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Low temperature stress is one of the major environmental factors affecting the process of physiology and photosynthesis of plants,which is known to cause many physiological and biochemical changes in plant metabolism such as protein denaturation,lipid liquefaction,the increased activity of antioxidant enzymes or perturbation of membrane integrity.Also low temperature decreases capacity and efficiency of photosynthesis.Therefore,the above physiological and biochemical indexes and photosynthetic characteristics are often used as an indicator of stress injury in plants.In response to low temperature stress,plants naturally have developed diverse mechanisms which can mitigate the effect of stress and lead to the adjustment of plant tolerance.Effects of low temperature stress on physiological-biochemical indexes and photosynthetic characteristics were studied in the seedlings of Rhus chinensis,Duranta repens,Thunbergia erecta and Pueraria lobata.Results showed that(1) with increasing time of low temperature,the chlorophyll content of D.repens seedlings increased initially and then decreased,whereas that of the other three seedling types continuously decreased,and it rebounded significantly after removal of low-temperature stress for the four seedling types.The free proline content of the four seedling types gradually increased or fluctuated;the soluble protein content of P.lobata seedlings increased followed by an decrease,whereas the other three seedling types continuously increased,and that of the seedling types except for P.lobata rebounded significantly after low-temperature stress relieving;the contents of soluble sugar and MDA of the four seedling types tended to increase,their SOD activity continuously rose or rose initially and then fell,and SOD activity of the seedling types except for R.chinensis declined significantly after low-temperature stress relieving.(2) With increasing low temperature time,the net photosynthetic rate(Pn),stomatal conductance(Gs) and transpiration rate(Tr) continuously decreased for the four seedling types,and the intercellular CO2 concentration(Ci) of D.repens continuously increased,whereas that of the other seedling types decreased followed by an increase.The Pn,Gs and Tr of the four seedling types increased to some extent,whereas their Ci decreased to some extent after low-temperature stress relieving.Increase in contents of free proline,soluble protein and soluble protein and increase or stead in SOD activity for the four seedling types alleviated degree of membrane lipid peroxidation of seedling cells and protected cell membrane,which is important regulatory mechanism of seedlings to low temperature stress.(3) The physiological indexes and photosynthetic indexes of the four seedling types were evaluated using principal component analysis,indicating that their ability of low temperature resistance was P.lobata R.chinensis T.erecta D.repens.During low temperature stress and low-temperature stress relieving,osmotic substance content and SOD activity kept steady or increased in the seedlings of four plant species,and their Pn,Gs and Tr increased to some extent and Ci increased to some extent after low-temperature stress relieving,indicating that they had some ability of low temperature resistance.This result could supply scientific basis for plant selection in restoration of abandoned quarries.

Leaf traits reflect use-efficiency strategies in plants.The manner in which leaf traits change within or across species can profoundly affect plant growth,reproduction and ecosystem function.The morphological characteristics of plant leaves are greatly influenced by environmental factors associated with climate and light.Morphological plasticity plays an important role in resource acquisition of plants and variations in leaf trait is of major importance for plant adjustment to resource availability.Changes in temperature and rainfall patterns are predicted to significantly influence morphological plasticity of plant leaves.Leaf morphology of native vegetation has often been interpreted as a sensitive indicator of environmental conditions.The relationship between climate and leaf plasticity is universal and particularly important in certain ecosystems,because of their enormous size and correspondingly vast stores of carbon.Tree ecologists with an interest in leaf dynamics have typically concentrated on assessing a limited number of variables,such as leaf length and width,leaf area and leaf weight.However,assessing the leaf dynamics of forest trees is especially challenging since turnover is often high and there is abundant variation in leaf phenotypic characteristics between and within individuals,populations and species.The correlation between leaf length and leaf width and changes of leaf mass per area(LMA) were studied in seedlings of Elaeocarpus sylvestris,Mytilaria laosensis,Cinnamomum camphora,Camellia semiserata,Ormosia pinnata and Castanopsis hystrix,in order to understand change of leaf shape of the six broadleaf seedlings and climate effects on their leaf changes.The very significant correlation existed between leaf length and leaf width of the six seedlings.The month changes of correlative coefficients of most seedlings were intimate with season change.The six seedlings were divided into two types according to leaf similarity change: a),correlation change with season including E.sylvestris,C.semiserata,O.pinnata and C.hystrix;b),steady correlation including C.camphora and M.laosensis.The correlation between leaf length and leaf width changed with rainfall amount according to a linear relationship,and there was a binomial relationship between the correlation and mean temperature as well as between the correlation and illumination time.The LMA changed with seedling species and season and the change was great in the first half year and small in the second half year.The LMA of young leaf was greater than old leaf in the first half year whereas it was close to that of old leaf in the second half year.The change in LMA of old leaf for the six seedlings was small throughout whole year whereas that of young leaf in the first half year was greater than in the second half year.In the first half year the LMA of young leaf for the same seedling was greater than old leaf,whereas they were the similar to each other in the second half year.The LMA of young and old leaves of C.semiserata seedlings was significantly greater than that of other seedlings.The LMA of the six seedlings changed with rainfall amount,mean temperature and illumination time according to a binomial relationship.