Themeda triandra is a grass species of economic importance in Southern and Eastern Africa, and Australia. The species is being lost from grasslands and savannas in these areas due to poor agricultural practice, rangeland degradation, opencast mining and increased afforestation. Based on the poor re-establishment of the species from seed in sub-climax grasslands, dogma holds that T. triandra can not be re-established from seed. Recent research has, however, highlighted the potential to establish this species from seed, but the use of seed of T. triandra in re-vegetation of disturbed areas is limited by poor understanding of the seed biology of the species and low seed availability. In this Thesis ways to maximise the use of available seed are reported. Areas investigated include optimisation of seed storage conditions, overcoming primary seed dormancy, promoting germination of available seed and pre-treatment of seed to improve germination. The Thesis closes with an investigation of the environmental limits of tolerance of seedlings from the T. triandra ecotypes studied, when grown under field conditions at reciprocal sites. Two altitudinally and geographically distinct populations of T. triandra were studied; a high altitude grassland population at Cathedral Peak (Drakensberg: 1800 m) and a low altitude savanna population from the Umfolozi Game Reserve (Zululand: 90 m). At seed shed T. triandra seed is dormant. The depth and duration of primary seed dormancy varies between populations, but appears to reflect severity of the winter period experienced. More than 95% of T. triandra seed from the Drakensberg population was dormant at seed shed, compared to 55% of seed from the Zululand population. In both populations dormancy is lost during dry after-ripening. At seed shed T. triandra seed displays a high level of seed viability (> 80%). Seed temperature range -15°C to 70°C, was achieved at 25°C (± 2°C), at which temperature seed was held for 40 months. During this period viability decreased from over 80% to 50% and dormancy was lost through dry after-ripening within four (Zululand) to eight (Drakensberg) months. Loss of dormancy can be accelerated at higher temperatures, but is accompanied by rapid loss of seed viability. In contrast, viability can be maintained in storage at sub zero temperatures, but loss of dormancy is retarded. Loss of dormancy coinsides with the onset of spring. Dormant seed is capable 'of germination at a narrow range of constant temperatures (25 ° C to 40 ° C). With after-ripening, the range of temperatures at which germination takes place increases (15 ° C to 40 ° C) and the optimum temperature for germination decreases from 30 ° C in both populations to 25 ° C. After-ripened seed is capable of germination at lower water potentials than dormant seed. Similarly, seed from the low altitude population is capable of germination at lower water potentials (-1.0 MPa dormant: -1.5 MPa after-ripened) than seed from the high altitude population (-0.5 MPa dormant: -1.0 MPa afterripened). Dormancy in seed from the high altitude population is overcome by prolonged stratification (30d). In contrast, seed from the low altitude population responds to short duration stratification (5d) with longer periods proving detrimental to seed germination. Germination of dormant and non-dormant seed of T. triandra does not differ significantly in the light or dark. Neither does photoperiod, or red / far-red light exposure significantly affect germination. Seed response to light and temperature, as characterised under controlled conditions, was verified in a field seed burial experiment undertaken at the high altitude Drakensberg site during winter. Burial in soil does not affect the response of T. triandra seed to light or temperature. Loss of dormancy is accelerated in buried seed. After-ripened seed germinates over a wider range of temperatures than dormant seed. The mechanisms governing T. triandra seed dormancy and germination appear to be universal between ecotypes. Dormancy is enforced, in part, by the seed covering structures (glumes) which impose a mechanical restraint to radicle emergence. Approximately 85% of dormant seed, however, contains a dormant embryo. Embryo dormancy is enforced at seed shed by compounds inhibitory to seed germination. The germination process in T. triandra appears to be