In this study the contribution of the climatic factors such as temperature, altitude, and mean annual precipitation as well as phylogeny to the determination of the distribution of C₃ and C₄ genera of Cyperaceae in South Africa has been investigated. Multiple regression analysis was used to determine the climatic factor that best predicted percent C₄ distribution. To see if the C₄ syndrome was influenced by taxonomy, the percentages of C₄ species was determined for each of the subtribes and genera. The results show that the relationship between the climatic factors and percentage of C₄ Cyperaceae species is similar to what has been found for the grasses (Vogel et al., 1978). However C₃ species of Cyperaceae seem to be abundant in most parts of South Africa. Only minimum growing season temperature showed significant correlation (P = 0.000391) with percentage C₄. The presence of the C₄ syndrome is shown to have some consistency within subfamilies, tribes and genera.

Thesis (M .S.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science degree in Biology." "A thesis entitled"--at head of title. Bibliography: leaves 14-24, 51-60, 92-96, 121-123.

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Plants that come early in succession predominantly prefer_ ammonium form of nitrogen than nitrate. The hypothesis that Cynodon dactylon (L.) Pers., a grass in the primary succession stage would respond well when supplied with ammonium than nitrate fertiliser was tested. Seedlings of Cynodon dactylon were grown in culture solution and fertilised with either ammonium sulphate or potassium nitrate at ~ continuous concentrations of 200 ppm, 400 ppm and 600 ppm in the growth chamber. In support of my hypothesis, growth of Cynodon dactylon was greater from ammonium than nitrate nutrition in terms of aboveground and total plants yields at 200 ppm and 400 ppm and this was associated with efficient utilisation of this form of nitrogen by this species. Production from the nitrate treatments was restricted and showed no change with increase in external nitrogen supply. Decreased dry weights from the ammonium nutrition at 600 ppm were associated with toxicity of ammonium ions in plant tissues. High levels of nitrogen measured from the nitrate treatments were associated with the soluble nitrogen that was not assimilated for yield increase by this grass, Uptake of ammonium ion was shown to result· in high of uptake phosphorus. This study shows that Cynodon dactylon has the capacity for increased growth under ammonium nutrition while this was limited in the nitrate nutrition. However, response is restricted when excessively fertilised with ammonium nitrogen.

This study was carried out on Sand Plain Lowland fynbos at Pella from April to September 1988. Environmental factors, nitrogen and phosphorus pool sizes and mineralization processes were investigated in the surface soils (1-10cm) of 7-8 year old fynbos vegetation and an adjacent Acacia saligna (Labill.) Wendl. infestation. While there was no significant difference in soil temperature between fynbos and acacia sites, soil moisture and organic matter content was significantly higher in the acacia soils. This favoured decomposition so that soil nutrient analyses showed enrichment of the soils (higher N and P) by the acacia infestation. Soil N and P mineralization was assayed using in situ incubations. Due to their higher soil total N concentrations, acacia soils showed greater inorganic N concentrations. In both acacia and fynbos soils ammonium was the dominant N form. This was ascribed to the high soil moisture content, while the low temperatures appeared to be the factor most strongly influencing ammonium accumulation. The low nitrate accumulations even in the field incubations indicated that the nitrification process was inhibited, probably by the high soil moisture content and low temperatures. The variable patterns of inorganic P accumulation were ascribed mainly to fluctuations between microbial mineralization and immobilization. Contrary to the hypothesis that the higher soil organic matter and greater concentrations of total N and Pin acacia soils would result in higher mineralization rates, there was no significant difference in the rates of N and P mineralization between fynbos and acacia soils. Thus, it was concluded that the higher decomposition rates in acacia soils was not associated with greater mineralization rates during the wet season (period of study).

