Study On Salt Tolerance Of Eight Clones Of 'Zhongshansha' Of Breeding For Genus Taxodium

Taxodium 'Zhongshansha'[(Taxodium distichum×T.mucronatum)×T.mucronatum] which have strong water-resistance and salt-tolerance characteristic,are excellent trees widly used to empoldering salina and meliorating entironment because they can grow well at littoral salina(pH8-8.5,contained salt about 0.1%).Backcross hybrids were got by Taxodium 'Zhongshansha302' and T.mucronatum.Their salt-tolerance and salt-tolerant mechanism are short of study.In this paper,salt tolerance of eight clones(CL) of 'Zhongshansha' were appraised and two different salt-tolerant clones of 'Zhongshansha' were chosen to study the salt-tolerant mechanism by comparing their physiological reaction and ion uptakes and transports in condition of salt stress.Eight clones of 'Zhongshansha' breeding were used for studying their salt tolerance treated by different concentration(3.0,3.5,4.0,4.5,5.0 g·L^-1) of NaC1 in condition of water culture.The relative growth of breeding height(RG),salt indexes and relative electrolytic leakage which were main indexes and the other indexes which were relative growth of stem,dry weight,root shoot ratio,RWC in overground and RWC in root were used to study their salt tolerance.Results indicated that the tested clones were classified into three groups:weak salt tolerance,moderate tolerance and strong tolerance.CL118 had strong salt-tolerance,which salt-tolerance limit was 4.0 g·L^-1～4.5 g·L^-1;CL136,CL1, CL146 and CL149 had moderate tolerance,which salt-tolerance limit was 3.5 g·L^-1～4.0 g·L^-1;CL 102,CL 27 and CL 24 had weak tolerance,which salt-tolerance limit was 3.0 g.L^-1～3.5 g·L^-1.There were exceedingly significant correlation in level of 0.01 between RG and Relative electrolytic leakage or RG and SI,or SI and Relative electrolytic leakage by twos,and three indexes(RG,SI and Relative electrolytic leakage) and five indexes (Relative growth of stem,Dry weight,Root shoot ratio,RWC in overground and RWC in root) had significant correlation.So RG,SI and Relative electrolytic leakage could be used as synthetic identification index for salt tolerance of 'Zhongshansha'. CL 118(with relatively strong salt resistance) and CL 102(with relatively weak salt resistance) were chosen and studied in NaCl stress on physiological reaction.Results indicated that chlorophyll content in leaves decreased at all times.Compared with the control,chlorophyll content was inapparent treated by lower NaC1 concentration(3.0 g·L^-1)but with NaC1 concentration increasing,chlorophyll content degressive extent of CL 118 was much lower than CL 102;CL 118 had stronger ability to clear away free radical treated by lower NaC1 concentration,which SOD activity reached maximum at 3.5 g·L^-1 concentration and was higher than the control.,but its activity observably declined with NaCl concentration increasing.The soluble protein in leave all increased and its amplitude of CL 118 was much lower than CL 102,and the difference between CL 118 and CL 102 was inapparent with NaCI concentration increasing.Relative electrolytic leakage in leave all increased and its amplitude of CL 118 was much lower than CL 102.Pro content in leave ascended as a whole at lower NaCl(3.0g·L^-1-3.5g·L^-1) concentration,that of CL 118 doubly increased,and its amplitude of CL 118 was bigger than CL 102.Pro content in leave of CL 118 ascended at higher NaC1(3.0g·L^-1-3.5g·L^-1) concentration and CL 102 failed.Soluble sugar content in leaf and root of CL 118 enhanced and its amplitude in leave was much higher than in root.Soluble sugar content in leaf and root of CL 102 were declined.CL 118 osmoregulated mainly through increasing of soluble sugar content and pro content.The effects of salt stress on ion uptakes and transports on CL 118 and CL 102 were studied.Results indicated that important reasons for stronger salt resistance of CL 118 were root selectivity absorbency toward K+ and Ca2 of CL 118 in order to restrain Na⁺ coming into root was stronger than that of CL 102,and Na⁺ in leaves of CL 118 accumulation was less than that of CL 102.It showed that root transported much more K⁺,Ca²⁺ and Mg²⁺ to leaves for keeping metabolized active and lower level of Na⁺/K⁺ value in root,stem,and leaf of CL 118.