Botany

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Some aquatic hyphomycetes from Sri Lanka
(Natural Resources, Energy and Science Authority of Sri Lanka, 1984) Gunasekera, S.A.; Rukmani, M.P.R.
δ13C - variations of leaves in forests as an indication of reassimilated CO2 from the soil
(Springer-Verlag, 1985) Schleser, G.H.; Jayasekera, R.
An attempt has been made to evaluate the contribution of soil respired CO2 to the total assimilation of a forest tree, by heeding the 13C-concentrations of CO2 from the free atmosphere and from mineralization processes within the soil respectively. An expression has been derived, according to which the assimilated fraction of CO2 from the soil at a particular height of a tree is given by the δ13C-value of the corresponding leaves, δ13C of atmospheric CO2, δ13C of soil respired CO2 and the physiological state of the leaves expressed as the ratio of total respiration over gross photosynthesis and internal over external CO2-concentration. In the particular case investigated, a δ13C-difference of 5‰ has been determined from bottom to top of a beech tree which results in a CO2 contribution from the soil of about 22% for the lower forest strata, while the total contribution of soil respired CO2 accounts for about 5% of the overall assimilation.
Elemental composition of different plant species
(Journal of Plant Nutrition, 1987) Markert, B.; Jayasekera, R.
Element concentrations in leaves and needles of different plant species (Rhizophora mangle, Astertri‐polium, Vaccinium vitis—idaea and Pinus sylvestris) are presented in the form of element concentration cadasters with reference to their abundance. The concentration cadasters of the two halophytes (Rhizophoramangle and Aster tripolium) show that the elements Na, Cl, Br and Sr occur at high concentrations in halophytes. The changes in chemical abundances of halophytes can be attributed to the extreme habitat conditions, i. e. physiological drought, under which they grow. Certain elements are preferentially accumulated in specific plants, e. g. Mn in Vaccinium vitis‐idaea.
Seasonal changes in potential net photosynthesis of sun and shade leaves of Fagus sylvatica L.
(Elsevier, 1988) Jayasekera, R.; Schleser, G.H.
Sun and shade leaves of the deciduous tree, Fagus sylvatica, were investigated for their potential photosynthetic activity during the course of one growing season. During the initial period of leaf development and expansion, sun leaves exhibited relatively higher photosynthetic rates. After full expansion of leaves, shade leaves had a higher activity in potential net photosynthesis until about the end of August. Low diffusion resistance for CO2/O2 and higher activities of photosystems in shade leaves seem to be the main causes of their higher photosynthetic potential.
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.
Pod yield on winged bean after chemical treatment for choanephora blight disease
(Natural Resources, Energy and Science Authority of Sri Lanka, 1990) Gunasekera, S.A.; Shanthichandra, W.K.N.
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.
Studies on the composition and biodegradation of cane molasses distillery slop of the Sevanagala sugar factory
(Sri Lanka Association for the Advancement of Science, 1991) Chandrasena, G.; Widanapathirana, G.S.
Effect of Sodium chloride (NaCl) salinity on some physiological traits of rice (Oryza sativa L.)
(Sri Lanka Association for the Advancement of Science, 1991) Ranasinghe, A.; Peiris, B.
Floristic composition of the undergrowth at a selected site in Hurulu forest reserve (sigiriya)
(Sri Lanka Association for the Advancement of Science, 1991) Perera, B.M.S.; Solangaarachchi, S.M.
Chemical composition of the mangrove, Rhizophora mangle L.
(Elsevier, 1991) Jayasekera, R.
Enrichment and deposition of selected minerals in mangrove, Rhizophora mangle, plants grown under glasshouse conditions at near-constant salinity were investigated. The results show that R. mangle is capable of concentrating a variety of chemical elements by taking them up from salt water. Mean concentration factors for elements found in R. mangle lie in a higher range compared with those of a glycophyte, Brassica oleracea. Moreover, R. mangle plants seem to have higher affinities for elements such as sodium (Na), chlorine (CI), silicon (Si), cobalt (Co) and cerium (Ce), which may or may not be essential to them.