Protea lepidocarpodendron grown on low, medium and high nutrient treatments exhibited the lowest, and similar evapotanspiration rates respectively over a 9 day water stress cycle (experimental period). In stressed and unstressed treatments, stomatal conductance and transpiration rates of plants grown on the low nutrient treatment was generally lower than that of plants grown on the medium and high nutrient treatments where stomatal conductance and transpiration rates were similar. Stressed plants grown on the low, medium and high nutrient treatments exhibited the lowest, intermediate and highest photosynthetic rates respectively. Stessed plants grown on the medium and high nutrient treatments exhibited a dramatic decrease in transpiration rates ands stomatal conductance from day 5 to 7, and a dramatic decrease in photosynthetic rates from day 3 to 7. Stressed plants grown on the low nutrient treatment showed a far less dramatic decrease in transpiration rate, stomatal conductance and photosynthetic rate over the 9 day period. For stressed plants, photosynthetic rates varied between 0.08-5.39 uMOLm⁻²s⁻¹, 1.17-7.48uMOlm⁻²s⁻¹ and 1.15-8.65uMOLm⁻²s⁻¹ for plants grown on low, medium and high nutient treatments respectively. Unstressed plants grown on low. medium and high nutrient treatments exhibited the lowest, highest and intermediate photosynthetic rates respectively. In all stressed treatments, photosynthetic rates showed a steady decline from day 1 to day 7, whereafter a dramatic increase occurred in the medium and high nutrient treatments, and a less dramatic increase in plants grown on the low nutrient treatment. These decreases and increases in photosynthetic rates was not parallelled in the stomatal conductance and transpiration rates of the unstressed plants. For unstressed plants, photosynthetic rates varied between 1.4s-4.4 uMOLm⁻²-s⁻¹, 1.65-6.7 uMOLm⁻²s⁻¹ and 3.42-8.76 uMoLm⁻²s⁻¹ for plants grown on low, medium and high nutrient treatments respectively. Plants grown on low nutrient treatments exhibited the highest LSW (182.3 gm⁻²), highest whole plant mass (WPM) (1.07g), followed by high (LSW=1.76 gm⁻²,WPM=0.83g) and medium (LSW=167.28 gm⁻² ,WPM=0.79g) nutrient treatments. Total plant nitrogen content was inversely related to LSW and WPM on low (3.84 mgNplant⁻¹), high (4.18 mgNplant⁻¹) and medium (5.28 mgNplant⁻¹) treatments. Root : ratio between treatments were similar.

As there is still a major debate on how trees and grasses manage to coexist in the savanna biome, the niche separation by phenology hypothesis (Scholes and Archer 1997) was tested by observing the seasonal variation in carbon and nitrogen concentrations in leaves and young twigs of two deciduous species, Combretum apiculatum and Terminalia sericea. The study was carried out in the sub-tropical savanna biome in southern Kruger National Park, South Africa. Photosynthetic readings show a decrease in leaf activity towards the end of the growing season. There was no significant change in the carbon concentrations over the months for both species sampled but there was a significant decrease in leaf nitrogen for C. apiculatum. T. sericea experienced relatively no nitrogen draw back until a sudden drop at the end of June. Translocated nitrogen in C. apiculatum accumulated in large amounts in the peripheral twigs (branching order one) compared to T. sericea, where nitrogen only increased at the end of June in the same location. There was also a corresponding significant change in the carbon:nitrogen ratio in C. apiculatum, especially in the leaves, showing a decrease in palatability as nitrogen was drawn out. The results observed did not become more pronounced in site 3, which had the highest soil moisture content. Soil moisture availability therefore does not appear to influence the degree of nitrogen reabsorption from the leaves. The hypothesis proposed is that deciduous trees use stored nitrogen from their senescing leaves to leaf out earlier gaining a competitive advantage over grasses, which are waiting for nitrogen to be mineralized in the soil with the onset of the summer rain. This study therefore supports the niche separation by phenology hypothesis to explain how these two growth forms coexist in the savanna biome.

The phosphorus (P) uptake capacities and tolerance to high P of three Proteaceae species from acid (Leucadenron coniferum, Leucadendron salignum) and alkaline (Protea obtusifolia, Leucadedndron meridianum) soils in the Cape Floristic Region (CFR) were compared. These species were also investigated as potential candidates for growth on nutrient enriched, post-agricultural soils. In parallel, two crop plant species (Lupinus albus, with cluster roots; and L. angustifolius, without cluster roots) were also compared. The cluster-root forming species (L. albus) was more sensitive to higher P levels and showed toxicity in terms of photosynthesis, efficiency of PSII, transpiration and stomatal conductance. Growth, gaseous exchange and efficiency of photosystem II (as a measure of stress) were determined at 1, 10 and 100 μg P g⁻¹ sand for both lupins and Proteaceae. Kinetics of P uptake (in hydroponics) was determined at a range ( 4 to 2000 μM P) of P concentrations. Phosphorus sensitivity was relatively high in Ld. coniferum as evident from reduced growth, net photosynthetic rate, stomata} conductance and transpiration rates. Protea obtusifolia showed the least sensitivity to increased phosphorus concentrations under acidic and native alkaline conditions. The inability to regulate P uptake rates at elevated phosphorus concentrations and excessive P accumulation were major determinants of P sensitivity. The relatively higher P sensitivity of Lupinus albus compared to L. angustifolius is likely related to the efficient P uptake by cluster roots in the former.

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