扁担木叶片和次生木质部解剖和水分生理特征的可塑性

基于叶片和次生木质部解剖特征及水分生理指标观测，研究了淮北相山不同群落中扁担木的表型可塑性.结果表明，扁担木叶片结构表现出中生特点：叶为异面叶，较薄，角质层不甚发达，气孔密度较小.次生木质部表现出旱生特点：导管频率和复孔率较高，导管分子短而窄，纤维很短，射线很低.扁担木叶片、次生木质部的解剖和水分生理特征均表现出一定的可塑性，其可塑性指数高低顺序为次生木质部解剖特征（0.24）＞水分生理特征（0.19）＞叶片解剖特征（0.18）.与侧柏林和混交林相比，灌丛中扁担木个体对干旱生境有一定的适应能力，表现在次生木质部导管分子短，导管频率高，单孔率低，木纤维短，射线矮小，具有较大的相对输导率和较小的脆性指数；叶片水势、组织含水量、自由水含量较低，叶面积、比叶面积较小，而束缚水含量、束缚水自由水比值较高.扁担木的解剖和生理可塑性，使之能忍受群落演替早期的干旱生境，更好地适应演替后期的中生环境，从而成为广布种和混交林中的优势种.

Anatomical and water physiological plasticity of Grewia biloba var. parviflora leaf and secondary xylem

Based on the anatomical observations of leaf and secondary xylem as well as the measurements of leaf water physiological parameters, this paper studied the anatomical and water physiological plasticity of Grewia biloba var. parviflora growing in different succession stage communities. The results showed that G. biloba var. parviflora leaf was characterized by thin bifacial with thin cuticle and few stoma, indicating that it was mesophyte anatomically, while the secondary xylem had typical xeromorphic traits, such as short and thin vessel, high vessel frequency, low percentage single pores, and short fibers and rays. G. biloba var. parviflora had high plasticity in the anatomical structure and water physiological features of leaf and secondary xylem, and the plasticity index was in the order of secondary xylem anatomical structure (0. 24) > water physiological traits (0. 19) > leaf anatomical structure (0. 18). Compared with those growing in mixed forest and Platycladus orientalis forest, the individuals of G. biloba var. parviflora in shrub communities had the xeromorphic traits in the aspects of (1) their secondary xylem had shorter vessel elements, higher vessel frequency, less single porous percentage, lower rays, higher relative conductivity and lower vulnerability index, and (2) their leaf had lower water potential, lower water content and free water content, higher bound water content, high ratio of bound to free water content, and less specific leaf area. The phenotypic plasticity, both anatomical and physiological, made G. biloba var. parviflora tolerate to the drought at earlier succession stages and better adapt to the mesophytic condition at later stages, and consequently, become a widely distributed and dominant species in mixed forests.