IThemba Laboratories

Johannesburg, South Africa

IThemba Laboratories

Johannesburg, South Africa

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Patrut A.,Babes - Bolyai University | Woodborne S.,IThemba Laboratories | Von Reden K.F.,Woods Hole Oceanographic Institution | Hall G.,University of Pretoria | And 3 more authors.
PLoS ONE | Year: 2015

The article reports the radiocarbon investigation results of the Lebombo Eco Trail tree, a representative African baobab from Mozambique. Several wood samples collected from the large inner cavity and from the outer part of the tree were investigated by AMS radiocarbon dating. According to dating results, the age values of all samples increase from the sampling point with the distance into the wood. For samples collected from the cavity walls, the increase of age values with the distance into the wood (up to a point of maximum age) represents a major anomaly. The only realistic explanation for this anomaly is that such inner cavities are, in fact, natural empty spaces between several fused stems disposed in a ringshaped structure. We named them false cavities. Several important differences between normal cavities and false cavities are presented. Eventually, we dated other African baobabs with false inner cavities. We found that this new architecture enables baobabs to reach large sizes and old ages. The radiocarbon date of the oldest sample was 1425 ± 24 BP, which corresponds to a calibrated age of 1355 ± 15 yr. The dating results also show that the Lebombo baobab consists of five fused stems, with ages between 900 and 1400 years; these five stems build the complete ring. The ring and the false cavity closed 800- 900 years ago. The results also indicate that the stems stopped growing toward the false cavity over the past 500 years. © 2015 Patrut et al.


Murray I.W.,University of Witwatersrand | Lease H.M.,University of Witwatersrand | Lease H.M.,Whitman College | Hetem R.S.,University of Witwatersrand | And 4 more authors.
Integrative Zoology | Year: 2016

We used stable isotopes of carbon and nitrogen to study the trophic niche of two species of insectivorous lizards, the Husab sand lizard Pedioplanis husabensis and Bradfield's Namib day gecko living sympatrically in the Namib Desert. We measured the δ13C and δ15N ratios in lizard blood tissues with different turnover times (whole blood, red blood cells and plasma) to investigate lizard diet in different seasons. We also measured the δ13C and δ15N ratios in available arthropod prey and plant tissues on the site, to identify the avenues of nutrient movement between lizards and their prey. Through the use of stable isotope mixing models, we found that the two lizard species relied on a largely non-overlapping but seasonally variable array of arthropods: P. husabensis primarily fed on termites, beetles and wasps, while R. bradfieldi fed mainly on ants, wasps and hemipterans. Nutrients originating from C3 plants were proportionally higher for R. bradfieldi than for P. husabensis during autumn and late autumn/early winter, although not summer. Contrary to the few available data estimating the trophic transfer of nutrients in ectotherms in mixed C3 and C4/crassulacean acid metabolism (CAM) plant landscapes, we found that our lizard species primarily acquired nutrients that originated from C4/CAM plants. This work adds an important dimension to the general lack of studies using stable isotope analyses to estimate lizard niche partitioning and resource use. © 2015 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.


Priyadarshini K.V.R.,Wageningen University | Prins H.H.T.,Wageningen University | de Bie S.,Wageningen University | Heitkonig I.M.A.,Wageningen University | And 5 more authors.
Oecologia | Year: 2014

A key question in savanna ecology is how trees and grasses coexist under N limitation. We used N stable isotopes and N content to study N source partitioning across seasons from trees and associated grasses in a semi-arid savanna. We also used 15N tracer additions to investigate possible redistribution of N by trees to grasses. Foliar stable N isotope ratio (δ15N) values were consistent with trees and grasses using mycorrhiza-supplied N in all seasons except in the wet season when they switched to microbially fixed N. The dependence of trees and grasses on mineralized soil N seemed highly unlikely based on seasonal variation in mineralization rates in the Kruger Park region. Remarkably, foliar δ15N values were similar for all three tree species differing in the potential for N fixation through nodulation. The tracer experiment showed that N was redistributed by trees to understory grasses in all seasons. Our results suggest that the redistribution of N from trees to grasses and uptake of N was independent of water redistribution. Although there is overlap of N sources between trees and grasses, dependence on biological sources of N coupled with redistribution of subsoil N by trees may contribute to the coexistence of trees and grasses in semi-arid savannas. © 2013 Springer-Verlag Berlin Heidelberg.


