Thesis--Catholic University of America. / Bibliography: p. 58-60.

No description available.

Thesis(M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

Grass species within South Africa show a photosynthetic subtype and phylogenetic response to rainfall gradients, with Panicoideae species (NADP-Me and NAD-Me) inhabiting mesic environments, while Aristidoideae species (NADP-Me) inhabit more arid environments. It is predicted that climate change will alter rainfall patterns within southern Africa, which could have implications for grassland distributions and functional composition. Globally, and in South Africa, species distributions indicates that NAD-Me species have a preference for more arid environments, but this may be complicated by phylogeny as most NAD-Me species belong to the Chloridoideae subfamily. Additionally, differences in the metabolism and energetic requirements of different carboxylation types are expected to confer different ecological advantages, such as drought tolerance, but the role of these different pathways is not well understood. Based on natural distribution and photosynthetic subtype differences, it was hypothesised that Panicoideae NADP-Me species would be less drought tolerant than Panicoideae NAD-Me and Aristidoideae NADP-Me species and that subtypes and lineages would show different drought recovery rates. Furthermore, drought sensitivity would be of a metabolic and not a stomatal origin and plants that maintained favourable leaf water status would be more drought tolerant and recover faster. This was tested experimentally by comparing Panicoideae species (NADP-Me and NAD-Me) and NADP-Me species (Panicoideae and Aristidoideae). Plants were subjected to a progressive 58 day drought period and a recovery phase where gas exchange, chlorophyll fluorescence and leaf water relations were measured at select intervals. In conjunction with this, a rapid drought experiment was performed on Zea mays (NADP-Me: Panicoideae) plants where similar parameters were measured. Photosynthetic drought and recovery responses showed both a subtype and phylogenetic response. Panicoideae species were less drought tolerant than Aristidoideae species, although Panicoideae NAD-Me showed better recovery rates than Panicoideae NADP-Me species, while Aristidoideae species recovered the quickest. Panicoideae NAD-Me and Aristidoideae species maintained higher leaf water status during drought which contributed to the maintenance of PSII integrity and thus facilitated rapid photosynthetic recovery. During drought Panicoideae species showed greater metabolic limitations over Aristidoideae species and for the first time, lower metabolic limitations were associated with osmotic adjustment. This is a novel finding whereby osmotic adjustment and the subsequent maintenance of leaf water are key to preventing metabolic limitations of photosynthesis in C₄ grasses. Results from the Z. mays rapid drought study showed the limitations to photosynthesis were exclusively metabolic and unlikely to be a direct consequence of turgor loss. It was apparent that the response to drought was stronger amongst lineages, as NADP-Me species from different subfamilies showed a significant difference in drought tolerances. Aristidoideae species’ exceptional drought tolerance and predicted increased aridification could favour these species over Panicoideae species under future climates.

Purple threeawn (Aristida purpurea Nutt.) is a native bunch grass that is avoided by grazers. It is capable of dominating old cropland and overgrazed pastures, limiting livestock carrying capacity, and degrading wildlife habitat. Traditional management tools have had little impact on threeawn dominance in semiarid regions of the west. Our objectives were to: 1) assess fire and nitrogen treatment effects on threeawn forage quality at various phenological stages to test their potential as pretreatments in a grazing strategy and 2) examine a threeawn-dominated plant community’s response to prescribed fire, nitrogen addition, and clipping. Fire improved threeawn forage quality with greater improvements in early phenological stages. Nitrogen had little effect on forage quality. Fire and nitrogen reduced threeawn while increasing cool season grasses. Light and moderate clipping following fire did not improve the efficacy of fire. Fire appears to an effective preliminary treatment to improve the chance of herbivory.

