Phosphorus is the main limiting nutrient for plant growth in large areas of the world and the availability of phosphorus to plants and microbes can be strongly affected by soil properties. Even though the phosphorus cycle has been studied extensively, much remains unknown about the key processes governing phosphorus availability in different environments. In this thesis the complex dynamics of soil phosphorus and its availability were studied by relating various phosphorus fractions and soil characteristics to microbial respiration kinetics. The soils used represent a range of aluminium, iron, carbon and total phosphorus content, and were located in four different biomes: subtropical forest, warm temperate forest, boreal forest and tundra. The results showed that NaOH extractable phosphorus, a fraction previously considered to be available to plants only over long time scales, can be accessed by microbes in days or weeks. Microbial phosphorus availability was not related to aluminium or iron content in any of the studied systems, not even in highly weathered soils with high aluminium and iron content. This is in contrast with other studies of soils with high sorption capacity and shows the variability of factors that govern phosphorus availability in different environments. In the boreal forest chronosequence, no difference could be seen with age in total phosphorus content or concentrations of occluded phosphorus forms. However, there were lower concentrations of labile phosphorus forms in older systems, which were correlated with a decrease in microbial respiration. This was most likely related to organic matter quality in the system, and not to geochemical factors. Phosphorus availability was linked to differences in topography (water regime) and vegetation in the tundra ecosystems. The results suggest that the availability of phosphorus, both for microbes and plants, was lower on the meadow vegetation sites compared to the two types of heath vegetation. Many factors are important for phosphorus availability in soils, but these results suggest that microbes can access less available phosphorus if not restricted by carbon, and this may be important in regard to forest management practices as well as effects of environmental change.

[Truncated abstract] Acidic mine lakes are formed as a result of the oxidation and dissolution of metal sulfide minerals and are primarily characterized by low pH values of 2 – 4. Many strategies for the bioremediation of acidic mine lakes depend on the alkalinity generation capabilities of microbial ferric and/or sulfate reducing bacteria. However nearly all mine lakes are oligotrophic, with very low concentrations of available organic carbon and nutrients; all required for healthy microbial growth. There is also an unusual class of mine lakes characterized by low concentrations of organic carbon and also very low concentrations of dissolved iron and sulfate. Our ability to promote microbial activity in these systems is especially challenging. This study focuses on one of these systems, Lake Kepwari, a coal mine lake in Western Australia. Numerical modeling of remediation strategies is an efficient way of testing scenarios prior to expensive in-field trials. However such modeling relies on good descriptions of microbial processes, including kinetic parameterizations of ferric and sulfate reduction. There has been little research to date on the study of kinetic parameterizations of the chemical and biological alkalinity generation in acidic mine lakes. The objectives of this thesis were to investigate the viability of microbial ferric and sulfate reduction in an ultraoligotrophic, acidic mine lake, to assess the impact of these microbial processes on water quality and to parameterize the Dual Monod kinetics of neutralization under dual limitation conditions. Molecular analyses including most probable number, DNA extraction, polymerase chain reaction, polymerase chain reaction – denaturing gradient gel electrophoresis were used to examine the microbial communities in the lake sediments. ... The Monod maximum specific microbial growth rates with respect to dissolved organic carbon and ferric, and as determined in batch experiments, were 0.07 ± 0.01 and 0.048 ± 0.02 day-1, respectively, and their corresponding Monod half saturation constants and were 14.37 and 5.6 mmol L-1. The Monod maximum consumption rates under ferric and OC limitation were also estimated. The Monod maximum specific microbial growth rates with respect to dissolved organic carbon and sulfate, , and were 0.05 ± 0.01, 0.08 ± 0.01 and 0.07 ± 0.02 day-1, respectively, and their corresponding Monod half saturation constants, and were 75.5, 131.8 and 10.2 mmol L-1. The Monod maximum consumption rates under sulfate and OC limitation were also estimated. The results of this study suggest that strategies for the remediation of ultraoligotrophic, acidic mine lakes may rely on microbial ferric and sulfate reduction, however additions of both organic carbon and sulfate/ferric are essential. These results can be immediately applied to mesocosm studies in outdoor enclosures and to the management of acidic mine lakes. Furthermore, this thesis has provided a new, valuable understanding on the Dual Monod kinetic parameterizations of neutralization for an ultraoligotrophic, acidic mine lake environment. These parameterizations are essential for the lake ecological models that will be used to investigate remediation scenarios for acidic mine lakes.