Thesis (MTech (Horticultural Sciences)--Cape Peninsula University of Technology, 2012 / This study evaluated the effects of different combinations of Hoagland’s solution and Azolla filiculoides on Beta vulgaris subsp. cycla ‘FORDHOOK GIANT’ grown in different hydroponic nutrient solutions. These solutions were comprised of a full Hoagland’s solution and a Hoagland’s solution minus nitrogen solution and amalgamations of these with Azolla respectively. The objectives were to assess the effects of different combinations of Hoagland’s solution and A. filiculoides on uptake of nitrogen and other nutrients, photosynthesis, chlorophyll content, growth and development in B. vulgaris grown in hydroponic cultures. The treatments were made up of 1) Hoagland’s minus N solution (as the control), 2) A. filiculoides plus Hoagland’s minus N solution, 3) A. filiculoides plus a full Hoagland’s solution and 4) full Hoagland’s solution. Each treatment was replicated 4 times. Nutrient uptake was measured at 4 and 8 weeks into the experiment. Photosynthesis was measured by analysing the photosynthetic rate, stomatal conductance, intercellular CO2 concentration and the evapotranspiration rate of B. vulgaris on a weekly basis. Chlorophyll content was determined by analysing the samples at 4 and 8 weeks. Growth and development was determined by measuring plant height, leaf number, leaf colour, fresh weight and dry weight. Plant height, leaf number and leaf colour on a biweekly intervals, while fresh and dry weight were analysed at 4 and 8 weeks into the experiment. In this study, the most favourable results were attained by the full Hoagland’s solution. This treatment produced plants with the highest nutrient uptake, photosynthesis, chlorophyll content and best growth and development. Preceding this was the Azolla plus full Hoagland’s solution, followed by the Azolla plus Hoagland’s minus nitrogen solution. The poorest results were noted in the control (Hoagland’s minus nitrogen solution) as all the tested parameters in this treatment were the lowest. In this study, Azolla plus Hoagland's minus N solution treatment produced significant growth in B. vulgaris. Although nitrogen was not applied in this treatment, there was improved nitrogen content in B. vulgaris organs. It is postulated that, probably, Azolla released the fixed nitrogen in its surrounding environment making it available to B. vulgaris hence improving N uptake and growth. This implies that there was a synergistic effect from Azolla–Anabaena symbiosis. More studies to understand the mechanisms involved in improving the plant growth are recommended.

An autecological study of the heterosporous fern Azolla filiculoides Lamarck and its endosymbiotic blue-green alga Anabaena azollae Strasburger, based on a combination of field and laboratory studies, is presented. The taxonomy, morphology and anatomy of the fern-alga association were studied as well as nutritional and physiological aspects of the symbiosis. These studies have defined the habitat and nutritional requirements of the fern and have provided new insights into its reproductive biology, nitrogen metabolism and the nature of the association between the fern and alga. In the catchment area of the Hendrik Verwoerd Dam the availability of suitably sheltered habitat limits the distribution of A. filiculoides while the availability of nutrients, in particular calcium, phosphorus and iron, limits the growth of the fern. The multilayered mats formed by A. filiculoides are essential for spore production, cause dramatic changes in the hydrochemistry of the underlying waters and confer a great competitive advantage on the plant. Methods for the isolation of the fern and algal components of the symbiosis have been developed but recombination of the individual organisms to reform the symbiosis was unsuccessful. The development of the fern is closely linked to that of the alga and the association is maintained throughout the life cycle of the fern. Because of its specific habitat and nutritional requirements, A. filiculoides is unlikely to colonize the open waters of the Hendrik Verwoerd Dam.

In Mozambique, establishment of aquatic weeds has been enhanced through the increased enrichment of water bodies by nutrient runoffs from human and agricultural wastes that lead to an increase in nitrate and phosphate in the water. The aquatic weeds, water hyacinth (Eichhornia crassipes), red water fern ( Azolla microphylla), water lettuce (Pistia stratiotes) and salvinia (Salvinia molesta) were found in most watercourses in Mozambique and are becoming aggressive in some watercourses, especially in the Umbeluzi and Incomati rivers. Farmers and people living along the rivers are aware of the negative impact of the water weeds because the large mats of weeds cause loss of shoreline and navigability along the rivers. Other commonly perceived effects of aquatic invasive plants in Mozambique rivers include: reduced navigable surface area; difficulties for fishermen, which reduces income; increased prevalence of insects and insect-borne disease, and decreased aesthetic value. The methods currently used for the control and management of the aquatic weeds are mechanical and manual control. Both methods are costly, time consuming, and only provide a short-term solution to the problem. The study found that the weevils Neochetina eichhorniae and N. bruchi were effective biological control agents in the study area but their impact is too gradual compared to the aggressive proliferation of water hyacinth. The one year lab-experiment clearly demonstrated that the water lettuce weed had a significant impact on the recruitment of macro-invertebrates to the artificial substrates, and water lettuce contributed to the reduction of oxygen in the water and consequent reduction of macro-invertebrate abundance and diversity. The biodiversity recovered at the same time in the pools containing water lettuce controlled by N. affinis and water lettuce controlled by herbicide, but richness and diversity of macro-invertebrates was higher in the water lettuce controlled by N affinis during the first sampling occasion compared to the water lettuce in pools controlled by herbicide, where macro-invertebrates increased only when DO levels recovered after water lettuce mat decay. The number of taxa recorded in this study is an indication of the significance of macro-invertebrates in an aquatic environment. This therefore emphasizes the need for more research efforts into macrophyte and macro-invertebrate associations in the aquatic system to better understand the implications of habitat modification arising from human activities. It will also enable us to be better equipped with a more appropriate ecological understanding for aquatic resources management.