governed by endogenous gibberellins. Bioassay results reveal that endogenous gibberellin synthesis commences up to six hours sooner in after-ripened seed than in dormant seed and that the level, or concentration, of gibberellin-like compounds is substantially lower in after-ripened seed than in dormant seed. Similarly, the concentration of applied gibberellic acid required to achieve maximum germination of T. triandra seed decreased from 500 mg.l ¯¹ (8 week old seed) to 50 mg.l ¯¹ (78 week old seed) as dormancy is lost during after-ripening. Contrary to previous reports, boron does not promote T. triandra seed germination. Plant-derived smoke significantly promotes T. triandra seed germination (5% to 43% for dormant seed from the Drakensberg population). The effectiveness of smoke in promoting germination increased with increasing seed imbibition suggesting smoke action at a metabolic level. This suggestion is reinforced by the ability of smoke to bring about the germination of seed which had failed to germinate in water. Moreover when smoke is applied in combination with gibberellic acid the final level of seed germination following combined treatment is significantly greater than the level of germination achieved in the presence of either smoke or gibberellic acid alone. A similar result is achieved with joint application of smoke and kinetin, although the results were not statistically significant. Furthermore, smoke treatment reversed ABA-induced inhibition of germination of non-dormant T. triandra, wheat, radish and sunflower seed to a level equal to or greater than that achieved using GA[3] or kinetin. The possibility that smoke promotes seed germination by mimicking, or promoting the synthesis of endogenous gibberellins was investigated. Bioassay results revealed that smoke had no effect on increasing the level of endogenous gibberellin-like activity in T. triandra caryopses. The mechanism by which smoke acts to promote seed germination remains elusive, however results presented suggest that smoke may act to remove an ABA-induced block to seed germination. Consequently, it is suggested that smoke plays a permissive role in promotion of T. triandra seed germination by removing a block to the seed germination process thereby allowing endogenous gibberellins to act. Treatments which significantly improved the level of T. triandra seed germination were evaluated as seed pre-treatments. Significant improvement in germination was obtained following smoke (aq) and gibberellic acid (100 mg.l ¯¹) pre-treatment of seed. The effects of pre-treatment were evident on germination of seed for up to 21 days after pre-treatment. Seed pre-treatment with smoke had no affect on subsequent seedling growth, but gibberellic acid pre-treated seedlings developed abnormally. In contrast, short duration exposure of dormant seed to high temperature (70 0 C for 7 days) increased germination, seedling height and tiller number. Priming of seed in polyethylene glycol (PEG 8000) for 7 days significantly improves the level of T. triandra seed germination. The use of seed pre-treatment to maximise germination of T. triandra seed is discussed. Reciprocal transplanting of seedlings from both the Drakensberg and Zululand populations confirmed that the T. triandra populations under investigation are distinct ecotypes. Field transplant gardens were established in the Drakensberg, Zululand and at an intermediate altitude in Pietermaritzburg (800m). Less than 10% of planted seedlings died at any site. With increasing altitude of the field site, tiller number increased, but tiller allocation to reproduction decreased. Similarly, for both Zulu land and Drakensberg seedling transplants the time taken to reach anthesis increased with increasing altitude and the proportion of transplants which flowered decreased. These data are consistent with the climate of the field sites where the high altitude site experiences a short growing season and harsh winter while the Zululand site experiences a prolonged growing season and mild winter period. These data indicate that T. triandra ecotypes are tolerant of a wide range of environmental variables. The application of the data presented in this Thesis, in maximising the use of available seed of T. triandra for use in re-vegetation, is discussed. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1996.

