闽南花岗岩堡状峰乌冈栎种群的表型变异

Phenotypic variation of Quercus phillyreoides populations on castle peak of South Fujian, China

关键词:  陆地岛屿系统, 乌冈栎, 叶显微性状, 自然选择, 种群分化

Key words:  continental island system, Quercus phillyreoides, leaf microscopic character, natural selection, population differentiation

摘要:

堡状峰是类似城堡外貌而凸出于周围环境之上的特殊山峰,位于中国闽南乌山风景区堡状峰地貌上的乌冈栎(壳斗科)种群的表型发生了变异,其与原类型的显著不同在于叶背具宿存性黄褐色星状毛。为解释这一现象,该研究对堡状峰顶部的乌冈栎种群分布进行调查,包括其中的变异型、原始型、过渡型,以及堡状峰山脚、另一异域的典型原始型种群被研究,基于叶表皮解剖,利用方差分析统计显微性状的差异,结合生态因子,探究变异的原因及演化的可能途径。结果表明:(1)变异型在山顶西侧形成以其为优势种的常绿阔叶灌丛群落,东侧的小片灌丛以原始型为主,后者内部还有少量过渡型。(2)各种群单细胞毛状体基(STB)与复合毛状体基(CTB)在叶上表皮的密度很小甚至小于每平方毫米1个,宏观的表现为无毛。原始型、过渡型、变异型的STB密度均值在叶下表皮递增。变异型种群与原始种群相比,叶下表皮CTB或典型星状毛(Tst)的密度由每平方毫米0.481～1.122个变异至每平方毫米57.2个,宏观表现为形成密毛。气孔长宽比在原始型(1.187～1.205)至变异型(1.258)间递增。(3)方差分析结果显示,变异型叶下表皮STB与CTB密度及气孔长宽比较原始型显著增加(大)(P<0.01),但气孔密度与尺寸在种群间未表现出规律与差异性(P>0.05)。乌山堡状峰顶的土壤贫瘠、水热条件差。综合生境与统计的结果表明,变异型乌冈栎叶背毛状体及气孔长宽比的变异具抵抗干旱或极端气温的功能。由于花粉流未曾间断,因此相比于地理隔离,特殊生境促使乌冈栎发生适应性演化应是该变异产生的主要原因。该研究为亚热带特殊花岗岩地貌促进种群分化和物种形成提供了直接的证据。

Abstract:

Castle peak is a mountain that resembles the appearance of a castle and protrudes above its surroundings. The phenotypes of Quercus phillyreoides(Fagaceae)populations located on castle peak in the Wushan Scenic Spot of southern Fujian, China, are variegated. It differs significantly from the original form in the presence of persistent yellow-brown stellate hairs on the leaf abaxial surface. To explain this phenomenon, the distribution of Q. phillyreoides populations at the summit of castle peak was investigated, where variant, original, and intermediate forms, as well as typical original populations at the foot of castle peak and another allopatric area, were studied. Differences in micromorphological traits were counted using ANOVA based on leaf epidermal anatomy. Ecological factors were linked with a view to discovering the causes of variation and possible pathways of evolution. The results were as follows:(1)The variant form formed an evergreen broad-leaved scrub community with it as the dominant species on the west side of the summit, and the small patch of scrub on the east side is dominated by the original form, with a few intermediate form individuals within the latter.(2)The densities of single trichome base(STB)and compound trichome base(CTB)in the leaf adaxial epidermis of various populations was very low or even less than 1 No.·mm^-2, and the macroscopic expression was glabrous. The mean values of STB density of original, intermediate, and variant forms were increasing in the leaf abaxial epidermis. The mean density of CTB or typical stellate trichome(Tst)on the leaf abaxial epidermis varied from 0.481-1.122 No.·mm^-2 to 57.2 No.·mm^-2 in the variant form population compared with the original form populations, which macroscopically showed the formation of dense hairs. The stomatal length-width ratio increases from original form(1.187-1.205)to variant form(1.258).(3)ANOVA results showed that variant form leaf abaxial epidermal STB, CTB density and stomatal length-width ratio were significantly increased(larger)than the original form(P<0.01), but stomatal density and size did not show regularity and variability among populations(P>0.05). Poor soil, water and heat conditions at the summit of the Wushan castle peak, and combining the background with the obtained results indicate that the variation in the variant Q. phillyreoides leaf abaxial trichomes and stomatal aspect ratio were resistant to drought or temperature extremes. Since pollen flow has not been interrupted, the adaptive evolution of Q. phillyreoides due to specific habitats should be the main reason for this variation compared to geographical isolation. The microscopic traits showed no significant differences(P > 0.05)between the original form population on the top of castle peak and the rest original form populations confirms that the variation has been fixed by long-term selection and the short-term environmental influences play a limited role in shaping the variant traits. This study provides direct evidence that subtropical exceptional granitic landforms promote population differentiation and species formation.