Study On Cold Tolerance Mechanism Of Five Evergreen Broad-leaved Species As Temperature Fell

In the thesis, the cold tolerance abilities of five tree species introduced were studied through the determination of chlorophyll fluorescence characteristics and physiological index. The main results have been described as follows:1 All species showed some cold tolerance ability under early low temperature stress. The malondialdehyde (MDA) contents and relative electric conductivity rate (RECR) of all species ascended obviously, which indicated that more lipid peroxidations occurred in the process of temperature decreasing. The soluble sugar, proline and the activity of peroxidase (POD) of 5 species ascended, which reduced the damages of low temperature stress at some degree.2 All species were damaged badly after continuous low temperature. From January to February, 2008, the leaf morphologic characteristics of all species but llex latifolia Thunb changed remarkably. Some leaves faded as well as fell off. All species'contents of MDA and RECR ascended but their contents of soluble sugar, proline and the activity of peroxidase (POD) descended. Trees were damaged severely.3 The chlorofluorescence kinetic parameters of five evergreen broad-leaved species changed remarkably as temperature decreased. From November, 2007 to February, 2008,the photosystem II maximal photochemical efficiency(Fv/Fm) , the photochemical quenching (qP) and PS II actual Photochemical efficiency(ΦPS II) descended, which meant that the ability of PS II descended in the process of temperature decreasing. The non-photochemical quenching (qN) of all species ascended remarkably, which protected the PSII by qN pathway at some degree. All chlorophyll fluorescence induction kinetic parameters showed that PS IIs of 5 species were damaged in the process of temperature decreasing.4 The cold tolerance abilities of 5 species could be ranked as: llex latifolia Thunb. > MangLietia Yuyuanensis Law > Michelia fulgens Dandy > Michelia platypetala>M.maudiae Dunn.