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971.
Summary
Fragaria chiloensis is a stoloniferous perennial herb that grows on coastal sand dunes where scattered shrubs create small patches of lower photon flux density (PFD) but higher soil nitrogen availability. The potential effects of resource transport between ramets when PFD and soil nitrogen are negatively associated in space were tested by comparing the growth of pairs of ramets in which the vascular connection between ramets was either severed or left intact. One ramet in each pair was given high PFD but a low level of soil nitrogen and the other ramet was given low PFD but high N. The analogous effects of resource transport likely to be realized in nature were tested by substituting a more realistic medium soil nitrogen level in place of the high level. Results suggested that connected ramets exchanged carbon and nitrogen under both regimes of soil nitrogen heterogeneity. In the low versus high nitrogen regime, connected ramets had higher combined dry biomass and different patterns of dry mass partitioning from those of severed ramets; effect of connection was greater on ramets given low PFD and high N and on younger ramets. In the low versus medium nitrogen regime, connected ramets had different patterns of partitioning only. Apparent reciprocal resource transport between ramets can enhance the growth of ramets with complementary resource deficiencies, but may affect growth in dry mass only when maximum resource levels are high. 相似文献
972.
Summary The photosynthetic pathways of 42 species of the genusEuphorbia growing wild, naturalized or cultivated in Egypt were investigated. The criteria used included the δ13C- and δD-values and Kranz anatomy of the leaves. There is a relationship between the photosynthetic pathway and the ecological
conditions in the habitat of a particular species. All 4 CAM species are succulent shrubs, wild or cultivated. The 11 species
with C4 pathways are mainly summer annuals of tropical origin and flourish under the hot summer conditions. The 27 C3 species are either winter annuals, perennials, perennials flourishing in winter or shrubs; the majority are Mediterranean,
European or Saharo-Arabian. Summer annuals with C3 pathways grow under the shade of the summer crops. Generally, C3 plants grow under conditions of relatively better water resources and lower temperature than the C4 plants. The majority of the CAM and C4 species occur in the southern part of the country, where high temperature is a common feature of the climate. 相似文献
973.
About 20 different carotenoids were found in a strictly aerobic photosynthetic bacterium, Erythrobacter longus. All the carotenoids except the highly polar ones were identified as C40-skeletal carotenoids, which could be devided into three groups: (1) bicyclic carotenoids: -carotene and its hydroxyl derivatives; -cryptoxanthin, zeaxanthin, caloxanthin and nostoxanthin, (2) monocyclic carotenoids: rubixanthin, bacteriorubixanthin and bacteriorubixanthinal, which was a unique cross-conjugated carotenal, and (3) acyclic carotenoids: anhydrorhodovibrin and spirilloxanthin. Bacteriorubixanthinal and zeaxanthin were the major components. (3R)-3-Hydroxy--ionone has rarely been found in carotenoids of purple photosynthetic bacteria, while the acyclic carotenoids have been found exclusively in photosynthetic bacteria. Thus, this bacterium is interesting in its composition of carotenoids.Abbreviations DPA
diphenylamine
- HPLC
high-performance liquid chromatography
- HP-TLC
high-performance thin layer chromatography
- FD-MS
field desorption mass spectrometry
-
1HNMR
proton nuclear magnetic resonance
- CD
circular dichroism 相似文献
974.
C_4.植物鼠尾粟(Sporobolus indicus),金色狗尾草(Setaria glauca)、细叶结缕草(zoysia tenuifolia)、千金子(Leptochloa chinensis)和 CAM 植物芦荟(Aloe vera)属PEP 羧激酶亚型。C_4双子叶植物飞扬草(Euphorbia hirta)则为 NAD 苹果酸亚型。前面4种 PEP 羧激酶型的 C_4草本植物的维管束鞘细胞叶绿体呈均匀分布,与已知的该型的离心排列不同。认为这可为 C_4植物三种光合亚型的演化关系提供新的证据。 相似文献
975.
On nonparametric kernel density estimates 总被引:1,自引:0,他引:1
976.
Microsite variation in light availability and seedling growth ofQuercus serrata in a temperate pine forest 总被引:1,自引:0,他引:1
Spatial heterogeneity in light availability for tree seedlings under the canopy of a temperate pine forest was studied. Six-day
measurements at 10-s intervals revealed a great variety in the temporal patterns of photosynthetic photon flux density (PPFD)
and histograms among observation days and microsites; mean daily total PPFD relative to full sun varied from 1.5% to 10.4%
depending on the microsites. The occurrence and duration of PPFD above 80 μmol m−2 s−1, which might reflect sunfleck activity, varied greatly among the microsites. However, several simple empirical relationships
were found between some parameters characterizing microsite light availability and sunfleck activity; the diffuse site factor
was correlated well with other parameters, including daily total PPFD, daily totals and daily summed durations of high PPFD
above any examined threshold level, and its contribution to daily total PPFD. Diffuse site factors which were obtained for
700 microsites within an area of 28 m2 on three different occasions during the growing season showed high correlations within the microsite. Based on the regressed
relationship between the relative growth rate of current-year seedlings ofQuercus serrata and the microsite diffuse site factor and the results of area-survey measurement of the diffuse site factor, an estimation
was made of the abundance of potential ‘safe-sites’ for seedling growth of the species; the ‘safe sites’ were estimated to
cover 40% and 0% of the total area of the sunny and shady sites of the forest, respectively. 相似文献
977.