Elemental concentrations in a tropical montane rain forest in Sri Lanka
(Kluwer Academic Publishers, 1992) Jayasekera, R.
As a preliminary to studies on biogeochemistry of a tropical montane rain forest at about 1800 m altitude in Sri Lanka, the concentrations of 17 chemical elements in different forest compartments, i.e. in leaves of six floristically dominant tree species, undergrowth, litter, and soil at 0–10 cm and 11–60 cm depth were determined. Foliar chemical differences between species were large. Mean leaf water content, mean leaf area per leaf, and specific leaf weight of each species were also determined. Calcium seems to be used in relatively large quantities by these plants. Phosphorus concentration in all compartments was consistently low. A few species investigated appeared to concentrate aluminium and silicon at high amounts. Concentration differences between compartments were significant only for certain elements. Location effect on the concentrations in soil was considerable for most of the elements studied. When studying plant-soil chemical interactions in these forests, species-level concentrations must be taken into account as the species-specific chemical differences are obscured when treated as canopy leaves.
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.
The flavonoids of the genus Lathyrus and a comparison of flavonoid patterns within the tribe vicieae
(Biochemical Systematics and Ecology, 1993) Ranabahu, P.; Harborne, J.B.
A leaf survey of Lathyrus showed that the flavonols kaempferol and quercetin were present in 36 of 38 species representing nine sections of the genus. Six glycosides of each flavonol were characterised. Kaempferol 3-sophoroside-7-glucoside, previously reported in L. vernus, was found in four further species. Other distinctive glycosidic patterns in the genus include the 3-robinobioside, the 3-sophoroside and the 3-lathyroside-7-rhamnoside. The two species surveyed in section Pratensis were different from all the others, in having flavones as well as flavonols and, additionally, in having proanthocyanidins. These differences in leaf flavonoid patterns also extended to the flowers, pods and seeds. Isoflavone accumulation was confirmed in L. montanus but otherwise the genus was depauperate in isoflavones. A comparison of patterns found in Lathyrus with those of Cicer, Lens, Pisum and Vicia indicate that each genus has a distinctive flavonoid profile.
Leaf flavonoid glycosides as chemosystematic characters in Ocimum
(Biochemical Systematics and Ecology, 1993) Grayer, R.J.; Kitea, G.C.; Veitcha, N.C.; Eckerta, M.R.; Marin, P.D.; Senanayake, S.P.; Paton, A.J.
Abstract Thirty-one accessions of nine species belonging to three subgenera of Ocimum (basil, family Lamiaceae) were surveyed for flavonoid glycosides. Substantial infraspecific differences in flavonoid profiles of the leaves were found only in O. americanum, where var. pilosum accumulated the flavone C-glycoside, vicenin-2, which only occurred in trace amounts in var. americanum and was not detected in cv. Sacred. The major flavonoids in var. americanum and cv. Sacred, and also in all other species investigated for subgenusOcimum, were flavonol 3-O-glucosides and 3-O-rutinosides. Many species in subgenus Ocimum also produced the more unusual compound, quercetin 3-O-(6?-O-malonyl)glucoside, and small amounts of flavone O-glycosides. The level of flavonol glycosides produced was reduced significantly in glasshouse-grown plants, but levels of flavone glycosides were unaffected. A single species investigated from subgenusNautochilus, O. lamiifolium, had a different flavonoid glycoside profile, although the major compound was also a flavonol O-glycoside. This was identified as quercetin 3-O-xylosyl(1??2?)galactoside, using NMR spectroscopy. The species investigated from subgenus Gymnocimum, O. tenuiflorum (=O. sanctum), was characterised by the accumulation of flavone O-glycosides. These were isolated, and identified as the 7-O-glucuronides of luteolin and apigenin. Luteolin 5-O-glucoside was found in all nine species of Ocimumstudied, and is considered to be a key character for the genus.
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.
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.
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.
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.
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.