109 resultados para B ... n C ... f.
Resumo:
The combined occurrence of both herkogamy and dichogamy in a hermaphrodite species has been considered to strongly favour outcrossing. In this study, we investigated in detail the reproductive ecology of Gentiana straminea Maxim. (Gentianaceae), a hermaphrodite perennial endemic to the Qinghai-Tibet Plateau. In a series of observations and experiments over four consecutive years, we examined whether the combination of dichogamy and herkogamy in individual flowers completely prevents geitonogamous pollen transfer in this species. The mode of floral development clearly indicates that autonomous self-pollination is completely avoided through herkogamy and dichogamy in individual flowers. This implication was confirmed by the breeding experiments, since no seed was produced when flowers were isolated. However, this gentian proved to be highly self-compatible when geitonogamous selfing was artificially induced. Many flowers opened simultaneously on individual plants, the ratio of male to female phase flowers was close to 2:1 in each inflorescence, at the full anthesis phase, and they were randomly distributed amongst the upper, middle and lower parts of each stem's inflorescence. On average, Bombus sushikini Skorikov, the most frequent visitor and only legitimate pollinator of G. straminea, visited nearly two flowers per inflorescence, and four flowers per plant. Among the pollinators' foraging bouts, the proportions of geitonogamous visits to inflorescences or flowers within an individual plant were 29% and 37%, respectively. Therefore, despite the strict dichogamous and herkogamous characteristics of the individual flowers, geitonogamous selfing might still prevail in G. straininea because of the size of its floral displays and the continuous visiting behavior of B. sushkini. (C) 2005 Elsevier SAS. All rights reserved.
Resumo:
In the alpine region of the Tibetan Plateau, five perennial grass cultivars, Bromus inermis (B), Elymus nutans (E), Clinelymus nutans (C), Agropyron cristatum (A), and Poa crymophila (P) were combined into nine communities with different compositions and ratios, B+C, E+A, B+E+A, E+B+C,C+E+A,B+E+C+A,B+C+A+P,B+E+A+P and E+C+A+P. Each combination was sown in six 10 X 10 m plots with three hand-weeded plots and three natural-growing plots in a completely randomised design in 1998. A field experiment studied the performance of these perennial grass combinations under the competitive interference of annual weeds in 3 consecutive years from 1998 to 2000. The results showed that annual weeds occupied more space and suppressed the growth of the grasses due to earlier germination and quicker growth in the establishment year, but this pattern changed in the second and third years. Leaf area indexes (LAIs) of grasses were greatly decreased by the competitive interference of weeds, and the negative effect of weeds on LAIs of grasses declined and stabilised in the second and third years. E+B+C, B+E+C+A, and B+E+A+P possessed relatively higher LAIs (P < 0.05) among all grass combinations and their LAIs were close to five when the competitive interference of weeds was removed. Grasses were competitively inferior to weeds in the establishment year, although their competitive ability (aggressivities) increased throughout the growing season. In the second and third years, grasses were competitively superior to weeds, and their competitive ability decreased from May until August and increased in September. Dry matter (DM) yields of grasses were reduced by 29.8-74.1% in the establishment year, 11.0-64.9% in the second year, and 16.0-55.8% in the third year by the competitive interference of weeds. B+E+C+A and B+E+A+P can produce around 14 t/ha of DM yields, significantly higher (P < 0.05) than the production of the other grass combinations in the second and third years after the competitive interference of weeds was removed. It was preliminarily concluded that removal of competitive interference of weeds increased the LAIs of all grass swards and improved the light interception of grasses, thus promoting the production of perennial grass pastures. The germination stage of the grasses in the establishment year was the critical period for weeding and suppression of weeds should occur at an early stage of plant growth. The grass combinations of B+E+C+A and B+E+A+P were productive and can be extensively established in the alpine regions of the Tibetan Plateau. Two or three growing seasons will be needed before determining success of establishment of grass mixtures under the alpine conditions of the Tibetan Plateau.
Resumo:
Pollen morphology of 40 species of Rheum, belonging to eight sections, was investigated under LM and SEM. Four new exine patterns were found in the species: a) microcchinate-foveolate, b) rugulate, c) verrucate-perforate, and d) verrucaterugulate ornamentation. In addition, two patterns, the Rheum-type pollens with microechinate-perforate and fine-reticulate, as previously described, were also confirmed in the present study. Based on above study the evolution trends of pollen morphology in the taxa involved were discussed phylogenetically as below. As microechinate-perforate exine pattern existed commonly, the pattern is, therefore, regarded as the most primitive among all the six types. The fine-reticulate type was thought as a derivative type, deriving from the basic micro echinate-foveolate-perforate pattern, and followed by the rugulate and verrucate-perforate ornamentation. The verrucate-rugulate ornamentation should be the most advanced. More than one pollen type often exist in most of the sections in Rheum. The pollen morphology of Rheum was strongly correlated with its geographical and ecological distribution. Three medicinally important species R. officinale, R. palmation and R. tanguticum can be palynologically distinguished by their ornamentations.
Resumo:
本文以岩溶山区贵阳市为研究对象，利用多时相TM1）遥感图象予处理（23a）在岩溶山区城市能利用TMb）探索了一个适合于岩溶山区城市TMc）通过对TMd）制作了试验区一系列不同时相的遥感专题数据图件。通过这些专题图件可以得到试验区的资源环境现状及其变化趋势。e
