内蒙古高原锦鸡儿属植物的形态和生理生态适应性

比较研究内蒙古高原锦鸡儿属(Caragana)中生种,旱生种和强旱生种的叶片形态结构、渗透调节、气孔调节和保护酶,目的是揭示锦鸡儿属不同类型植物的生态适应策略。中生种叶片平展,被稀疏绿色短柔毛;旱生种叶片平展或呈瓦状,被灰色柔毛;强旱生种叶片呈瓦状或卷成筒状,被直立或伏帖绢毛。叶片厚度强旱生种>旱生种>中生种,叶片面积、生物量和比叶面积(SLA)强旱生种<旱生种<中生种。叶片长宽比,强旱生种和旱生种大于中生种。这些形态结构导致保水能力强旱生种>旱生种>中生种,光能利用能力中生种>旱生种>强旱生种。渗透调节物质含量、细胞质离子浓度和细胞渗透势强旱生种>旱生种>中生种。渗透调节物质含量的差异主要表现在强旱生种可溶性糖和无机离子含量远高于旱生种,后者又远高于中生种。叶含水量、自由水含量、叶水势和气孔导度中生种>旱生种>强旱生种,束缚水含量、束缚水/自由水比值、POD和SOD活性正好相反,CAT活性旱生种>中生种>强旱生种。这些生理特性导致抗旱能力强旱生种>旱生种>中生种,但代谢速率正好相反。旱生种和中生种表现出较少的日水分亏缺,强旱生种水分亏缺从清晨到傍晚持续大幅增加。细胞膜相对透性和MDA含量强旱生种>旱生种>中生种。自由基含量表现为旱生种>中生种>强旱生种。这些数据说明虽然旱生种和强旱生种形成了多种特点来适应干旱环境,但仍然是不充分的。结论:(1)分布于半湿润至半干旱区的锦鸡儿属中生种依靠活跃的代谢、大量的水分消耗和快速生长使其在生物环境中取得竞争优势;生活在干旱地区和强干旱地区的旱生种和强旱生种依靠低代谢、节水和高抗旱性来抵抗苛刻的非生物环境。(2) 旱生种和强旱生种主要通过可溶性糖和无机离子的积累,调节细胞质渗透势,保持水分平衡,这是一种相对节省能量的适应对策。

Morphological and physiological adaptation of Caragana species in the Inner Mongolia Plateau

The morphological structure, osmotic adjustment, stomatal regulation and antioxidative enzymes of mesophilous, xerophilous and super- xerophilous species of Caragana were studied, in order to understand their ecological adaptation mechanisms. The results showed that flat leaves with few green villi were common in mesophilous species, tile-shaped leaves with offwhite villi were common in xerophilous species and tile-shaped or tube-shaped leaves with densely vertical or fallen silky villi were common in super-xerophilous species. Leaf thickness was greatest in super-xerophilous species, less in xerophilous species, and least in mesophilous species. Leaf area, leaf biomass, and specific leaf area (SLA) were highest for mesophilous species, with xerophilous species having lower values, and super-xerophilous species having the lowest values. The thickness-area ratio and length-width ratio in super-xerophilous species and xerophilous species were greater than those in mesophilous species. With these morphological features, the water retention capability was highest in super-xerophilous species, and lower and lowest in xerophilous and mesophilous species, respectively; conversely, light use capability was highest in mesophilous species, followed by xerophilous and super-xerophilous species, respectively. The osmotic adjustment substances content, cytoplasmic ion concentration and osmotic potential of super- xerophilous species were the highest, with those of xerophilous species being intermediate and those of mesophilous species being the lowest. The most obvious differences in osmotic adjustment substances content were that the soluble sugar and inorganic ion contents decreased substantially from super- xerophilous to xerophilous and then to mesophilous species. The leaf total and free water content, leaf water potential, as well as stomatal conductance were highest in mesophilous species, intermediate in xerophilous species and lowest in super- xerophilous species, whereas the bound water content, ratio between bound and free water, peroxidase (POD) and superoxide dismutase (SOD) activity were in the reverse order. Catalase (CAT) activity was highest in xerophilous, intermediate in mesophilous, and lowest in super- xerophilous species. These ecophysiological characteristics resulted in different drought resistance ability and metabolism intensity among Caragana species. Super-xerophilous species had the strongest drought resistance, while xerophilous species had medium drought resistance and mesophilous species had the lowest drought resistance, whereas the metabolism intensity was the highest in mesophilous species, intermediate in xerophilous species and lowest in super-xerophilous species. The diurnal water deficit of xerophilous and mesophilous species was low, and super-xerophilous species had gradually increasing diurnal water deficit from dawn to dusk. Both permeability of plasma membrane and malondialdehyde (MDA) content were greatest in super-xerophilous species, intermediate in xerophilous species, and least in mesophilous species. Free radical content was highest in xerophilous species, with mesophilous and super-xerophilous species having intermediate and lowest values, respectively. These results indicated that although the xerophilous and super-xerophilous species had evolved many morphological and physiological characteristics to cope with the arid environment in desert, their adaptation might still be insufficient. From this study, we can draw two main conclusions: (1) The morphological and physiological characteristics of Caragana species vary in accordance with the environmental conditions of their distribution areas in the Inner Mongolia Plateau. The wide range of variation in morphological and physiological characteristics may be the biological base for the broad distribution of Caragana species in the Inner Mongolia Plateau. With an active metabolism, fast growth and high water consumption, mesophilous Caragana species have strong competitive ability. A low metabolism, economical water use strategy and strong stress tolerance, especially to drought, enables xerophilous and super-xerophilous Caragana species to thrive in harsh environmental conditions. (2) Xerophilous and super-xerophilous Caragana species adjust their cell osmotic potential mainly through accumulating soluble sugars and inorganic ions, which are probably energy-saving adaptation strategies in stressful environments with less productivity.