x, 166 leaves : ill. ; 25 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1973) from the Dept. of Agronomy, Waite Agricultural Research Institute, University of Adelaide

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The specific activity of the ('32)P labeled sediment-P taken up by submersed macrophytes was shown to be identical to the specific activity of the sediment mobile P, as measured by isotopic dilution. The mobile P therefore represents the sediment-P available to aquatic macrophytes. / The ability to accurately measure the specific activity of the available sediment-P was applied to problems pertaining to the role of macrophytes in P cycling. The relative contribution of water and sediments in supplying P to macrophytes was measured by growing macrophytes in situ, rooted in ('32)P labeled sediments, and with the shoot in free contact with the unlabeled overlying water. Macrophytes grown in mesotrophic and eutrophic sites derived more than 95% of their P from the sediments alone. When grown in a hypertrophic site, the sediments still supplied 70% of the P. / Rates of P release by macrophytes and significance to their periphyton and surrounding phytoplankton were estimated by using fully labeled plants. The periphyton derived only 6.5% of its P form the macrophytes. Myriophyllum released 0.32 ug.g('-1).h('-1) P, most of which being readily available to phytoplankton. / The high vertical mobility of the available sediment-P was demonstrated both by experimental manipulations and direct observations.

This thesis is mainly based on work done in Loch Kilconquhar, Fife, and also to a lesser extent in Loch Lindores, Fife, from March 1979 to March 1981. It discusses the seasonal productivity of the lakes and also the nutrient concentrations, with special reference to phosphate. The overall productivity of phytoplankton in Loch Kilconquhar is high compared with Loch Lindores. The high plankton densities in Loch Kilconquhar during winter were attributed to Diatom species such as Stephanodiscus. Anabaena flos-aquae formed the massive bloom during May 1980 and reached the maximum value of 461.84 +/- 47.02 mg m-2 chlorophyll a in the middle of the month, which was followed by a second blue-green bloom of Aphanizomenon flos-aquae in late summer. The submerged macrophytes such as Myriophyllum spicatum. Zanichellia palustris and Enteromorpha intestinalis grew well on the west side of the loch after the decline of the Anabaena bloom in July 1980, The value of sedimentary chlorophyll reached a maximum of 13.96 +/- 2.04 mg m in late April 1980. The high concentration of Soluble Reactive Phosphate (range: 0.004 - 0.780 mg/l PO4-P) and Nitrate-nitrogen (range: 0.980 - 2.350 mg/l NO3-N) also indicates that Loch Kilconguhar is a nutrient-rich freshwater loch. It is interesting to note that the soluble phosphate is exceptionally high compared with other freshwater lochs in Scotland. There are several possible reasons for this high concentration. Firstly, drainage from an agricultural area may contain much phosphate. However, the inflow in this case has little soluble phosphate but is high in soluble nitrate. Secondly, decomposition of organisms, notably phytoplankton blooms and macrophytes, may contribute to the high concentration of phosphate; these organisms, however, must in turn obtain their phosphorus from water and sediment. The third possibility, and probably the most important, is the nutrient release from the loch sediment. In a laboratory experiment, it was shown that when the dissolved oxygen dropped below 1 mg/1 and the redox potential E7 fell below 240 mVolt, substantial amounts of nutrients, particularly phosphate, were released into the overlying water. The primary source of nutrient in Loch Kilconquhar is the phosphorus-rich excrements of the large wildfowl population and also gulls on the loch. The results show that one g of fresh duck dropping has a mean content of 4170 +/- 350 mg/kg total phosphate and one g of gull dropping has 5072 +/- 748 mg/kg total phosphate.

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A two-year fertilizer study on a mature vineyard of Vita vinifera, C. V. Cabernet Sauvignon and Sauvignon blanc, has been conducted on White House sandy loam (fine, mixed, thermic Ustollic Haplargid), at Page Ranch, International Agricultural Center. Furthermore, eleven different varieties grown at Page Ranch and treated with different levels of nitrogen fertilizer were tested for total P content in plant tissue and NO₃-N. Moreover, in another site with similar soil, a Cabernet Sauvignon grown at the Vina Sonoita Vineyard was treated with both soil and foliar applications of P fertilizer, and was tested for total P content in plant tissue. Soil phosphorus (P) fractions of the White House soil were determined in order to evaluate the various forms of soil P and determine the most important form which contributes most to the availability index. The objectives of this study were to study the various inorganic P forms of White House soil, compare two methods of extracting available P (Olsen and Bray P.), and examine the relationships between soil pH, extractable Al, Fe, Mn, and Zn with the availability index of soil P. Furthermore, the effect of P rates and placement on the P status of plant tissue, grape yield, wine quality and petiole-P to blade-P ratio had been investigated. Three different placements of surface, 25 and 50 cm depth at rates of 88 g of P and 80 g of N per vine, were in RCB design in 1987. In 1988, three P rates of 0, 88, and 176 g of P and 207.5 g N per vine, and the two mentioned varieties CS and SB were arranged in RCB design with factorial type. The results showed that placements did not have a significant effect of P status in plant tissue and grape yield. Yet grapes showed a significant response to P fertilizer in terms of increasing P content in plant tissues and grape yield. Petiole P to Blade P ratios were calculated for the CS, and SB grown at Page Ranch, as well as for CS grown at Sonoita vineyard. This ratio is a good indicator for diagnosis of P status in a given vineyard. Nitrogen stress had its clear and profound effect on P content of grape petioles.

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Bibliography: leaves 169-193. This study investigated whether both S. Calospora and Glomus sp. "City Beach" WUM 16 both increase the rate of transfer of phosphate (P) to the plant Allium porrum, and whether the addition of P to the soil has any effect on the uptake rates. The main experiment compared the fungi under two P levels in soils. It was found that in soil with no added P, S. calospora depressed plant growth in the early stages, but was increased in later harvests. G. sp. "City Beach" increased plant growth throughout. In soil with added P, both sets of plants produced growth depressions at early stages. The effect on growth due to mycorrhizal symbiosis was greater in plants grown in soil with no phosphate added. There were no significant differences between the two fungi with reflexes of P across the interfaces. There were however temporal differences. The isolate of S. calospora did promote a positive plant growth response in A. porrum and transfer P to the plant. Mycorrhizal arbuscules were examined and visualised using Laser Scanning Confocal Microscope and 3D reconstructions performed. This allowed the surface area and volume of the arbuscules to be quantified in order to investigate differences between the fungi.

Graduation date: 1990

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