| Acacia crassicarpa is a species of multipurpose tree, which has excellent characteristics, such as fast growing and high yield, strong adaptability and drought tolerance; it also has important ecological benefit in improving soil structure and keeping fertility because of nitrogen fixation. Acacia crassicarpa originated in wet-hot climate, cold injury has become one of the principal limitations in species distribution. In this paper, two different tipes of families were determined through investigation of chilling injury, one kind was strongly cold-resistance, and the other kind was weak cold-resistance. And then,12families of Acacia crassicarpa were used as material to discuss the dynamic changes of physiological and biochemical properties, and also the tissue anatomical structure; then analyzed the differences of tested parameters from different families; and further researched the mechanisms of cold-resistance of Acacia crassicarpa; so it would establish a suitable integrated assessment system on cold-resistance of Acacia crassicarpa. Finally, this study evaluated the cold-resistance of12participating families with comprehensive indicators, in order to provide a scientific theoretical reference of early evaluation of hardness among Acacia crassicarpa families. The main results were as follows:1. The progeny forests of Acacia crassicarpa were suffered from chilling injury, there were differences in cold resistance performance and two pilots. The cold injured degree in site Datang was more serious than that in site Qinzhou. The chilling injury index of families in two pilots were integrated,10#,11#,26#,35#,41#,43#showed strongly cold resistance, while25#,33#,37#,39#,40#showed high sensitivity to chilling injury.2. Plasma membrane permeability of leaves increased during the gradient cooling process. The relative conductivity gradually increased,0℃treatment led to a substantial rise, there were significant differences among families, and the range was between58.29percent to86.50percent. The relative electrical conductivities of35#and37#family were the lowest, on the contrary, the relative conductities of25#,26#and41#were all above80percent. The semi-lethal temperature (LT50) of12families was in the range of0.49℃to5.18℃,37#was the lowest while25#and41#were the highest.3. Aactivities of protected enzymes have strengthened after low temperature treatment, increased first then decreased, the peak values of enzymes among12families were at6℃or3℃. The responses of enzyme activities to low temperature among families were different. The CAT activities of12families were obvious higher than CK, in the range of9.943u·g-1·min-1to34.182u·g-1·min-1. CAT activities of25#,26#,34#and41#were higher up to30u·g-1·min-1, while10#,33#,39#and40#were less than20u·g-1·min-1. Activities of SOD were between194.482u·g-1to389.489u·g-1,26#,33#,39#and40#decreased in contrast with CK, while other families’ SOD activities were higher than CK,34#was the highest and40#was the lowest.4. The contents of three osmotic adjustment substances were increased, displayed a dynamic change of increasing at first and then decreasing, the peak values of families were at6℃or3℃. The change extent was different among families in gradient cooling process. The soluble sugar content of families was in the range of6.904mg·g-1to15.629mg·g-1,11#,39#and40#were less while other families were higher than CK. The soluble content of25#was the highest while39#was the lowest. The soluble protein content was in the range of0.639mg·g-1to1.024mg·g-1, most of families’ were higher than CK, and35#was the highest while33#was the lowest. The content of free proline was in the range of21.405μg·g-1to52.278μg·g-1,35#was the highest while40#was the lowest.5. The MDA content increased significantly after low temperature stress, with a fluctuation change of increasing first then decreasing and increasing last. The content was in the range of7.222μmol·g-1to13.672μmol·g-1after0℃treatment. MDA content of10#and34#were significantly lower than other families, while40#and41#were the highest.6. The tissue anatomical structure of leaves changed in the gradient cooling process. The thickness of leaves, epidermis cells, palisade tissue and spongy tissue decreased, and palisade tissue and spongy tissue had obvious changes. After0℃treatment, most families kept complete structure, and the intercellular space in leaves of11#,33#,39#and40#were larger than CK, and their spongy tissue cell displayed frozen stains. The ratio of cell tense and spongy appeared relatively stable, CTR value decreased while the SR value increased as temperature dropped. The CTR value was in the range of0.38to0.45among families,43#was the biggest while11#,39#and40#were the smallest. The SR value was in the range of0.47to0.52,26#was the biggest while37#was the smallest.7.10indicators were screened which can be used to measure the cold-resistance of Acacia crassicarpa through correlation analysis. By principal component analysis, three main compositions were determined that can influent cold-resistance of Acacia crassicarpa.12families were classified into four categories base on comprehensive evaluation, with principal component synthesis model, average subjection function method and cluster analysis:34#,35#,37#and43#were strongly cold-resistance superior families; the cold-resistance abilities of25#,26#and41#were weaker than the first category; and10#,11#,33#and39#were middle cold-resistance families; while40#was the worst cold resistance family. |
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