The role of temperature in carbon and nitrogen mineralization from selected arable Nova Scotia soils

This thesis focuses on the effects of soil management history and temperature on C and N mineralization. A preliminary field study indicated that N uptake by a crop was related to variability in substrate quantity and quality, and environmental factors. Further experiments in soil microcosms investigated the effects of soil temperature and management history on net C and N mineralization using soils from a fertility experiment with and without a history of manure application. Microcosms were incubated at 5, 15, 25 or 35°C, with and without the addition of 14C-labelled wheat. For native C and N, and 14C, the size of the substrate pool estimated using the first-order model of decomposition changed with temperature, contradicting one of the key assumptions of the first-order approach to modelling net C and N mineralization in soils. The temperature response of native C and N mineralization differed in the non-amended microcosms, with a substantial increase in the rate of N mineralization relative to C mineralization between 5 and 15°C. Microbial community structure changed with temperature, with distinct fungal communities present at 5°C. The size of the microbial biomass declined with increasing temperature, and metabolic quotients were also highest at 35°C. A further study using 13C-labelled wheat indicated some differences in the accessibility of the wheat C due to management history at the coldest incubation temperature. The use of DNA-SIP along with density gradient centrifugation was used to separate wheat C from native C metabolizing communities, with a trend towards declining diversity with increasing density within the fungal population.;Current soil C and N models that include empirically-derived temperature response functions, already implicitly include temperature effects on biological parameters. In most cases these effects were not shown to interact with soil management history in these experiments, providing no evidence to support the more explicit inclusion of biological parameters, such as microbial community structure and size, in improved models. While measurement of biological parameters provided useful insights into the mechanisms behind variations in estimates of substrate pool size at different temperatures, evidence was not provided for the inclusion of biological parameters explicitly within soil decomposition models.