Xylem Anatomical Structure And Response To Environment Of Mangrove

The xylem is mainly composed of parenchyma,vessel and fiber,which are used for storage,transport and support,respectively.Because the space of xylem is limited,the space proportion of each tissue is mutually restricted.With the change of environmental conditions,the configuration of xylem tissues changes in order to adapt to the specific environmental factors.The study of xylem structure and relationship with environmental changes can reflect the ecological adaptation strategies of plants and contribute to the protection and utilization of plants.In this study,thirteen mangrove plants in four distribution points of coastal latitude gradient were selected as research materials,through the determination of xylem structure and functional traits,analysis the correlation between the xylem traits of mangrove plants and the effects of different environmental conditions on xylem traits.aimed to understanding coast intertidal zone mangrove plants habitat adaptation strategy.The results showed that:(1)In mangrove,rhizophoraceae and non-rhizophoraceae species have different adaptation strategies in water use.Rhizophoraceae rely on strong antiembolism ability trapezoidal perforation and better storage function of parenchyma to ensure the safety of water transport,while non-rhizophoraceae mainly rely on single perforation and more vessel lumen fraction to improve the efficiency of water transport.(2)In tropical,subtropical typical plants(magnolia plants),both axial parenchyma fraction and vessel to axial parenchyma connectivity promoted water transport efficiency,while mangrove showed no significant correlation between axial parenchyma fraction and hydraulic conductivity.However,the species with higher vessel to axial parenchyma connectivity had higher water transport efficiency.The axial parenchyma of mangrove with different arrangement patterns has different functions,and the circular vessel arrangement structure is beneficial to water transport.(3)Compared with the global xylem tissue fraction,mangrove have higher parenchyma fraction and lower fiber fraction,but there is no significant difference in the vessel fraction;there is a significant trade-off relationship between the parenchyma and fiber,and there is no significant correlation between the vessel fraction and parenchyma,fiber fraction.As the main structure of water transport,vessel forms a relatively stable fraction in the evolutionary process,mangrove adapt to special habitats mainly by adjusting xylem fiber and parenchyma fraction.(4)When the environment changed,the axial parenchyma fraction and vessel to axial parenchyma connectivity of mangrove changed,which were mainly decreased with the increase of mean annual temperature and salinity,and increased with the increase of mean annual precipitation.The influence of mean annual temperature and salinity is greater than that of mean annual precipitation.There were no obvious changes in the structures of vessel,fiber and ray parenchyma.(5)Studies on the plasticity of Kandelia obovata,Bruguiera gymnorrhiza and Avicennia marina of locally distributed species were conducted,the axial parenchyma fraction of K.obovata,and B.gymnorrhiza showed strong plasticity.Although the axial parenchyma cell plasticity of A.marina was lower than that of K.obovata,and B.gymnorrhiza,the special structure of secondary phloem and continuous cambium in the xylem made A.marina better adapted to each niche.In conclusion,mangrove have stable vessel fraction,low fiber fraction,high parenchyma fraction and axial parenchyma greater plasticity.Environmental conditions ultimately determine the fraction and spatial distribution of axial parenchyma,which reflects the adaptation mechanism of mangrove in special habitats.