冬季高温对白三叶越冬和适应春季"倒春寒"的影响

暖冬和春季"倒春寒"已严重影响着多年生植物生长发育。选择建植3a的白三叶(Trifolium repens Linn)为试验材料,在入冬采用搭建塑料大棚模拟暖冬方法,通过在建棚前、建棚后、冬季融冻胁迫、春季揭棚后和"倒春寒"过程中测定棚外和棚内白三叶植株高度和叶片抗逆生理指标的变化以揭示未来暖冬对白三叶生存和生态园林持续发展的影响。结果表明,冬季棚外气温均温低于0℃,白三叶叶片经历了冻融胁迫,棚内温度高于0℃,叶片始终未结冻。搭棚前,棚内外试验地白三叶生长势无差异。搭棚后100d棚内白三叶株高是棚外的3倍,但揭棚后3个月棚内外白三叶株高一致。另外,冬季虽然棚内外白三叶叶片细胞膜透性、丙二醛(MDA)、脯氨酸、可溶性糖含量和抗氧化酶活力(SOD、CAT、POD)均随气温下降而增高与气温变化呈负相关,但棚外白三叶叶片上述生理指标均高于棚内。在春季揭棚后2d,冬季棚内生长的白三叶不仅叶片细胞膜透性和MDA含量急剧增加并高于揭棚前和棚外白三叶,而且叶片SOD和CAT活性和可溶性糖和脯氨酸含量急剧增加也明显高于棚外白三叶。在春季"倒春寒"时,冬季棚内外不同温度下生长的白三叶叶片细胞膜透性快速升高、脯氨酸和可溶性糖含量、POD和SOD活性均上升,两处理间无显著差异。研究表明,冬季零度以上低温可延缓冬季白三叶绿叶期和单个叶片的寿命,可使白三叶安全渡过春季"倒春寒",未来暖冬不会降低白三叶抗融冻能力和其返青生长势。而这与白三叶能快速应对环境温度变化,通过调整生理代谢使叶片中快速积累渗透调节物和激活抗氧化酶防止氧自由基积累抑制膜脂过氧化,保护细胞膜的完整性有直接关系。

The effect of artificial warming during winter on white clover (Trifolium repens Linn): overwintering and adaptation to coldness in late spring

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.