Date of Award
Doctor of Philosophy
Boreal peatlands play important roles in global C and nutrient cycling. Oligotrophic bogs are naturally nitrogen (N) limited, receiving nutrients only via atmospheric deposition. Increased nutrient deposition, particularly N will almost certainly change the microbiology, biogeochemistry, and C and nutrient balances in bogs. Both primary production and decomposition can be affected, but the net effects of N fertilization are complex and unclear. A three-year N fertilization experiment with 15N double labeled 15NH415NO3 as a tracer was designed to study the effects of increasing N deposition on various N pools (including microbial communities, moss, roots, litter, and aboveground vascular plants) and how these N pools process and retain applied N in four ombrogenous bogs in northern Alberta, Canada. Linear growth of Sphagnum mosses was highly variable. However, both capitulum and stem weight showed increase in weight with N addition, resulting in significant increase of capitulum and stem bulk density with N deposition. Total annual primary production, with both capitulum and stem growth accounted for, doubled from low N deposition plots to high N deposition plots. Microbial biomass N measured by chloroform fumigation-extraction only showed a decrease with N deposition in the first year of the experiment. Fungal biomass declined with N deposition as nutrients are readily available under high N loads, perhaps eliminating the need for help from symbiotic fungi for nutrient uptake. The growth of Sphagnum mosses and microbial communities may have been influenced by drier and warmer growing period during 2005 to 2007. These abnormal climatic events could have masked the effects of N deposition on surface Sphagnum moss and microbial communities. This 15N tracer experiment revealed high retention rates of 15N by moss layers as expected. However, retention efficiency of moss layers declined over time and with increasing N deposition, indicating a leakier system as N deposition exceeds the critical load of Sphagnum moss. Aboveground vascular plants overall benefited from N deposition, but different species responded differently based on the root morphology, rooting depths, and the mycorrhizae associations.
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