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UBC Theses and Dissertations

Nitrous oxide emissions, nutrient dynamics and nitrifier communities following fertilization of western hemlock, lodgepole pine and Douglas-fir forests Khan, Amer Ijaz


I explored effects of fertilization on soil N₂O fluxes and underlying soil nutrients using short-term (up to 7 mo.) simulated operational fertilization with urea-nitrogen or nitrogen, phosphorus, potassium, and micronutrients (a N + micronutrients mix) in lodgepole pine, western hemlock, and Douglas-fir forests in British Columbia. The effect on the structure of ammonia- oxidizing bacterial (AOB) communities in the three forest ecosystems was also studied using polymerase chain reaction coupled with denaturing gradient gel electrophoresis (PCR-DGGE). Urea appeared to be rapidly mineralized to ammonium, and nitrification (relative to controls) was only observed in the lodgepole pine site and represented only 0.5% of added nitrogen. Across all sites and treatments, soils were as likely to consume as emit nitrous oxide, and among treatment replicates, rates were never significantly different from zero, with the exception of one efflux of 1.5 μg m-² hr-¹ on the warmest day in the study. I conclude from this pilot study that in acidic, unpolluted (with regard to nitrogen deposition) upland conifer forest soils in western Canada fertilized once or infrequently with urea or ammonium or a combination of nutrients, soil greenhouse-gas flux dynamics are generally not altered over the short-term, with soils remaining neutral with regards to flux of nitrous oxide.

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