Aristida junciformis subsp. junciformis Trin. et Rupr. is an indigenous, densely tufted, evergreen perennial grass associated with the degeneration of grasslands over large areas of South Africa. More than two hundred thousand square kilometres of veld, c. 17% of the total land area of South Africa, contains A. junciformis. The aim of this study was to improve our understanding of the mechanisms by which this species invades and dominates grassland, specifically in this study, Southern Tall Grassveld. Aristida junciformis also has a low nutritional value resulting in a very low grazing value. The unpalatability of the plant is due to the high tensile strength of the leaves, whose hard, fibrous laminas are very difficult for a grazing animal to crop once their length attains 30 cm or more. This species lack of response to conventional grazing practices has often resulted in a grassland in which the carrying capacity has diminished to such an extent as to be virtually useless for grazing in a relatively short time. The extent of encroachment of veld by A. junciformis appears dependant on the frequency of disturbance and rest afforded to the veld. Annual burning and mowing maintained the species composition of A. junciformis at levels <10% whilst protection from fire, burning or grazing allows this species to dominate the herbaceous layer at levels approaching 90%. Aristida junciformis does not become moribund and is unlikely to die if left undefoliated. As the abundance of A. junciformis increases, veld deterioration gradually accelerates through increased selective grazing on remaining palatable species. Competition from adult A. junciformis plants increases the mortality of seedlings and constrains growth of surviving seedlings. Tiller production of Aristida junciformis seedlings declined from an average of 5.2 tillers per seedling in a no competition situation to 2.2 tillers per seedling when subjected to full competition. Tiller production of T. triandra seedlings decreased from 9.6 tillers per seedling free from competition to 3.3 tillers per seedling subject to full competition for resources. Once these seedlings have become adult plants they are avoided by grazing animals and grazing pressure on the remaining palatable species consequently increases. This allows the A. junciformis plants to increase their size and density in the sward. Once this density is sufficiently high, grass seedlings of either A. junciformis or more desirable grass species such as T. triandra are unable to establish, eventually resulting in a monospecific stand of A. junciformis if left undisturbed. Large amounts of caryopses are produced by A. junciformis - up to a 19 000 caryopses from a large mature plant (c. 38 000 caryopses/m²). Of these c. 40% is likely to be infertile but the remaining c. 60% viable caryopses are dispersed in a typically leptokurtic distribution, the number of caryopses dispersed rapidly declining within a 10 metre radius. A large proportion of the caryopses was trapped in surrounding foliage but in open swards caryopses had greater opportunity to be blown further distances than in a closed sward. The density of A. junciformis caryopses on the soil surface was positively correlated with the density of flowering adult plants in the area and varied from 400 caryopses/m² (density of parent plants c. 0.6 plants/m²) in less effected areas to 11000 caryopses/m² (density of adult plants c. 6 plants/m²) in severely encroached areas. The primary function of the three awns appears to be orientating the caryopsis correctly for in its descent from the parent plant to expedite germination. Caryopses orientated vertically with the awns uppermost exhibited the highest and most rapid germination (67%) compared to caryopses lying horizontally (35%) whilst only 1% of inverted caryopses germinated. Caryopses trapped in litter and effectively held off the soil surface failed to germinate. Removal of the glumes from A junciformis seed greatly enhanced the rate and overall germination of the seed except for inverted seed of which <1% germinated. The highest numbers of A. junciformis seedlings (32 seedlings/m²) were found in those areas with the highest density of caryopses on the soil surface. Despite the large amounts of caryopses produced, dispersed and landing in apparently suitable micro-sites for germination, comparatively few A. junciformis seedlings (n=992) were found and overall germination ranged between 1 % and 4% of the initial caryopses density on the soil surface. Seedling survival through winter was low with only 13% surviving to the following spring. The basal areas of A. junciformis increased overall by 66% whilst that of other grass species increased overall by only 3% in the time monitored. These results suggest that the primary method of encroachment of A. junciformis in the grass sward appears to be through vegetative expansion and not seedling recruitment. Frequent defoliation of the sward and avoidance of overgrazing to enhance the competitive abilities of palatable species and provide as high a fuel load as possible appear to be the most economically and logistically feasible ways to remove or at least inhibit A. junciformis veld encroachment at present. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.

