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Adriana García 《Hydrobiologia》1993,267(1-3):143-154
Only recently have extant Lamprothamnium species been reported from the American continent. L. succinctum (A. Br. in Asch.) R. D. W. was found in Lago Titicaca, Bolivia and L. haesseliae Dont. en Laguna Luro and Laguna La Salada, Argentina.Fossil gyrogonites of L. succinctum and L. haesseliae, however, are here reported to be widely distributed in Quaternary sediments of Argentina, associated with other charophytes, ostracods and foraminiferans. Localities include Laguna del Siasgo, Laguna Salada Grande, Laguna Mar Chiquita, Laguna La Amarga and Salina del Bebedero.
Lamprothamnium is a genus that prefers shallow, alkaline, hyposaline to mesosaline environments. Analysis of the characteristics of Laguna La Salada contributes information on the factors that influence the distribution of the genus.The morphology characteristics of the gyrogonites and oospores of L. haesseliae and the gyrogonites of L. succinctum are described. The use of Lamprothamnium as a biomarker and its application in the reconstruction of Quaternary saline environments are also discussed. 相似文献
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The effects of salinity on the reproduction of coastal submerged macrophyte species were studied on samples of communities from six seasonal marshes in two outdoor experiments performed in autumn and in spring. The submerged macrophyte communities were submitted to five different salinity levels (0, 1, 2, 4 and 6 g/1 Cl?1). In a companion paper (Grillas, van Wijck & Bonis 1993) three groups of species were distinguished on the basis of their biomass production over the salinity range 0 to 6 g/1 Cl?1: (1) glycophytes (non-salt-tolerant species), (2) salt-tolerant species and (3) halo-phytes. This part of the study describes the impact of salinity on the reproduction of the individual species during the two experiments. The species differ in their capacity to reproduce in the autumn; only Zannichelliapedunculata and Tolypella hispánica were able to produce fruits in that season. For all species reproduction was greater in spring and strongly correlated with biomass, except for Chara canescens. Differences in reproductive effort over the salinity range amplified the halophytic nature of Ruppia marítima and Chara canescens and the intolerance of Callitriche truncata and Chara contraria. For the other species, reproductive effort did not differ significantly over the salinity range. Regarding the effect of salinity on biomass and reproductive effort of individual species, there were large differences in the total weight of propagules produced at the community level and in the relative contribution of individual species. The resulting quantitative changes in the species composition of the seed bank could affect the structure of the communities by their effects on the establishment and survival of species populations. 相似文献
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The relationship between adenine-nucleotide levels and metabolism-dependent membrane potential was studied in cells of Nitellopsis obtusa. Effects of ADP and AMP in the presence of ATP on electrogenic pump activity were measured in the dark, using the continuous perfusion method. Both ADP and AMP acte as competitive inhibitors for ATP, the Ki value for either compound being about 0.4 mM. The role of ADP and AMP as regulating factors for the electrogenic pump was investigated under various metabolic conditions. Application of N2 gas in the dark caused a significant membrane depolarization amounting to 90 mV, but cytoplasmic streaming and membrane excitability were not affected. Under anoxia, the ATP level decreased from 1.6 to 0.5 mM; ADP increased but only slightly, and AMP increased greatly. However, the time course of changes in the adenine nucleotides was not concurrent with that of the membrane-potential changes, thus, the adenine-nucleotide level changes cannot fully account for the N2-elicited depolarization. Under light, although the membrane hyperpolarized, no significant changes in the adenine-nucleotide levels were observed. Therefore, the light-induced membrane hyperpolarization cannot be explained solely by changes in adenine-nucleotide levels.Abbreviations APW
artificial pond water
- Em
membrane potential
- Rm
membrane resistance 相似文献
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Intercellular communication in Chara: factors affecting transnodal electrical resistance and solute fluxes 总被引:2,自引:1,他引:1
The permeability of plasmodesmata in the nodal complex of branch cells of Chara corallina was examined by measuring both the transnodal electrical resistance and transnodal fluxes of 36CI and 14C-buty-rate. Under normal circumstances, the resistance across the node was low, but increased rapidly in response to metabolic inhibition, pressure gradients across the node or excision of one of the cells. For each of these treatments, there was a substantial reduction in solute transport between the cells. Acidification of the cytoplasm by weak acids or alkalinization by amines did not affect either the electrical resistance or the flux of solutes through the node between whorl cells. The transnodal resistance was significantly higher in older cell pairs, but was unaffected by large transnodal voltage differences or by the passage of action potentials. There was no evidence that short-term increases in cytoplasmic calcium have any effect on plasmodesmatal permeability. 相似文献
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Evolutionary patterns of Clavatoraceae during the Malm and the Lower Cretaceous can be understood by considering how palaeoecological constraints of these charophytes were affected by palaeoenvironmental change. Speciation of Clavatoraceae reached maxima in the Tithonian and especially in the Lower Barremian, coinciding with an important areal extension and environmental diversification of freshwater swamps. Extinction reached a peak in the Upper Barremian, coinciding with the marine flooding of freshwater environments in Mesogea, and continued through the Aptian and Albian due to substitution of carbonatic freshwater swamps by terrigenous deltaic environments and probably by development of highly competitive aquatic flora of angiosperms. Anagenetic change within species attained maxima during the Berriasian and Lower Barremian, when freshwater environments became extensively developed. Absence of change (stasis) was marked during the Valanginian and Hauterivian, in a geological context of environmental stability and areal reduction of the freshwater environments. 相似文献
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First discovery of the charophycean green alga Lychnothamnus barbatus (Charophyceae) extant in the New World 下载免费PDF全文
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James M. Graham Carole A. Lembi Holly L. Adrian David F. Spencer 《Journal of phycology》1995,31(4):531-540
Spirogyra Link (1820) is an anabranched filamentous green alga that forms free-floating mats in shallow waters. It occurs widely in static waters such as ponds and ditches, sheltered littoral areas of lakes, and stow-flowing streams. Field observations of its seasonal distribution suggest that the 70-μm-wide filament form of Spirogyra should have a cool temperature and high irradiance optimum for net photosynthesis. Measurements of net photosynthesis and respiration were marie at 58 combinations of tight and temperature in a controlled environment facility. Optimum conditions were 25°C and 1500 μmol photons m−2 s−1 , at which net photosynthesis averaged 75.7 mg O2 gdm−1 h−1 . Net photosynthesis was positive at temperatures from 5° to 35°C at most irradiances except at combinations of extremely low irradiances and high temperatures (7 and 23 μmol photons m−2 s−1 at 30°C and 7, 23, and 35 μmol photons m−2 s−1 at 35°C). Respiration rates increased with both temperature and prior irradiance. Light-enhanced respiration rates were significantly greater than dark respiration rates following irradiances of 750 μmol photons m−2 s−1 or greater. Polynomials were fitted to the data to generate response surfaces; such response surfaces can be used to represent net photosynthesis and respiration in ecological models. The data indicate that the alga can tolerate the cool water and high irradiances characteristic of early spring but cannot maintain positive net photosynthesis under conditions of high temperature and low light (e.g. when exposed to self-shading ). 相似文献
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