作 者 ：任明迅, 张全国, 张大勇
期 刊 ：植物生态学报 2004年 28卷 6期 页码：753-760
Keywords:Eichhornia crassipes, Breeding system, Biological invasion, Evolution,
摘 要 ：对中国境内的凤眼蓝（Eichhornia crassipes）进行了大规模地理范围的调查，分析了24个地点40个种群的克隆繁殖与有性繁殖的相对水平、三型花柱的花型变化以及花部综合特征的变异。40个种群都以克隆繁殖为主要更新方式。其中36个种群只有三型花柱中的M花型；南宁、重庆的种群中出现了频率极低的L花型；南宁、重庆、福州和海口种群内，出现了具有促进花内自交潜能的半同长花柱花型（柱头与花药相靠拢的M花型变异体或L花型变异体）。与其它地方种群相比，西南和海南岛的种群表现出较多样化的繁育系统。M和L花型个体的结实个体率都约为4％，没有显著差异，种子产量在两花型个体之间也没有差异。由于种群内花型的残缺，作为促进花型之间异交传粉适应机制的三型花柱繁育系统已经解体，部分种群中出现了可以促进花内自交的半同长花柱变异体。克隆繁殖是凤眼蓝适应入侵生境的一种形式，花内自交是凤眼蓝繁育系统在入侵过程中可能的进化方向，这些繁育系统上的变化对该植物的入侵机制和途径产生了深远影响。
Abstract:Knowledge about the breeding systems of invasive weeds is crucial for invasion management. Eichhornia crassipes, a noxious clonal plant, has a complex breeding system that includes clonal reproduction and a special sexual reproduction mode, tristyly, and a complex mating system that consists of three floral morphs that differ in the length of styly and stamens. In this paper, we compared the breeding systems of 40 Eichhornia crassipes populations in 24 localities throughout China by investigating the relative level of sexual and clonal reproduction, number of floral morphs and the variances in floral syndrome (especially the position of sexual organs) for each population. A Mann-Whitney test was used to detect whether the variation in the position of the sexual organs were significant among each other and the typical floral morphs. The seed-set ratio of each floral morph was investigated extensively in a Chongqing population that had a high number of floral morphs. All the populations were regenerated primarily by clonal propagation as a result of vigorous clonal growth. Sexual reproduction was presumably constrained because only one or two floral morphs existed in the populations. Sexual recruitment was further restricted by lack of suitable ecological conditions for seed germination and seedling establishment. Exposure to the sunlight and water temperature above 30 ℃ is generally necessary for seed germination, a condition not met in most populations. Most of the populations surveyed were monomorphic for the M floral morph, and only the populations in Chongqing (West China on the Yangtze River) and Nanning (Southwest China near the tropical zone) contained the L morph with the M morph still predominating the populations. No significant differences in the fecundity of the M and L morphs were found and only 4% of the individuals produced seeds for these two floral morphs. The number of seeds per capsule varied greatly in both morphs, from 13 to 296 in the L morph and from 20 to 230 in the M morph, which suggested that fecundity was greatly restricted by ecological conditions, such as pollination and weather conditions, rather than developmental deficiency. The variations in the position of the sexual organs in the M floral morph were not significantly different among each other and the typical flowers. But, populations in Chongqing, Nanning, Fuzhou and Haikou were found to have modified M morphs or L morphs with anthers and stigma adjacent to each other (namely semi-homostylous flowers). Semi-homostyly is thought to be controlled by modifier genes and is selected for since it can increase fecundity through autogamy in invaded regions that have unreliable and inefficient pollinators. Based on the relative levels of sexual reproduction and number of floral morphs in a population, our results showed that the breeding systems of populations in the southwestern region and on Hainan Island were much more diverse than in other regions. The evolutionary trend of the breeding systems that occurred in some E. crassipes populations is consistent with the Baker‘s law, which states that autogamy would be favored during an invasion event. These evolutionary changes of the breeding systems also have significant effects on the invasion process of this species.