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The growth response ofCalopogonium caeruleum, a leguminous covercrop in plantation agriculture, to inoculation with two vesicular-arbuscular mycorrhizal (VAM) fungi was
investigated in five phosphorus (P)-deficient soils supplied with various levels of rock phosphate. Significant shoot yield
increases over the uninoculated controls were obtained in most sterilised or unsterilised soils at all applied P levels, although
the inoculant VAM fungi differed in their effectiveness in the soils used. Responses in mycorrhizal root infections, P and
nitrogen (N) concentrations in tops and plant nodulation varied. The results are discussed in relation to the edaphic environment
of the mycorrhizal association. 相似文献
24.
F. Gasse 《Hydrobiologia》1987,154(1):127-163
Palaeoenvironments are reconstructed from the diatom flora of Holocene swamp and lacustrine sediments which lie in closed depressions of the Chad basin (Niger).The geological and hydrological setting of the sedimentary profiles investigated is presented in section I. Three types of hydrological environments are considered: depressions which have been connected with L. Chad during the Holocene, small river-fed basins outside of the maximum extension of L. Chad, and depressions which have been mainly supplied by groundwater.Methods used for palaeoecological reconstruction are discussed (section II) on the basis of the present-day distribution of diatom species and communities in the investigated zones. Attention is drawn to the diversity of the habitats in a given waterbody, and on the potential effects of seasonality and water stratification on the composition of diatom assemblages contained in the sediments. Because of the spatial and temporal changes in diatom communities, the sediment may integrate a mixture of communities with different ecological requirements. Thus, mean values of individual ecological variables deduced from a fossil assemblage are not sufficient to characterize a palaeoenvironment.In section III, a classification of the palaeoenvironments is proposed. One attempts to distinguish the different communities contained in the fossil assemblages. The fossil communities are compared to diatom populations living today in the studied zones, or in other African sectors when no regional analogue has been found, and for which ecological conditions are known. This allows environmental characteristics to be inferred from sedimentary profiles. At a given time, the palaeosystems show the same ecological diversity as the modern ones.The main status of the palaeoenvironmental evolution are then drawn for each stratigraphical profile (section IV), for an understanding of their causes. The major climatic tendancies affecting intertropical Africa have been chiefly responsible for the presence or absence of aquatic environments in the closed depressions. Superimposed to that, the diversity and the evolution of the individual palaeoecosystems have been controlled by local topographical and hydrological factors (origin of water, permeability of lake floor. . ). This is a common situation for waterbodies lying in tropical arid and semi-arid zones, and especially for palaeolakes associated to groundwater circulations. Therefore, palaeolimnological data can hardly serve as direct and accurate climatic indicators, if they are not corrected for the effects of local hydrology. 相似文献
25.
Possible causes of high species diversity in tropical Australian freshwater macrobenthic communities 总被引:2,自引:2,他引:0
P.M. Outridge 《Hydrobiologia》1987,150(2):95-107
A total of 133 benthic macroinvertebrate species was recorded in four permanent freshwater lagoons (billabongs) and a stream riffle in the Magela Creek catchment, Northern Territory, Australia. 101 species were lentic in occurrence. Each billabong supported at least as many species as larger tropical and Australian temperate lakes, and was an exception to the species-poor status of Australian lentic macrobenthic communities. > 98% of the total benthic biomass was contributed by a mussel species; the remaining species' combined standing crop was an order of magnitude lower than in other lentic systems, further highlighting the diversity of the Magela benthos. Rarefaction (removal of organisms) and predictable environmental heterogeneity, both related to monsoonal variations in flow and water quality, were probably important determinants of the high diversity of these communities. 相似文献
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R. Chima Wokocha 《Plant and Soil》1988,106(1):146-148
Populations of viable sclerotia ofSclerotium rolfsii were highest in soil in a field in which tomato was planted for three successive years before sampling and in one in which
tomato followed groundnut in the 2 years prior to this study. The lowest sclerotial numbers were recorded in fields in which
groundnut followed maize or in which maize or sorghum was the last crop before sampling. 相似文献
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Endoparasitic copepods are very numerous in Indo-West Pacific corals. In West Indian corals they were thought to be absent, but recent studies have shown that a varied endoparasitic copepod fauna exists as well. Striking is the taxonomic composition of the coral-inhabiting copepods:In the Indo-West Pacific Lichomolgidae and Xarifiidae are the dominant families, both are absent in the West Indies. On the other hand, Corallovexiidae and Asterocheridae dominate in the West Indies; the former family is absent and the latter is apparently rare and not very diversified in the Indo-West Pacific. 相似文献
30.
The migratory movements of reproductive potamodromus fish established in man-made tropical lakes in the dry zone of Sri Lanka were determined. It was shown that the nine indigenous riverine species do not spawn in these lakes but move into the upstream channels when sexually mature. The pattern of upstream movement was found to be species-specific although most species showed a diurnal periodicity. It is suggested that the development of totally lacustrine forms of riverine species is very unlikely to occur in the man-made lakes of Sri Lanka because of their relatively short duration time. 相似文献