Patrut A.,Babes - Bolyai University | Woodborne S.,IThemba Laboratories | Patrut R.T.,Babes - Bolyai University | Hall G.,University of Pretoria | And 4 more authors.
Studia Universitatis Babes-Bolyai Chemia | Year: 2015

The paper discloses the radiocarbon investigation results of the Luna tree, a representative African baobab from Venetia Limpopo Nature Reserve, South Africa. Several wood samples collected from deep incisions in the trunk were investigated by AMS (accelerator mass spectrometry) radiocarbon dating. The age sequence of segments extracted from the oldest sample demonstrates that ages increase with the distance into the wood up to a point of maximum age, after which ages decrease toward the sample end. This anomaly is typical for multi-stemmed baobabs, having a closed ring-shaped structure with a false cavity inside. Dating results reveal that each of the two large fused units, which build the Luna tree, consist of such a closed ring. The two closed rings include two interconnected false inner cavities. False cavities are empty spaces between fused stems that were never filled with wood. We named this baobab architecture, which has a very high symmetry, double closed ring-shaped structure with two false cavities. The new architecture, which is very uncommon, enables baobabs to reach large sizes and very old ages. The radiocarbon date of the oldest sample segment was 1507 ± 22 BP, which corresponds to a calibrated age of 1405 ± 20 yr. We estimate that the oldest part of Luna tree has an age of 1600 ± 100 yr. By these results, the Luna tree becomes the fourth oldest African baobab with accurate dating results. © 2015, Universitatea Babes-Bolyai, Catedra de Filosofie Sistematica. All rights reserved.


Dabrowski J.,University of Pretoria | Dabrowski J.,South African Council for Scientific and Industrial Research | Hall G.,University of Pretoria | Lubcker N.,University of Pretoria | And 4 more authors.
Freshwater Biology | Year: 2014

Summary: Pansteatitis (yellow fat disease) is ubiquitous in the free-ranging population of Oreochromis mossambicus from Loskop Reservoir (LR), South Africa. The disease is nutritionally mediated and associated with a diet high in polyunsaturated or rancid fats, frequently of fish origin. While piscivory has never been reported in dietary studies of O. mossambicus in their native range, their opportunistic and omnivorous feeding habits mean that piscivory cannot be ruled out as a cause of the disease. The diet of O. mossambicus from LR (n = 91) was compared with a population from Flag Boshielo Reservoir (FBR; n = 81) located <100 km downstream, where no pansteatitis occurs. The stomach contents and stable isotope signatures (δ15N and δ13C) of fish and food sources were evaluated across four seasons. Isotope signatures were also compared over various time scales from historic samples and mortalities collected from LR. There was no evidence of piscivorous feeding behaviour in fish from either location or from historic LR samples. The results of the stable isotope analysis in R mixing model and stomach contents analysis showed that the dinoflagellate, Ceratium hirundinella, was the dominant food source followed by zooplankton, detritus and Microcystis aeruginosa in LR. The diet of fish from FBR was less diverse than fish from LR and was dominated by sediment and detritus. The distinguishing feature of the dietary comparison between reservoirs was the abundance of planktonic food items dominated by C. hirundinella in the diet of fish from LR. The lack of evidence for piscivory among O. mossambicus from LR suggests that the classic aetiology of pansteatitis does not apply. This highlights the need to further explore direct (environmental exposure to pollutants) and indirect (dietary exposure) links to pansteatitis. This study identified the major dietary constituents for O. mossambicus, which enables future research to focus on their nutritional and chemical composition. © 2014 John Wiley & Sons Ltd.


Priyadarshini K.V.R.,Wageningen University | de Bie S.,Wageningen University | Heitkonig I.M.A.,Wageningen University | Woodborne S.,IThemba Laboratories | And 3 more authors.
Journal of Arid Environments | Year: 2016

Savannas support mixed tree-grass communities and interactions between these are typically viewed as being competitive based on studies that focused on grass aboveground production. However, an important plant response to competition and resource limitation is an increase in root reserves. We investigated root characteristics of perennial grasses in the presence and absence of trees as a proxy of competition in South African savannas in three sites that differed in rainfall. We based our study on the hypothesis that competition from trees and water limitation will result in increased storage in roots of grasses under trees. Results indicate no significant effect of variation in rainfall of the different study locations on root characteristics of grasses. Furthermore, trees did not significantly influence most grass root characteristics that we measured. The only exception was nitrogen-content that showed an increase with rainfall and tree presence through potentially higher mineralization rates and nitrogen availability in the under-tree canopy environment. As the study sites are in the drier rainfall range in South Africa, it is likely that trees and grasses in these dry savannas may have a positive relationship conforming to the stress-gradient hypothesis. Alternatively, grasses and trees may be using complementary water and nutritional resources. © 2015 Elsevier Ltd.


