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The availability of phosphorus from the anoxic hypolimnia of lakes to epilimnetic plankton was investigated by experimental studies on eight lakes in Ontario and Quebec. Availability was determined with a short-term bioassay based on the standardized retardation of planktonic uptake of phosphorus tracer in the presence of orthophosphate; availability was also estimated by SRP (soluble reactive phosphorus) analysis, since approximately 90% of SRP was available in anoxic waters. / Iron concentrations were high in some hypolimnia, but should become diluted after mixing with surface water. When iron concentrations after mixing exceeded 0.20 mg/L, aeration lowered availability and SRP. Therefore, samples from anoxic hypolimnia were kept anoxic. The fate of hypolimnetic phosphorus at turnover was studied by construction of a budget for SRP, total phosphorus, particulate iron containing phosphorus and particulate biological phosphorus at fall turnover in Lake Magog. Despite high concentrations of hypolimnetic iron, only 30% of the upwelling hypolimnetic phosphorus combined with iron after complete mixing, 30% was incorporated into biomass and 38% stayed potentially available as SRP. / In two lakes, hypolimnetic iron was undetectable hydrogen sulfide concentrations were high. H(,2)S interfered with the SRP analysis and poisoned plankton. After degassing, routine SRP analysis was possible, and availability was close to 100%. Iron and H(,2)S interference in the SRP analysis were circumvented by degassing or by maintaining anoxia. A simpler method, the analysis of TRP (total reactive phosphorus) after aeration, was developed which analyses SRP quantitatively in anoxic waters.

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Interspecific competition for phosphorus was studied in continuous lake water cultures of phytoplankton communities from Lake Memphremagog, and its outcome shown to depend primarily on the size of the competitors. Comparison of the activity of the inducible enzyme alkaline phosphatase between the lake and cultures operated at various dilution rates (0.06-0.93 day('-1)) established that in situ phosphorus limitation rarely depressed average community growth rates much below 0.6 day('-1). Growth rates under comparable, or even more severe (0.2-0.3 day('-1)) limitation in culture decreased significantly with increasing cell size. Phosphorus uptake kinetics and cell quotas measured by track autoradiography on the competing species showed that biomass and quota-specific uptake rates varied inversely with cell size in highly significant allometric regressions, correctly predicting that competitive outcome should depend on size. Substituted in a variable internal stores model of phosphorus limited growth, the allometric functions for uptake, cell quota, and maximum growth rate correctly predicted observed growth rates except in competition much stronger than natural (D = 0.06-0.2 day('-1)). Failure of the model to encompass cell senescence and death due to severe nutrient stress appeared to account for the discrepancy. Neither the absolute difference in growth rates due to cell size nor the direction of selection among the naturally co-occurring species varied systematically with the intensity of competition, indicating that spatio-temporal variation of limiting phosphorus supply in nature is unlikely to directly select the size or taxonomic composition of phytoplankton communities.

Development and functioning of arbuscular mycorrhizal (AM) symbiosis in the soil-plant system are required in sustainable agriculture. AM development of maize genotypes and uptake of nutrients as influenced by soil P levels were studied. Several experiments were conducted both in the greenhouse and in the field. / In greenhouse trials, pasteurized substrates were inoculated with Glomus intraradices as mycorrhizal treatments. Mycorrhizal development varied widely among maize hybrids and inbreds. Leafy normal stature (LNS) had the highest root colonization and shoot:root ratio and was the most responsive to AM fungi. Mycorrhizal development was generally reduced at high soil P and micronutrient levels. The percentage of root colonization was correlated with the ratio of plant tissue N/P only when soil N level was intermediate. Mycorrhizal plants increased uptake of Zn and Cu only at low P and low micronutrient levels, but decreased Mn uptake at higher micronutrient level. / In field trials, soil fumigation was used to eliminate AM fungi in control plots. Again LNS was most responsive to indigenous AM fungi, closely followed by Non-leafy normal stature (NLNS). Mycorrhizae increased uptake of K, Ca and Mg only when these nutrients and available P were low in soil. Correlations between extraradicular hyphae and plant concentrations of K, Ca and Mg suggested that uptake of K was more dependent on extraradicular hyphae than uptake of Ca and Mg. Total P uptake was higher in plots where the AM symbiosis was not repressed, but soil available P was not always reduced. / There is potential for development of mycorrhiza efficient maize hybrids performing well under low input management in sustainable agriculture.

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Fertilizer P accumulates in soils, with potential for movement to waterways, causing eutrophication. Fertilizer P reactions in monoculture corn (Zea mays L.) production over time will determine environmentally sound soil management practices. Soil P changes over time were determined on a Chicot sandy clay loam (Grey Brown Luvisol) and a Ste. Rosalie clay (Humic Gleysol). Fertilizer P was added at 44 and 132 kg P ha$ sp{-1}$ and to the Chicot soil only, manure containing 60 kg P for the first five years. Mehlich-3 (M3) extraction, soil P fractionation, $ sp{31}$P NMR analysis, P in leaching water, and path analysis were measured. Added P increased M3 P more when manure was also added, and in clay soils. To increase M3 P by 1 kg ha$ sp{-1}$ required from 3.6 to 8.1 kg ha$ sp{-1}$ fertilizer P, and when "net" fertilizer additions were used, fertilizer required was from 1.8 to 5.3 kg P ha$ sp{-1}.$ Moderately labile organic P (Po) decreased at 0 added P. With P at the rate of plant removal, inorganic (Pi) and Po fractions were unchanged. Excess P increased labile P and resistant P through moderately labile Pi. More P remained in labile Pi fractions when manure P was added, or in the soil with the higher clay content. Soil organic P levels increased upon fertilization only in the sandy loam soil. Labile and moderately labile Po could be estimated using monoester phosphate values determined by $ sp{31}$P NMR. Inorganic P values in gravitational water increased above 0.05 mg P L$ sp{-1}$ when soil labile Pi increased above 108 mg kg$ sp{-1}$ in the sandy loam soil and 69 mg L$ sp{-1}$ in the clay soil. Thus soil P movement was related to inorganic P additions. Increased fertilizer P did not increase organic P leaching losses. Fertilizer P in corn production may result in groundwater eutrophication.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1982. / Bibliography: leaves 169-177. / Microfiche. / xvi, 177 leaves, bound ill. 29 cm