分析干旱胁迫下胡杨(Populus euphratica Oliv.)茎木质部解剖结构与水力特性的变化对解读其抗逆性机理具有重要意义。本文采用水分控制试验, 分析胡杨幼株茎木质部解剖结构和水力特性对不同土壤干旱胁迫处理的响应。结果表明: 在解剖结构方面, 随着干旱胁迫的加剧, 胡杨茎木质部导管密度呈极显著减小(P<0.01)趋势, 而导管内径、导管壁厚度、管壁机械强度呈极显著增大(P<0.01)趋势, 穿孔直径和纹孔直径显著增大(P<0.05); 但导管分子形态却没有发生显著变化, 都具有孔纹式和螺纹式两种类型, 其中纹孔多为具缘纹孔, 呈互列式排列, 端壁穿孔为单穿孔类型, 并具有螺纹加厚现象; 在水力特性方面, 随着干旱胁迫的加剧, 胡杨茎的木质部比导率(Ks)和自然栓塞程度(PLC)呈显著增加趋势(P<0.05)。为了适应干旱的环境, 胡杨茎木质部结构和水力特性发生相应的变化, 一定程度上弥补了干旱胁迫所带来的不利影响。
Populus euphratica Oliv. is a precious woody plant in arid regions with vital ecological functions such as high tolerance to salinity/alkalinity, high drought resistance, wind-break/sand-fixation, etc. Because of human socio-economic activities and the resulting development of water resources in recent years, a large number of P. euphratica decayed. Current studies on P. euphratica have focused on changes in physiological and biochemical characteristics, changes in dominant P. euphratica community characteristics, vitro morphogenesis development and histological trend observations. However, there have been little studies on the anatomy and hydraulic characteristics of xylem stems under drought stress. Analysis of changes in the anatomy and hydraulic characteristics of P. euphratica stem xylem under drought stress was significant for interpreting its resistance mechanism. This water control experiment analyzed the response of the anatomy and hydraulic characteristics of P. euphratica stem xylem to different degrees of drought stress. Results showed that with increasing drought stress, the xylem vessel density significantly decreased (P < 0.01). Also xylem vessel diameter, wall thickness and wall mechanical strength increased significantly (P < 0.01). The large the vessels diameter, the more water transported. Also thicker and harder vessel walls ensured secure water relay. Perforation and pit diameters also significantly increased (P < 0.05) with increasing drought stress, resulting in more efficient axial and radial water relay. However, no observable changes were noted in vessel micro-morphology. There were two types of vessel ― pitted vessel and spiral vessel. Most of the pits were bordered pits with alternate arrangement. Spiral thickening was noted at end walls of vessel. All perforations were of the single type, probably due to common natural growth and long-term evolution. For hydraulic characteristics, conductivity (Ks) and native embolism level (PLC) significant increased (P < 0.05) with increasing drought stress. To effectively adapt to arid environments, it was concluded that changes in anatomy and hydraulic characteristics of P. euphratica stem xylem were active growth processes. To a certain extent, these activities compensated for the negative effects of drought stress on P. euphratica.