Gunnlaugsson H.P.,University of Aarhus | Molholt T.E.,University of Iceland | Mantovan R.,CNR Institute for Microelectronics and Microsystems | Masenda H.,University of Witwatersrand | And 14 more authors.
Applied Physics Letters | Year: 2010

Prompted by the generally poor understanding of the nature of magnetic phenomena in 3d -metal doped ZnO, we have undertaken on-line F 57 e Mössbauer spectroscopy on ZnO single crystals in an external magnetic field of 0.6 T, following the implantation of radioactive M 57 n ions at room temperature. The Mössbauer spectra of the dilute Fe impurities are dominated by sextets whose angular dependence rules out an ordered magnetic state (which had been previously proposed) but are well accounted for on the basis of Fe3+ paramagnetic centers on substitutional Zn sites with unusually long relaxation times (>20 ns). © 2010 American Institute of Physics.


Priyadarshini K.V.R.,Wageningen University | Prins H.H.T.,Wageningen University | de Bie S.,Wageningen University | Heitkonig I.M.A.,Wageningen University | And 6 more authors.
Ecohydrology | Year: 2016

Savanna vegetation is characterized by tree-grass co-existence that can experience intense water limitation, yet the water relations of these savanna plants are poorly understood. We examined the water sources for trees and grasses in different seasons and investigated the importance of hydraulic redistribution in three tree species inhabiting a semi-arid savanna in South Africa. We used natural variation in H and O stable isotope composition of source waters to identify the principal water sources for these plants. We conducted an experiment by labelling deep-soil (2.5-m depth) with a deuterium tracer. Seasonal differences in the stable isotope composition of water in trees and grasses indicated that there was water-source use partitioning as well as overlap. Trees and grasses used water from the topsoil after rainfall indicating overlap of water-source use. All tree species shifted to groundwater or subsoil water use when there was no water in the topsoil indicating partitioning of water use. Grasses always used water from the topsoil. The seasonal changes in water-source use by trees and grasses indicated possible shifts in tree-grass interactions during different periods of the year. The tracer experiment confirmed hydraulic redistribution in all the three tree species and water transfer to grasses via the topsoil. However, this occurred only in the dry season. Our observations and experimental results indicate the potential for facilitation effects by trees to their understory grasses and show that dry season hydraulic redistribution from trees to grasses could be an important facilitative mechanism maintaining tree-grass co-existence in savannas. © 2015 John Wiley & Sons, Ltd.


PubMed | University of Witwatersrand and iThemba Laboratories
Type: Journal Article | Journal: Integrative zoology | Year: 2016

We used stable isotopes of carbon and nitrogen to study the trophic niche of two species of insectivorous lizards, the Husab sand lizard Pedioplanis husabensis and Bradfields Namib day gecko living sympatrically in the Namib Desert. We measured the (13) C and (15) N ratios in lizard blood tissues with different turnover times (whole blood, red blood cells and plasma) to investigate lizard diet in different seasons. We also measured the (13) C and (15) N ratios in available arthropod prey and plant tissues on the site, to identify the avenues of nutrient movement between lizards and their prey. Through the use of stable isotope mixing models, we found that the two lizard species relied on a largely non-overlapping but seasonally variable array of arthropods: P. husabensis primarily fed on termites, beetles and wasps, while R. bradfieldi fed mainly on ants, wasps and hemipterans. Nutrients originating from C3 plants were proportionally higher for R. bradfieldi than for P. husabensis during autumn and late autumn/early winter, although not summer. Contrary to the few available data estimating the trophic transfer of nutrients in ectotherms in mixed C3 and C4 /crassulacean acid metabolism (CAM) plant landscapes, we found that our lizard species primarily acquired nutrients that originated from C4 /CAM plants. This work adds an important dimension to the general lack of studies using stable isotope analyses to estimate lizard niche partitioning and resource use.

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