Pulsed field gel electrophoresis of representatives of Mycobacterium tuberculosis and Mycobacterium bovis BCG strains 总被引:1,自引:0,他引:1
Anne Varnerot Françoise Clément Marina Gheorghiu Véronique Vincent-Lévy-Frébault 《FEMS microbiology letters》1992,98(1-3):155-160
Abstract Using field inversion gel electrophoresis (FIGE), different Mycobacterium tuberculosis strains, such as phage prototypes, exhibit different DNA restriction patterns which are easy to compare. Virulent and avirulent variants of M. tuberculosis H37, as well as daughter strains of M. bovis BCG, display characteristic DNA profiles. BCG strains isolated from suppurative adenitis following vaccination of French patients showed patterns identical to the BCG Pasteur strain used for vaccination. These results demonstrate that FIGE of DNA restriction fragments generated by Dra I represents a suitable technique for the analysis of mycobacteria at a genomic level. The Dra I profiles allow the differentiation and precise identification of the BCG Pasteur, Glaxo, Russian and Japanese strains. 相似文献
978.
本文研究了红藻梅膜(Halymenia sinensis),绿藻孔石莼(Ulva pertusa),褐藻裙带(Underia pinnatifida)及蓝藻钝顶螺旋藻(Spir~dulina platensis)的DCMU增益荧光比率(F_D/F_N)。其中海膜的比率最高(3.9),石莼及螺旋藻次之(2.5和2.8),裙带(采自夏季)的比率最低(1.7)。脱水及热处理下和藻体老化时,F)D/F_N值显著下降。在实验室条件下分批培养的两种赤潮藻海洋原甲藻(Prorocentrum micans)和微小角毛藻(Chaetocersa minutissmus),其增殖过程中最大增益荧光比率较最大增殖速率出现早,这一结果为赤潮的预报提供了依据。 相似文献
979.
Abstract. A methodology for the morphological analysis of herbaceous communities is presented, together with an example of its application in montane grasslands in the province of Córdoba (Argentina) subject to grazing and burning. The method, based on multivariate ordination and classification techniques, enabled the detection of morphological changes at three levels in response to disturbance: (a) characterization of the spatial structure of the vegetation; (b) identification of morphological plant groups; and (c) quantification of morphological shifts among different individuals of a single species. The architecture of the vegetation changed toward a progressive miniaturization of photosynthetic structures and concentration of biomass close to the ground, as disturbance intensity increased. Six morphological plant groups (modes of response) showing different behaviour in relation to competition for light and pressure from large herbivores were identified. Some species, highly preferred by ungulate grazers, showed high morphological variability among morphs growing in different grazing situations, whereas some others were morphologically uniform. 相似文献
980.
Summary The effect of full sunlight, 60%, or 90% attenuated light on photosynthetic rate, growth, leaf morphology, dry weight allocation patterns, phenology, and tolerance to clipping was examined in the glasshouse for steppe populations of the introduced grass, Bromus tectorum. The net photosynthetic response to light for plants grown in shade was comparable to responses for plants grown in full sunlight. Plants grown in full sunlight produced more biomass, tillers and leaves, and allocated a larger proportion of their total production to roots than plants grown in shade. The accumulation of root and shoot biomass over the first two months of seedling growth was primarily responsible for the larger size at harvest of plants grown in full sunlight. Plants grown under 60% and 90% shade flowered an average of 2 and 6 weeks later, respectively, than plants grown in full sunlight. Regrowth after clipping was greater for plants grown in full sunlight compared to those grown in shade. Even a one-time clipping delayed flowering and seed maturation; the older the individual when leaf area was removed, the greater the delay in its phenology. Repeated removal of leaf area was more frequently fatal for plants in shade than in full sunlight. For plants originally grown in full sunlight, regrowth in the dark was greater than for shaded plants and was more closely correlated to non-flowering tiller number than to plant size. This correlation suggests that etiolated regrowth is more likely regulated by the number of functional meristems than by differences in the size of carbohydrate pools. Thus, shading reduces the rate of growth, number of tillers, and ability to replace leaf area lost to herbivory for B. tectorum. These responses, in turn, intensify the effect of competition and defoliation for this grass in forests. B. tectorum is largely restricted to forest gaps at least in part because of its inability to acclimate photosynthetically, the influence of shade on resource allocation, and the role of herbivory in exacerbating these effects. 相似文献