基于植物分割理论的毛白杨干旱落叶研究

Leaf shedding of Populus tomentosa under drought stress based on the theory of plant segmentation hypothesis

【目的】毛白杨是我国华北和西北地区优秀的造林树种,而华北西北地区是我国干旱胁迫最严重的区域,季节性、偶发性严重干旱时有发生。毛白杨在干旱季节会出现少许落叶甚至全部落叶的情况,能有效的减少水分蒸发保存核心器官水分,复水后重新展叶度过干旱。本研究以毛白杨品种北林雄株1号、北林雄株2号为植物材料,基于植物分割学说从植物器官的水力分割和脆弱性分割的水分关系上分析干旱季节落叶的原因。【方法】对毛白杨两个品种的茎干、叶柄、叶片的水力性状、功能性状进行了比较研究。【结果】(1)两者的脆弱性曲线Ψ50值的排序为叶>茎干>叶柄,在一定程度上是符合植物分割学说,叶片比茎干更脆弱。(2)比叶质量和茎干木材密度都是碳储量指标,比叶质量和叶片寿命有关,木材密度与植物的抗空穴化和栓塞修复能力有关。和树木的一般数值比较,北林雄株1号、北林雄株2号的比叶质量较低,表明叶片寿命较短;木材密度一般,说明茎干的抗空穴化能力一般。【结论】毛白杨水力和脆弱性数据基本符合植物分割学说,说明可以在其保持茎干水分下落叶。叶片比较低的寿命和茎干较弱的抗空穴化和栓塞修复能力,也需要落叶来应对严重干旱逆境。揭示了毛白杨既能在水肥充足的条件下快速生长,又能在偶发的比较极端的干旱条件下通过落叶来保持生存的水力学原因。当然干旱落叶复生还可能涉及其体内特殊的生理生化机能,有待进一步研究。

[Objective]Populus tomentosa is an excellent afforestation species in northern and northwestern China.Seasonal and occasional severe droughts occur in this region,and it is the most severe area of drought stress in China.P.tomentosa may fall a little leaves or even all leaves in the dry season,which can effectively reduce the evaporation of water to preserve the core organs,and grow the leaves again to survive the drought after rehydration.In this study,P.‘Beilinxiongzhu 1’and P.‘Beilinxiongzhu 2’,the varieties of P.tomentosa,were used as plant materials.Based on the plant segmentation hypothesis,the causes of leaf shedding in the dry season were analyzed from the hydraulic relationship of plant organs between hydraulics segmentation and the vulnerability segmentation.[Method]The hydraulic characteristics and functional traits of stems,petioles and leaves of two varieties of P.tomentosa were compared.[Result](1)The order ofΨ50 values of the vulnerability curves of the two trees was leaf>stem>petiole,which was in consistent with the plant segmentation hypothesis to some extent,and the leaves were more vulnerable than stems.(2)Specific leaf mass and stem wood density were carbon storage indicators.The specific leaf mass was related to leaf life and the wood density was related to the ability of anti-cavitation and embolization.Compared with the general values of other trees,P.‘Beilinxiongzhu 1’and P.‘Beilinxiongzhu 2’had smaller specific leaf mass,indicating that the leaves had a shorter life and the wood density was general,indicating that the resistance of the stem to cavitation was general.[Conclusion]The data of hydraulics and vulnerability of P.tomentosa can be explained by plant segmentation hypothesis,which showed that it can defoliate under the condition of keeping water in the stem.The lower life span of leaves and the weaker resistance of stems to cavitation and embolism also need defoliation to deal with severe drought.It reveals the hydraulic reasons for the rapid growth of P.tomentosa under the condition of sufficient water and fertilizer,and the ability to survive through the defoliation under the occasional extreme drought conditions.Of course,the regrowth of leaves may also involve special physiological and biochemical functions,which needs further study.