摘要：
根系导管是植物吸收和输送水分的主要通道,导管的结构将最终决定其导水功能和效率,研究导管结构的可塑性是理解植物对干旱梯度适应机制的关键.以采自烟台-石家庄-银川-吐鲁番形成的自然梯度干旱生境中生长的酸枣植株为试验材料,采用离析法和植物显微技术,探究酸枣根次生木质部导管对梯度干旱生境适应的结构特征和机制.结果表明:酸枣根系次生木质部导管有6种类型,不同生境中同种导管的数量和形态差异较大.根据管尾情况可将导管分为三类:无尾型、一端有尾型和两端有尾型导管, 且在结构上表现出特定的适应特征及规律.从烟台至吐鲁番随干旱加剧,根系中网纹导管管壁加厚,管尾变短;孔纹导管长度、宽度、直径减小,壁厚增加,管尾变长;螺纹导管长度变小,管壁变薄,管尾变短;梯纹导管长度、宽度和直径均降低,从无尾型向有尾型转变;木纤维长度、宽度变小,管壁变薄,管尾加长.与烟台样地的导管相比,石家庄、银川和吐鲁番样地的孔纹导管长度分别减小了17.63%、11.23% 和7.67%;螺纹导管的管壁分别减小了20.2%、11.4%和14.6%;梯纹导管的长度和宽度分别减小了29.1%、37.6%、31.4%和20.7%、48.5%、28.6%;木纤维的长度分别减小了0.7%、1.5%和2.6%,宽度减小了2.2%、4.7%和5.4%,管壁厚度减小了33.2%、29.3%和22.1%.说明酸枣植株根系导管的可塑性较大,导管形态和结构的变化利于水分和养分的高效吸收和转运.导管长度、管壁和管尾的变化增强了根系的韧性和伸展能力,利于根系深扎、吸收深层土壤中的水分并快速补充植株在干旱环境中的蒸腾散失,从而适应干旱生境,保证植株的正常生长和代谢.%[Objective]Root system of a plant plays a vital role in drought tolerance. Water and nutrients are absorbed by roots, which have to adapt themselves in structure and function to adverse environments for survival, and the structure determines their function and efficiency of waterutrient translocation. However, little information is available about plasticity of the vessel in structure in the root system of the plant growing in different ecotopes. So, study on plasticity of the vessel is the key to understanding plant adaption to ecotopes along a gradient of drought.[Method]Therefore, this study was done to explore plasticity of rootvessels in structure of Ziziphus jujuba var. spinosa growing in different ecotopes, such as Yantai, Shijiazhuang, Yinchuan and Turpan along a natural drought gradient. Roots were sampled from the four ecotopes for analysis of characteristics of the vessels in the secondary xylem of the roots using segregation process and microscopy.[Result]The root vessels could be classified into six types and varied sharply in number and structure with the ecotope. The vessels could be sorted into three types according to their tail structure: no tail, tail on one end and tails on both ends, which demonstrate specific adaptive properties and regularity. From Yantai to Turpan with the drought aggravating, the reticulate vessel increased in thickness of the wall, but decreased in length of tails; the pitted vessel decreased in length, width and diameter, but did reversely in thickness of the wall and length of the tails; the spiral vessel decreased in length, thickness of the wall and length of the tails; the scalariform vessel decreased in length, width and diameter and evolved from tailless to multi-tailed; and the xylon declined gradually in length, width and thickness of the wall, but did reversely in length of the tails. In addition, compared with the tree in Yantai, the trees in Shijiazhuang, Yinchuan and Turpan had the pitted vessel decreased by 17.63%, 11.23% and 7.67% in length, the spiral vessel decreased by 20.2%, 11.4% and14.6% in thickness of the wall, the scalariform vessel decreased by 29.1%, 37.6%, 31.4% and 20.7%, 48.5%, 28.6% in length and width, and the xylon decreased by 0.7%, 1.5% and 2.6% in length, by 2.2%, 4.7% and 5.4% in width and by 33.2%, 29.3% and 22.1% in thickness of the wall, respectively. [Conclusion]All the findings indicate that the root vessels of Ziziphus jujuba var. spinosa are high in plasticity and vary in structure with the ecotope to adapt to local conditions for better adsorption and transport of water nutrients. All the changes in vessel structure improve tenacity and extendability of the roots, enabling the root to go deeper into the soil to adsorb more water from deep soil layers to make up the loss through transpiration in dry environments, thus improving the plants’resistance to drought and adaption to harsh environments to ensure normal growth.
