冬季高温对白三叶越冬和适应春季"倒春寒"的影响

Abstract

Perennial plants that normally experience dormancy during winter may be subjected to more cycles of freeze-thaw caused by warming winter.We explored the physiological mechanisms of adaptation of white clover,Trifolium repens Linn,to freeze-thaw stress.In late fall of 2009,uniform plots of white clover grown in a natural environment(NE) were covered with a plastic house(pH) to simulate the effect of a warmer winter or left uncovered(control).During the winter and following spring,growth capacity and physiological indices related to resistance to adverse environment were measured in leaves of white clover grown in both conditions.In the winter of 2009,the average temperature ranged from below zero(-10℃) to 7℃ in the NE during which leaves experienced thawing-freezing-thawing-freezing,and above zero(from 1 ℃ to 7 ℃) in the pH where leaves were never frozen.In late fall of 2009,all white clover was of uniform height.But in spring 2010,plants grown in the PH(26 cm) were 3 times taller than those in the NE(8 cm).This difference in height disappeared by June 2010.In winter,the relative membrane permeability,MDA(malondialdehyde),proline,and soluble sugar contents,and the activities of catalase(CAT) and superoxide dismutase(SOD) and peroxidase(POD) increased with decreasing temperature in leaves of white clover grown in both NE and PH.The physiological index values in the white clover grown in the NE experiencing freezing-thaw stress was greater than those in leaves grown in PH(no freezing).In spring,two days after removing the plastic housing,the relative membrane permeability and content of MDA in the leaves of white clover rose quickly to 127% of values before removing the PH,and even higher than that in the leaves of white clover grown in the NE.Activities of SOD and CAT in white clover after removing the PH also increased quickly to 33% and 84.6% higher than in white clover grown in NE.In addition,during late spring coldness,plants in both treatments showed the same trend of increasing proline and soluble sugar content and activities of POD and SOD in response to lower temperature.Our results suggest that Trifolium repens has a high capacity to activate antioxidant enzyme activity to control lipid peroxidation and increase osmolytes in response to freezing temperature and that these mechanisms play a key role in surviving warm winter.While a warming winter delays the greening period,it does not retard white clover growth in spring,making white clover an excellent plant to withstand climate changes that include warmer winters.