Soil erosion and vegetation destruction have reached serious proportions in disturbed areas of the montane grasslands of the Natal Drakensberg. Little is known of the inherent ability of indigenous grasses to produce viable seed and establish seedlings for rehabilitation programmes. This study examined the effects of fire and small-scale disturbance on the seedling dynamics of the dominant grass, Themeda triandra Forssk. Annual seed production of T. triandra increased with length of burning rotation, ranging from 21 seeds m⁻² in the annual winter burn to 485 seeds m⁻² in the five-year burn. High predation of seeds (70-98%) and low viability (37% in 15 month-old seeds) contributed to the poor representation of T. triandra in the seed bank when compared to the aboveground vegetation. Seedling densities and survival were monitored by mapping quadrats at six-weekly intervals from November 1986 to September 1989. Highest establishment of T. triandra was recorded in the biennial spring burn treatment (< 184 seedlings m⁻²). Microclimatic studies of the seedling environment demonstrated that increases in photosynthetically active radiation following burning, and high soil moisture associated with accumulation of litter, favour seedling establishment. The main constraint to seedling establishment was high mortality in winter which resulted in a 1% survival of seedlings of T. triandra during the three-year study. This indicates that in the fire-climax grasslands of the study, seedlings contribute little to the population structure. The most significant factor contributing to low survivorship is intraspecific competition between seedlings. Spacing of seedlings in rehabilitation programmes is therefore a critical factor in optimizing seedling establishment. Analysis of the fate of seeds of T. triandra between their production and establishment, showed that the main constraints for seedling establishment were predation, low viability and poor germination. A population model, based on transitions between seeds, seedlings and mature tufts, predicts that a biennial spring burn is the optimal treatment for maximising both seedling establishment and vegetative growth. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

Mycorrhizal fungi are soil-borne organisms that form symbiotic associations with the majority of land plants. These fungi gather and exchange mineral nutrients with plants for photosynthetically derived carbohydrates. Mycorrhizal fungi can also confer other benefits onto plants, e.g. defense against pathogens, improved water relations, tolerance to heavy metal toxicity and herbivory. The influence of mycorrhizal fungi on plant mineral nutrition and response to stress suggests that these organisms may have a role to play sustainable agriculture as well as in bioremediation and ecosystem restoration. In contributing to this important research, I investigated host-specific interactions between mycorrhizal fungi and the sex morphs of the gynodioecious perennial herb Polemonium foliosissimum (Polemoniaceae) and their mycorrhizal associates in the field. I hypothesized that the genders of this species differed in their associations with mycorrhizal fungi in benefits received. I performed a full factorial simulated herbivory experiment and evaluated the extent of mycorrhizal colonization in the roots as well as the concentrations of nutrients in leaf tissue. Mycorrhizal colonization and leaf nutrient concentrations did not differ between the genders nor were influenced by the experimental treatments. This suggests that the genders of Polemonium foliosissimum do not interact differently with mycorrhizal fungi, and thus do not represent different "hosts". Also, I investigated local adaptation of mycorrhizal associations by exploring the effect of large herbivore grazing on plant-mycorrhizal associations. I hypothesized that grazing by large herbivores results in locally adapted symbioses that enhance plant response to herbivory. I grew the perennial bunchgrass Themeda triandra (Poaceae) in inoculum prepared from soils collected from three field exclosures with differing histories of large herbivore exclusion in the Kenya Long Term Exclosure Experiment. I conducted a full factorial simulated herbivory experiment in which plants were subject to two clipping events over the course of 5-months, and evaluated plant regrowth as well as mycorrhizal colonization for plants in the experiment. Plants grown in inoculum from exclosures in which large herbivores have had access produced more root mass when mycorrhizal fungi were present. Further, I found equivalent biomass production of clipped and non-clipped plants in inoculum prepared from the exclosure with only native large herbivore access while equivalent biomass production was not found in the substrate prepared from areas with a history of large herbivore exclusion. This suggests that mycorrhizal fungi mediate plant growth and response to herbivory in this system.

