Two-year-old seedlings of Michelia maudiae Dunn were grown under optimum light and water conditions for plant stability and then treated by three drop range (12, 16, and 20°C) with 12, 24, and 48 h conditions to understand the effect of short-term temperature drop (different temperature drop range and duration) on the cold resistance of plants. The overall average temperature for all treatments was 20°C. Superoxide dismutase (SOD) activities, relative electrical conductivity, soluble sugar, proline, and malondialdehyde (MDA) contents of leaves were measured, and different treatments were compared with each other. In different time conditions, the MDA content and the relative electrical conductivity were enhanced with the increased drop range and the greatest changes in the 12 h treatment; SOD activities decreased but were higher than current levels before the cooling; and soluble sugar and proline contents significantly increased in the 48 h treatment but were nonsignificant in other treatments.In different temperature drop range treatments, SOD activities and relative electrical conductivity significantly weakened with the extension of time and the greatest decrease was in the 12 h treatment. Soluble sugar and proline contents continued to increase with the greatest changes in the 48 h treatment while MDA content increased and then decreased in the 12°C drop range but increased in the 16 and 20°C drop range treatments.Finally, using the Fuzzy mathematics method, the cold resistance of M. maudiae Dunn in different temperature drop was evaluated as 12°C temperature reduction > 16°C temperature reduction >20 °C temperature reduction. This result indicates that M. maudiae Dunn has a relatively high adaptivity to the 12°C (20 to 8°C) drop rangestress.
Key words: Temperature drop range, fuzzy synthetic evaluation, cold resistance, Michelia mauldiae Dunn.
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