Botany
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Item Soil aeration as an ecological factor governing mangrove zonation(Springer-Netherlands, 1993) Jayasekera, R.; Lieth, H.The growth of both Rhizophora mangle L. and Rhizophora mucronata Lamk. in saline sand was highly promoted by flooded, reducing conditions in comparison to drained, aerobic conditions, showing the strong tolerance of Rhizophora seedlings to waterlogging and salinity. Under well-drained conditions, both shoot and root systems of the plants showed strongly retarded and reduced growth and a profound inverse proportionality was also found between root growth and pot volume; roots of both species were distorted and showed lack of capillary rootlets. The morphology of the root systems was greatly affected by the culture conditions providing evidence for the ecological adaptability of the Rhizophora root system to a wide variety of environmental conditions. The results obtained are in good agreement with their position in the lower, flooded zone of natural mangrove communities.Item Interelement correlations in the mangrove, Rhizophora mangle L.(Springer-Netherlands, 1993) Jayasekera, R.; Lieth, H.Assuming linear relationships between elements, some significant interelement relationships were detected in Rhizophora mangle grown over a salinity gradient. Sodium (Na) had a clear antagonistic effect on the uptake of potassium (K), whereas the uptake of chromium (Cr) and arsenic (As) seemed to be stimulated by sodium ions. A positive relationship between leaf carbon content and sodium concentration was also found. A significant negative correlation was found between the chemically related two elements, rubidium (Rb) and caesium (Cs). Owing to the competition with the absorption of K+ and NH+ 4 a negative relationship between nitrogen (N) and potassium (K) was found.Item Effect of available rooting volume on seedling growth(Springer-Netherlands, 1993) Jayasekera, R.; Lieth, H.During the early establishment phase of Rhizophora mangle L. seedlings, a consistent positive relationship between available soil volume (varying from 2-91) and growth rate of Rhizophora manglehas been established under greenhouse conditions. As soil volume increased, root systems were larger and consistently less dense. From the results obtained it may be concluded that for optimal growth of Rhizophora mangle seedlings, the volume of soil per plant should approach that volume associated with the growth of the plants in natural habitats. Root volume appears to be a very significant index of plant growth, even under saline, flooded conditions.Item Implementation of specimen banking concepts in developing countries: First trial - Sri Lanka(Elsevier, 1993) Jayasekera, R.; Rossbach, M.The necessity to establish a small scale Environmental Specimen Bank projects in tropical countries is stressed. An example from Sri Lanka demonstrates the needs, the benefits and the prospects of such an integrated research project.Item Pattern of distribution of selected trace elements in the marine brown alga, Sargassum filipendula Ag. from Sri Lanka(Kluwer Academic Publishers, 1994) Jayasekera, R.Baseline concentrations together with biological variations of 29 trace elements (Ag, As, Au, Ba, Br, Cd, Ce, Co, Cr, Cs, Eu, Fe, Hf, I, Mn, Mo, Ni, Pb, Rb, Sb, Sc, Se, Sm, Sr, Tb, Th, Yb, Zn and Zr) were investigated in the brown alga, Sargassum filipendula collected from the western coast of Sri Lanka. Several elements (Co, Cr, Fe, Hf, Ni, Sc, Se, Th, Zr and the rare earth elements) were found to be enriched in S. filipendula compared to NIES No. 9 Sargasso reference material. Concentration of strontium in S. filipendula was highest at all sites. Chemical abundance of the rare earth elements decreased approximately linearly with increasing atomic numbers. The pattern of elemental distribution appears to be due to the fact that S. filipendula seems capable of concentrating high levels of trace elements under conditions of their very low availability in sea water. Concentration factors for elements in S. filipendula lie in a higher range compared with those reported in the literaure for brown algae.Item Sampling of tropical terrestrial plants with particular reference to the determination of trace elements(VCH Publisher, 1994) Jayasekera, R.Item Seasonal changes in organic carbon content of leaves of deciduous trees(Elsevier, 1991) Jayasekera, R.; Schleser, G.H.Changes in organic carbon content were investigated during the course of one growing season in the leaves of beech (Fagus sylvaticaL.) and oak (Quercus robur L.). Considerable alterations in leaf carbon content were found not only during the course of the growing season, but also as a function of tree height. Until about August, leaf carbon content of oak gradually increased and then showed a decline as the leaves yellowed in October. In beech sun leaves there was a gradual increase in organic carbon content with increasing foliage age, whereas shade leaves showed the opposite trend. The results demonstrate that leaf carbon content may vary during leaf ontogenesis, and that the character of ontogenetic changes in carbon content depends not only on plant species but also on canopy position.Item Multi-laboratory chemical characterization of ecological samples(Springer-Verlag, 1989) Jayasekera, R.; Markert, B.The influence of high concentrations of sodium (Na), chlorine (Cl) and bromine (Br) on the analytical results obtained by means of several modern analytical methods by different laboratories was investigated. The results obtained for the halophytic plants, Aster tripolium and Rhizophora mangle, were compared with that of NBS-Citrus leaves (NBS 1572). With a few outliers no considerable “interference effects” from Na, Cl and Br on the results of other elements were found.Item Background levels of heavy metals in plants of different taxonomic groups from a montane rain forest in Sri Lanka(Kluwer Academic Publishers, 1996) Jayasekera, R.; Rossbach, M.An undisturbed natural reserve area iocated in a tropical montane rain forest at about 1800 m altitude in Sri Lanka served as a study site to investigate and assess the natural background concentration levels of As, Cd, Co, Cu, Ni, Pb and Zn in plants representing different taxonomic groups (divisions) in the plant kingdom. The plants selected were: the lichen,Usnea barbata (old man's beard);Pogonatum sp. (a moss);Lycopodium selago (epiphytic lycopod);Polypodium lanceolatum (epiphytic fern);Bulbophyllum elliae (epiphytic orchid) andActinodaphne ambigua(dicotyledonous large tree). Degree of homogeneity with respect to Cd, Cu, Pb and Zn in homogenised materials of all samples were within acceptable limits, whereasPogonatum sp. showed the highest degree of homogeneity for Pb. In addition to confirming extremely low levels of heavy metals in all plant species, the survey also found that generally the primitive plants,UsneaandPogonatum appear to have a greater tendency to accumulate As, Cd, Co and Pb; in particular,U. barbata appears to be an efficient accumulator for those heavy metals, suggesting its potential use in environmental studies.Actinodaphne ambigua was found to have a specific accumulating ability for nickel. Surface cleaning of theA. ambigua leaves resulted in a substantial decrease in the foliar contents of Cd, Ni, Pb and Zn. Variations in heavy metal contents observed in different plant genera are discussed in terms of their habits and place of growth in the forest. It is anticipated that the background levels presented in this paper from a remote, unpolluted tropical ecosystem will provide useful reference data for comparative environmental studies.Item Interelement relationships in leaves of tropical montane trees(Kluwer Academic Publishers, 1993) Jayasekera, R.Chemical concentrations in leaves are reported for 14 elements in 6 tree species of a montane rain forest in Sri Lanka. The plant taxa varied greatly in chemistry and a few taxa appeared to concentrate several elements in high amounts. The chemical variability among taxonomic units was examined by comparing element-by-element concentration ratios in leaves. Several species seemed to have typical patterns of concentration ratios for certain elements and the interelement relationships of different species seemed to be repeated across varying habitat conditions.