Reconstruction of late Quaternary marine and terrestrial environmental conditions of Northwest Africa and Southeast Australia A multiple organic proxy study using marine sediments

NW Africa and SE Australia are regions which are particularly vulnerable to climate change. In this thesis, organic proxies are used from marine sediment cores to reconstruct past environmental conditions from these areas. In sediments from NW Africa, the UK'37 showed an efficient proxy for sea surface temperature (SST) reconstruction, while the TEXH86 reconstructed thermocline temperatures. The UK'37 and TEXH86 records for the last 192 ka showed that periods of reduced AMOC coincide with a reduction in the vertical temperature gradient. Thus, variations in AMOC strength is a driver of the thermocline structure in the tropical Atlantic. Three independent organic proxies (UK’37,TEXH86 and LDI) were used to reconstruct SSTs for the last 135 ka in sediments from offshore SE Australia. Comparison with SST estimates based on foraminiferal assemblages shows that LDI temperatures compared well with the temperature of the warmest month, TEXH86 with the temperature of the coolest month and UK’37 with mean annual temperature. Thus, the application of these 3 proxies together at this area enables the reconstruction of SST variations from different seasons. Accumulation rates and concentrations of biomarkers from marine plankton classes were used to examine the changes in productivity at the above mentioned sites during the late Quaternary. In NW Africa, a positive correlation was observed between TOC content, productivity proxies (for dinoflagellates, eustigmatophytes, haptophytes) and the sedimentary Fe, in particular during periods of high aridity on the continent. Thus, the productivity in this area is considerably influenced by the fertilization effect of the Sahara dust, while in SE Australia, Proboscia diatom productivity seems to be controlled by the transport of silicic acid to this area as increases in its productivity matched increased diatom productivity observed at some sites of the tropical equatorial Pacific. To assess changes in the vegetation of NW Africa and SE Australia, the d13C of the n-alkanes from plant leaf waxes were analysed. Sediments from the NW Africa reveal three periods (early Holocene, 50–45 and 120–110 ka) during the past 192 ka when the central Sahara/Sahel contained a higher percentage of C3 plants, indicating wetter conditions than at present. A remarkably close correlation between d13C of benthic foraminifera and n-alkanes indicates a connection between variability in AMOC strength and vegetation type in the Sahara/Sahel region. The n-alkane d13C record from SE Australia reveals an extensive period (68-31ka) of high C4 plant abundance that is punctuated by a sharp increase in C3 vegetation at ~43 ka. This sharp increase in C3 vegetation lasts ~5 ka and is characterized by increased levels of biomass burning. Thus, this vegetation change was likely caused by increased burning events and/or by reduced herbivory as it follows the main period of the late Quaternary megafauna extinction in Australia. This thesis demonstrates the benefit of applying multiple organic proxies on marine sediments to assess marine and terrestrial paleoenvironmental changes and it has thereby provided new insights in the cause and effect of environmental changes in marine and continental areas of NW Africa and SE Australia

Peat properties, dominant vegetation type and microbial community structure in a tropical peatland

Tropical peatlands are an important carbon store and source of greenhouse gases, but the microbial component, particularly community structure, remains poorly understood. While microbial communities vary between tropical peatland land uses, and with biogeochemical gradients, it is unclear if their structure varies at smaller spatial scales as has been established for a variety of peat properties. We assessed the abundances of PLFAs and GDGTs, two membrane spanning lipid biomarkers in bacteria and fungi, and bacteria and archaea, respectively, to characterise peat microbial communities under two dominant and contrasting plant species, Campnosperma panamensis (a broadleaved evergreen tree), and Raphia taedigera (a canopy palm), in a Panamanian tropical peatland. The plant communities supported similar microbial communities dominated by Gram negative bacteria (38.9–39.8%), with smaller but significant fungal and archaeal communities. The abundance of specific microbial groups, as well as the ratio of caldarchaeol:crenarchaeol, isoGDGT: brGDGTs and fungi:bacteria were linearly related to gravimetric moisture content, redox potential, pH and organic matter content indicating their role in regulating microbial community structure. These results suggest that tropical peatlands can exhibit significant variability in microbial community abundance even at small spatial scales, driven by both peat botanical origin and localised differences in specific peat properties

Sward structure and livestock performance in guinea grass cv: Tanzania pastures managed by rotational stocking strategies

Grazing strategy is a key element in the determination of sward structure, herbage nutritive value and animal performance. We aimed to compare the herbage characteristics and performance of livestock in pastures of Panicum maximum cv. Tanzania managed, using two rotational stocking strategies, which provided either a fixed-length rest period (FRP) of 35 days in the spring and fall and 30 days in the summer, or a variable-length rest period (VRP), determined by the time required for the canopy to achieve 70 cm in height. The pastures were evaluated in the pregrazing condition for forage mass (FM); leaf (LP), stem (SP) and dead matter (DP) percentages; and nutritive value (NV). The animals were weighed every 28 days. Pastures managed with the FRPs exhibited greater FMs, SPs and DPs and lower LPs and NVs than those managed with the VRPs. The average daily livestock weight gain was greater during the spring and summer for the VRP than for the FRP pastures, resulting in an average animal weight gain per area of 990 and 860 kg ha−¹ wet period−¹ for the pastures managed with the VRPs and FRPs, respectively. Thus, pasture rest periods that were maintained after the sward reached 70 cm in height reduced the animal performance on Tanzania guinea grass

Application of Comet assay to assess the effects of white bean meal on DNA of human lymphocytes

This study was conducted to evaluate the potential induction of genotoxic effects of white bean flour using the Comet assay. The test was conducted with human lymphocytes present in whole blood immediately after collection, by incubation with white bean flour in three concentrations (3.92, 9.52 and 18.18 mg/mL) at 37 ºC for 4 h followed by preparation of slides. Samples were considered positive (above 20% damage) when the damage observed to cellular DNA was higher than the negative control. No genotoxic potential was found at the doses tested. However, it would be premature to suggest absence of risk to human health of DNA damage since the exposure of cells to the extract was restricted to four hours rather than a whole cell cycle. Additionally, further information on toxicology should be obtained in future studies.Este estudo foi realizado para avaliar o potencial de indução de efeitos genotóxicos da farinha de feijão branco utilizando o teste do Cometa. O ensaio foi realizado com linfócitos humanos presentes no sangue imediatamente após a coleta, por incubação com farinha de feijão branco em três concentrações (3,92, 9,52 e 18,18 mg/mL) a 37 ºC por 4 h, seguida de preparação das lâminas. As amostras foram consideradas positivas (acima de 20% de dano), quando os danos observados no DNA celular foram maiores do que o controle negativo. Verificou-se que as doses testadas não mostraram potencial genotóxico. No entanto, seria prematuro fazer recomendações sobre o padrão de riscos para a saúde humana resultantes de danos ao DNA já que exposição das células ao extrato foi restrito ao período de quatro horas e não durante um ciclo celular completo. Além disso, outras informações sobre a toxicologia devem ser obtidas no futuro