The main project was an assessment of the effect that colonization by five different Vesicular-arbuscular mycorrhiza (VAM) cultures have on the growth of the indigenous-grasses Themeda triandra and Trachypogon spicatus, when grown on coalmine topsoil. With unamended topsoil, VAM showed the ability to significantly increase the growth of the grasses compared to non-VAM control plants. The amount of effect varied with the VAM inoculum culture type, with a VAM culture originally from the Cape Flats being the most effective. In a second trial, soil fertilized with nitrogen, potassium and low concentrations of phosphate (P) was used. Again VAM displayed the ability to improve grass plant growth. The increase in P caused the Large spore inoculum to become the most effective. This indicated that different VAM cultures are inhibited to different degrees by an increase in phosphate fertilization. The low level of VAM infection, in both trials, seemed to preclude most of the VAM associated nutrient uptake control. Varying reports have been published on the effect of fertilization on VAM infection and colonization. In an attempt to further elucidate the role of fertilizer in VAM inhibition, rhizosphere soil from a long term fertility trial near Witbank, S.A. was sampled. Amcoal environmental services fertilized forty-two plots with varying concentrations of nitrogen, potassium, phosphate and lime to assess the growth of a variety of grasses. The trial had been maintained for ten years before sampling was completed for this project. Samples from each plot were taken from the rhizosphere soil of the most prominent grass (Digitaria eriantha). VAM spores were extracted from all the samples and five different types of spores were identified and counted for each sample. By comparing spore counts from each plot, the effect that the fertilizer regime had on the VAM on that plot could be assessed. Variation in the concentrations of nitrogen (N) and potassium had no significant effect on VAM colonization. Very low concentrations of N could not be assessed as all plots had been initially top dressed with nitrogen fertilizer. Phosphate (P) fertilizer concentration had a marked effect on spore concentrations. There was a significant increase in spore concentration as P levels were increased from zero P fertilization to 80kgs P/ha. Further increase in P to ≥ 60kgs P/ha resulted in a significant decrease in spore concentrations. From this it would appear that a low level of soil P is needed to give maximum VAM colonization and further increase in soil P causes VAM inhibition. Lime ameliorated the VAM inhibition caused by high concentrations of P. Increase in P caused spore concentrations of low abundance propagules (LAP) too decreased more rapidly than high abundance propagules (HAP). In high P soils VAM with LAP would eventually be eliminated from the system resulting in a decrease in VAM diversity. A project was attempted to use the recently developed Randomly Amplified Polymorphic DNA in conjunction with the Polymerase Chain Reaction (RAPD PCR) techniques to identify different VAM families. The technique causes the amplification of segments of DNA which can be visualized by gel electrophoresis and staining. Band patterns formed can be related to the VAM of origin and hence used in identification of that VAM. An attempt was made to amplify DNA from a single spore in this manner which would, in conjunction with morphological observations, make identification of VAM easier and more accurate. Problems with either releasing the DNA from the spores, or substances in the spore inhibiting the PCR reaction made obtaining band patterns difficult. After many PCR attempts, varying extraction methods and PCR conditions, no repeatable results could be obtained and work on this project was discontinued. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.

No abstract available. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.

A series of pot trials were undertaken to test the growth of indigenous grasses (Themeda triandra and Cynodon dactylon) on mine capping soil, treated with various soil ameliorants. The capping soils were obtained from open cast coal mines (Optimum Mine and Syferfontein Mine) in the Mpumalanga Highveld, south of Witbank. However, because mine soil was not available at the commencement of the project, the initial pot trial used soil from the Umlazi Landfill in Durban. The trials were the Umlazi Landfill Trial, Microbe Trial, Legume Trial and Fly Ash Trial. For the Umlazi Landfill Trial, landfill top and subsoil was used along with fertilizer, sewage sludge, K-humate, lime and microbes. The soil ameliorant treatments for the Microbe trial were Trichoderma harzianum (Eco'T), Bacillus subtilis Strain 69 (B69) and Bacillus subtilis Strain 77 (B77), for the Legume Trial, Medicago sativa, phosphorus and/or potassium were applied. For the Fly Ash Trial, lime and fly ash were introduced. From the Landfill trial it was shown that fertilizer and sewage sludge significantly increased the above ground, below ground and total biomass of T. triandra, further, there were no significant treatment differences between fertilizer and sludge. The lime treatment for this trial, surprisingly, significantly reduced below ground biomass but the application of microbes (B69 and BcoT) alleviated this negative effect. However, in the Microbe Trial the microbes (BcoT, B69 and B77) had a negative or no effect on the biomass of T. triandra and C. dactylon. In the Legume Trial it was shown that the above ground biomass of T. triandra was significantly reduced when grown with M. sativa. The Fly Ash Trial revealed that the lime and fly ash treatments had no effect on the biomass of M. sativa and T. triandra, and they did not maintain a reduction in soil acidity. The results therefore indicated that either organic fertilizer or sewage sludge could be used to significantly improve the growth of T. triandra. It was also suggested that lime not be applied to soils with an acid saturation of approximately 1%, as this could retard plant growth. The application of microbes and the growth of a legume with grass, although both have been recorded to have beneficial effects in aiding plant growth, in the short-term however, the application of T. harzianum, B. subtilis Strain 69 and 77 applied to the soil while growing T.triandra and C. dactylon and the growth of M. sativa with T. triandra is not recommended. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.