MENVSC / Department of Ecology and Resource Management / Certain communities in Sekhukhune area are known to be practicing geophagia. Existing standard questionnaires as adopted to generate data on human geophagia included aspects on demography, socio-economics, cultural, ecological, physico-chemical aspects, indigenous knowledge and health effects of geophagic consumers. These data were gathered through distribution of questionnaires to 200 geophagic participants, of which 135 were from Ga-Nchabeleng Village and 65 from Mphanama Village. Both the Villages were based in the rural settlements in Sekhukhune area. In this study the behaviour of geophagic individuals was investigated and cytotoxicity of plant remains consumed in geophagic soils was evaluated for any toxicity. A total of 17 different geophagic sites were identified. Six geophagic sites each were from Ga-Nchabeleng Village and six from Mphanama Village. Five other sites were selected from sites where geophagia was not practiced and were recorded as the control sites. All the 17 soil samples were analysed using Munsell Soil Color charts for soil colour classification. Samples of plant remains were collected from the same geophagic sites where soil samples were collected. Due to similar plants and vegetation type from 17 different geophagic sites, a composite study was adopted. Geophagic consumers in Ga-Nchabeleng Village identified four plant species of plant remains consumed in the soil in the area and Mphanama village identified five species different from Ga-Nchabeleng plants. Samples of plant remains were grouped according to comparable features or characteristics. Sample 1 of plant remains was composed mainly of grasses; Cynodon dactylon, Aristida congesta and Eragrostis rigidior whereas sample 2 of plant remains was composed of Acacia plant; Vachellia tortilis. The two samples of plant remains were collected from Ga-Nchabeleng Village. Sample 3 of plant remains was composed of creeping, perennial weed herbs; Alternanthera pungens Kunth and Alternanthera lorentzii. Sample 4 of plant remains was composed of prominent woody plants; Combretum apiculutum, Kirkia wilmsii and Boscia albitrunca. Samples of plant remains 3 and 4 were collected from Mphanama Village study sites. Sample 5 of plant remains was the control site and composed mainly of Acacia plants; Vachellia nilotica, Acacia vii mearnsii and Vachellia tortilis and were collected from sites not used for geophagic practices. The plant remains parts mostly consumed were roots (50%) in Ga-Nchabeleng, whereas in Mphanama Village they were stems (54.5%) and the control site had leaves at 62.5%. The five samples of plant remains were recovered using physical separation method. The plant remains were washed and dried. Retch Muhle grinding machine was used to ground the samples. Methanol was used in the extraction of all the samples of plant remains. The result from the administration of the questionnaire revealed that geophagia in this area was practiced by both male and female Sepedi-speaking individuals. Ga-Nchabeleng Village had more female geophagic participants, whereas Mphanama Village had more males who have almost undergone secondary school. However, in general for the study there were more female geophagic consumers. Geophagic consumers ingest soil known locally as Mobu, Letsopa or Leraga collected mostly from the riverbanks, mountains/hills and valleys with only a few that indicated termite mounds. Geophagic consumers in the study used colour, among other things, to describe their soil of preference. The study consisted of 200 participants of whom 172 represented the geophagic group and 28 were the control group, aged between 18-65 years analysed using chi-square crosstabulation. There was no significant difference in human health effects associated with geophagia between the geophagic group and the control group. There was also no association established between soil consumption and other non-food substances between geophagic group and control group. Chi-square (χ2) analyses revealed a significant association of gender with geophagic habits (p<0.05), while there was no association of age, educational level, income source and marital status (p>0.05) with geophagic habits. Findings of the survey when two villages are combined revealed that more females (75.60%) practice geophagia compared to males (24.40%). The respondents from both study sites preferred digging technique when collecting the soil. It was established that craving was mainly the reason behind the practice in the study area. Hygiene and environmental conditions were not considered when mining viii geophagic soil as the majority of them used dirty utensils, hands for collection and non-sterile bags and tins for packaging. Some of the soils were collected close to waste dumping sites as seen whilst visiting geophagic mining sites. Majority of the consumers had little or no knowledge that the soil could be harmful or if it contained any contaminants. This sample of interviewees provided valuable information on human geophagic practices in Sekhukhune area. It became clear that this practice was entrenched in the cultural behaviour of people in the area and a need for educating them on health related aspects. The cytotoxicity of methanolic extracts of plant remains on HEK-293T cell line was evaluated using MTT (3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) assay for cell viability. The 50% cytotoxic concentration (CC50) was defined as the compound’s concentration (500, 250, 125, 62.5, 31.25, 15.625 and 7.8125 μg/ml) required for the reduction of cell viability by 50%. Evaluation of cell viability showed the methanolic extracts of plant remains on HEK-293T cell line ranged in the order of plant remains extract=3>1>4>2>5 according to their cytotoxicity activities. Plant remains extract 3 from Mphanama Village showed high cytotoxicity with a CC50 of 13.75 μg/ml, followed by plant remains extract 1 at 16.68 μg/ml, plant remains extract 4 at 58.95 μg/ml, plant remains extract 2 at 92.75 μg/ml and the control at 251.4 μg/ml, respectively. In the study only the methanolic extract was investigated for cytotoxicity using HEK-293T cell line. Further research need to be conducted on the individual plants of each plant remains to be able to have conclusive results on the cytotoxicity profile. This will indicate which specific plant part is toxic or whether they exhibit a higher CC50 only when in combination.