Browsing Research articles (Dept of Biological Sciences) by Author "Bonyongo, M.C."
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Siele, M.P.; Mubyana-John, T.; Bonyongo, M.C. (Global Science Books http://www.globalsciencebooks.com/index.php?page=shop.product_details&category_id=1&flypage=shop.flypage&product_id=5&option=com_virtuemart&Itemid=56&vmcchk=1&Itemid=56, NaN, 2008)[more][less]
Abstract: Soil cover influences soil biological and chemical processes in various ways. The effects of soil cover (bare soil without litter, litter cover, Mopane tree canopy and grass cover) on soil respiration and microbial population at four sites in the Mopane woodland of north western Botswana were investigated. Soil respiration rates were measured using an infrared gas analyzer. Nitrifying bacterial populations were quantified by MPN on ammonium and nitrite calcium carbonate media, oligotrophs on 1% nutrient agar, actinomycetes on starch casein agar, bacteriovorous protozoans by MPN on sodium chloride agar baited with Enterobacter, and fungal biomass carbon using buried slides were also determined. Soil respiration in different habitats was significantly influenced by type of cover, diurnal temperature variations and soil moisture. Soils under cover showed significantly higher soil respiration than the bare soils. Autochthonous bacterial populations in the Mopane woodland soils consisted mostly of oligotrophs which varied insignificantly between seasons. Fungi were the most dominant microorganisms in all the Mopane woodland soils, with biomass of 162.05 to 282.14 μg C/g soil in the wet season and 11.84 to 44.16 μg C/g soil in the dry season. Microscopic observation of buried slides revealed that fungi play a vital role in holding soil particles together in these soils. The results showed a strong positive relationship between changes in fungal biomass and fluctuation of soil respiration. However, no clear correlation was observed between the variation of soil respiration and other microbial populations (oligotrophic bacteria, actinomycetes, and nitrifying bacteria). Overall these results indicate that in soils under Mopane tree canopy, fungi contribute significantly to soil structure and soil respiration. Other microbial populations consist mostly of oligotrophs which show minimal seasonal variations. Soil moisture significantly influences seasonal fluctuation in soil respiration. URI: http://hdl.handle.net/10311/292 Files in this item: 1
The Effects of Soil Cover.pdf (6.625Mb) -
Omari, K.; Mubyana, T.; Matsheka, M.I.; Bonyongo, M.C.; Veenendaal, E. (South African Journal of Botany http://www.elsevier.com/wps/find/journaldescription.cws_home/707238/description#description, NaN, 2004)[more][less]
Abstract: Effects of flooding on soil nitrogen (N), and asymbiotic nitrogen fixing bacterial (diazotroph) populations of the Okavango Delta were investigated. Diazotrophs from the rhizosphere of dominant annual and perennial grasses of the Okavango Delta were isolated on N-free composite media and identified applying morphological and biochemical criteria and Restriction Fragment Length Polymorphism (RFLP). Azotobacter species were found associated mostly with the grasses Andropogon guyanus and Vetevaria nigritiana (103CFU g–1 rhizosphere soil). Annual grasses such as Eragrostis inamoena, Setaria sphacelata as well as perennials showed insignificant populations (<101CFU g–1 soil). On the contrary, Azospirillum spp. was found associated with most of the grasses. Highest population densities (above 104MPN g–1 soil) were observed in rhizospheres of E. inamoena, Cympogon excavatus, Sporobolus acinifolis, Eragrostis lapila and Eragrostis rigidor and lowest population densities (below 102MPN g–1 soil) in rhizospheres of Andropogon guyanus and Panicum repens. Flooding increased the Azotobacter populations, while Azospirillum spp. populations were significantly reduced. Nitrogen-fixing sulphur reducers were observed in the rhizosphere of annuals (A. guyanus and P. repens) and only in perennials growing in flooded soils. No Beijerinckia species were found associated with any of the grasses. The highest soil nitrogen levels were detected in flooded soils (<0.20% N) while no N was detected in the rhizosphere soil of grasses growing in very dry soils (<5% moisture content). The results indicate that in the Okavango Delta, total soil nitrogen varies with flooding regime. With flooding, the diazotroph population shifts towards Azotobacter and Nfixing sulphur reducers while Azospirillum spp. are widespread in non-flooded soils. RFLP analysis of the 1 450bp amplicon using the restriction endonuclease Alu1, showed three different banding profiles, suggesting the occurrence of three different species of Azospirillum. URI: http://hdl.handle.net/10311/294 Files in this item: 1
Flooding and its influence.pdf (2.253Mb) -
Bonyongo, M.C.; Mubyana, T. (South African Journal of Science, http://www.sajs.co.za/, NaN, 2004)[more][less]
Abstract: WETLANDS SUCH AS THE OKAVANGO Delta, located in semi-arid regions, are of great ecological, environmental and socio-economic importance. In most cases, however, few data exist on nutrient cycling in these areas. This paper presents preliminary results of an ongoing study, which investigates the influence of seasonal flooding on soil nutrient status in the different vegetation communities of the delta. Soil K, Na, and pH significantly increased with a decrease in soil moisture, with the values increasing from the primary floodplains to the islands communities. Available P, Ca and Mg decreased as the elevation gradient increased from the riverbed. Although nutrient status generally was highest in the floodplain vegetation areas adjacent to the riverbed, there was no significant difference in available P, Ca and Mg within the vegetation communities. Calcium levels in the different vegetation zones were more influenced by rainfall than floodplain vegetation community. Higher soil Ca was observed in the rainy season, while elevated Mg was recorded after the rains. Overall, these results indicate that flooding is an essential aspect of the Okavango Delta as it may be a primary source of some of the soil nutrients that support the high diversity of plants sustaining the delta’s ecosystem. URI: http://hdl.handle.net/10311/401 Files in this item: 1
Soil nutrient status.pdf (1.635Mb)
Now showing items 1-3 of 3