| In recent years, five evergreen broadleaved tree species such as Elaeocarpus glabripetalus Merr, Cinnamomum chkiangense,Parakmeria lotungensis, Manglietia- insignis, and Michelia chepensis Dandy have been introduced and cultivated in Nanjing from other provinces. In this paper, the author has investigated their photosynthetic rates and related cold-resistance indexes in natural decreasing process of air temperature and also analyzed the differences of their cold-resistance among those five tree species by means of subordinate function method. The main results were described as follows:1) With natural decrease of air temperature, the total content of leaf chlorophyll, the content of chlorophyll a, chlorophyll b and the ratio of chlorophyll a to chlorophyll b all varied relevantly. Among them, the content of chlorophyll a showed a larger range than that of chlorophyll b. Meanwhile, the total content of chlorophyll varied with a same trend as photosynthetic rate in 5 species and seemed to present a close positive correlation with the decreasing air temperature.2) With natural decrease of air temperature in different months (from September 2006 to March 2007), the leaf cell membrane of all five tree species were hurt at different levels. Except for Elaeocarpus glabripetalus Merr, the injury caused by low temperature in the first 10 days of March 2007 among other four tree species was more serious than that caused after their experiencing winter coldness exercises. Furthermore, Parakmeria lotungensis was injured most heavily.3) The content of soluble sugars in leaf cells had a close relationship with the cold-resistance of different tree species. Those tree species with stronger cold-resistance could adjust the contents of soluble sugars to adapt the low temperature, so as to reduce the injury to their cell membrane. Their contents of soluble sugars appeared to be highest just before the lowest air temperature came. In contrast, the weaker ones adjusted them passively as the temperature varied and presented a narrow range.4) The activity of leaf POD was sensitive to low air temperature. The species with stronger cold-resistance were more sensitive to low air temperature and changed more steadily as air temperature decreasing than those with weaker cold-resistance. Therefore, increasing the activity of leaf POD could be an important way to make trees to adapt the low temperature. 5) Similar conclusions as other research reports were made that spermidine had an important effect in adapting low temperature and that it was quite sensitive to the temperature variation. The accumulation of putrescine varied in accord with the coldness injury .The content of spermine increased greatly in January and it seemed much higher in weaker cold-resistance tree species.6) The change of lethal temperature 50(LT50) showed in a U-shaped curve and the process of low temperature adaptability could be divided into 4 stages. Cinnamomum chkiangense and Parakmeria lotungensis had a greater tolerance to low temperature and their LT50 was approximately -13℃~-19℃. But that of Manglietia insignis,Michelia chepensis Dandy and Elaeocarpus glabripetalus Merr was about -5℃~-10℃. This result was nearly the same as the analysis on morphological characters observed in the open field.7) There existed great differences of levels of coldness injury, the immerging time of symptoms and the morphological characteristics among five tree species. The leaves of Manglietia insignis showed dark boiled-like blots while the leaves of Elaeocarpus glabripetalus Merr had rusted spots under low air temperature. Leaves and tender top shoots of Parakmeria lotungensis withered. Michelia chepensis Dandy,Cinnamomum chkiangense had the similar symptoms such that leaves turned yellow ,rolled up and fell finally. According to the levels of injury symptoms immerging under the low temperature stress, the cold-resistance of 5 tree species could be ordered as : Cinnamomum chkiangense> Parakmeria lotungensis> Elaeocarpus glabripetalus Merr> Michelia chepensis Dandy> Manglietia insignis.8) According to the integrated evaluation by means of subordinate function method, the cold-resistance abilities of five tree species could be ranged as: Cinnamomum chkiangense> Parakmeria lotungensis> Elaeocarpus glabripetalus Merr> Michelia chepensis Dandy> Manglietia insignis. There was nearly no difference from the analysis result by morphological characteristics of coldness injury. |
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