of Dongmu-70 Secale cerale L.seedlings to these stresses were investigated in this paper.The chloride deicing salt and the freeze-thaw?FT?simulation experiments were carried out in the lab and alternation refrigerator.The changes of soluble sugar,soluble protein,relative conductivity?RC?,malondialdehyde?MDA?and catalase?CAT?activity in seedlings were studied under freeze-thaw stress?10,5,0,-5,0,5 and 10°C?and 0,200,400 and 600 mmol·L^-1 of chloride deicing salt stress?CK,D₁,D₂ and D₃?.The changes of photosynthetic physiological characteristics?assimilation rate?Pn?,transpiration rate?Tr?,internal CO₂ concentration?Ci?,stomatal conductance?Gs?and water use efficiency?WUE??during the recovery phase were studied.The results indicated that the content of RC,MDA,soluble sugar,soluble protein and CAT activity in different treatment groups rose first and then decreased within a freeze-thaw cycle,among the maximums of content of soluble sugar,soluble protein and CAT activity reach the maximum value at 0°C?T₃?were observed,the MDA value peaked at-5°C?T₄?while the RC content reached the maximum value of 29.5%?FT?,30.0%?D₁×FT?,36.8%?D₂×FT?and 32.6%?D₃×FT?,respectively,under the combined stress.Meanwhile,the damage to the seedlings was aggravated with the increase of deicing salt concentration.During the recovery phase?T₈:24 h after freeze-thaw stress and T₉:6 d after freeze-thaw stress?,there was significant difference either in MDA and CAT activity between D₂×FT and D₂ or in RC,MDA,soluble sugar and CAT activity between D₃×FT and D₃.The seedlings showed different adaptability under the different intensity of combined stress,and the sequence of the changes in RC,MDA,soluble sugar,soluble protein and CAT activity can be patterned as D×FT>FT>D?D₃>D₂>D₁?>CK.Pn,Tr,WUE and Gs of seedlings under D,FT and D×FT stress were higher than CK,and Pn,Tr,WUE and Gs increased with the increase of chloride deicing salt concentration,while the change of Ci showed a significant negative correlation with Pn,which indicated that the decrease of Pn in seedling was mainly caused by stomatal factors that caused the assimilation of mesophyll cells in leaves of seedlings.Freeze-thaw and chloride deicing salt complex stress exhibited a synergistic effect on the plant,which indicates that the snow-melting operation would be more harmful in spring and autumn to plants than in winter.