黄帚橐吾花序结构的资源配置与环境的关系

RELATIONSHIP BETWEEN HABITATS AND RESOURCE ALLOCATION OF INFLORESCENCE STRUCTURE IN LIGULARIA VIRGAUREA

为了系统地了解黄帚橐吾 (Ligulariavirgaurea)自然种群的繁殖对策 ,在其繁殖分配研究的基础上 ,通过统计不同部位头状花序的生物量投入 ,进一步分析了存在于总状花序内资源分配上的结构效应及其对不同生境条件的反应。结果表明 :1 )总状花序、不同部位头状花序在资源投入上受其栖息生境各种生态因子的影响而在不同生境和平均种群密度间存在着差异 ,并表现出一定的趋势 ;2 )可代表个体水平的总状花序大小、头状花序大小、头状花序数量和头状花序平均重量等特征 ,都与种群密度呈现出程度不同的负相关关系 ,而总状花序内不同部位的头状花序大小则与种群密度变化无关 ;3)总状花序内的资源分配存在着位置依赖性 ,这种显著差异表现为顶部头状花序比基部和中部头状花序有较大的资源分配 ;4)总状花序顶部。

In this study, we investigated resources allocation in intra_inflorescence of Ligularia virgaurea in different habitats and population densities based on the characters of reproductive allocation that have been studied. The material we studied was collected from Nima (101°53′ E, 35°58′ N, altitude 3 500 m) in Maqu county, Gansu province, in the first turn of Yellow River, North_East region of Tibetan Plateau. This region belongs to the alpine meadow rangeland type. The plot contained habitats of different degrees of degradation. L. virgaurea is a perennial herb of Compositae. The flowering phase lasts from July to August, with blooming starting at the top of the raceme. The frutescence is in September, about 10 days. It is the dominant weed in alpine meadow now because of the toxic milky material, selective predation and over_grazing by livestock. The aim of our research is to reveal the reproductive strategies of L. virgaurea at the level of the inflorescence. During the latter period of seed maturation of L. virgaurea in September 2000, we sampled randomly from three habitats, floodland, hillside and lowland, and two populations of different density in each habitat. There were 10_16 quadrates per plot, 1_3 seed producing ramets per quadrate were sampled, and brought to the laboratory. The vegetative and reproductive structures were separated, heated 24 hours in 75 ℃ drying oven, and weighed using an electronic balance (g/10 000). The ramet, raceme, capitula of different positions on the raceme, and the number of capitula per raceme were measured. The data were analyzed by ANOVA and linear regression. The measures are: the size of ramet and raceme represented by their biomass; mean weights of capitula (the ratio of biomass and numbers of capitula per raceme); the available capitula of top, middle and bottom represents separately the top, the position of 1/2 RI and the bottom; the resource allocation of capitula at different position means the biomass percent of capitula /raceme; available capitulum means it could produce seeds, unavailable capitulum means it did not. The results show: 1) different habitats or population densities differ in resource investment of raceme and capitula of different positions within raceme, and it exhibits some trends as follows: floodland > hillside > lowland, uncovered land > covered land, and low population density > high population density; 2) although most of the correlation coefficients are small, there are negative correlations between the characteristics of racemes (such as the size of raceme and capitula, the number and mean weight of capitulum) and population densities, and no correlations between the size of capitula of different positions within the raceme and population densities; 3) there is a position_based effect within inflorescences, such as the significant decrease in the resource investment between the early_formed or top capitulum of the raceme and later_formed bottom or middle capitula of the raceme; 4) there are significant negative correlations between the size of the raceme and the allocation of capitula at different positions of the raceme.