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Trembling aspen (Populus tremuloides) leaf litter decomposition under simulated nitrogen and sulfur deposition in a mixedwood boreal forest
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- Author / Creator
- Wang, Qi
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As one of the largest oil sands deposits in the world, the Athabasca oil sands region (AOSR) has generated and released large amounts of nitrogen oxides (NOx) and sulfur dioxide (SO2) to the atmosphere and the surrounding area. Long-term N and S deposition at elevated rates can cause soil acidification, decrease forest productivity, and change plant community composition. Litter decomposition is an important component of nutrient and carbon (C) cycling in terrestrial ecosystems which relate to forest productivity and greenhouse gas emissions. Litter decomposition rates are affected by many factors such as climate, litter chemistry, N and S addition, soil properties, and litter enzyme activities. To better understand how N and S deposition impacts litter decomposition in a boreal forest, I conducted laboratory (100-day) and field (18-month) experiments in this study. Litter and forest floor (F and H layers, after removing current litter layer) samples were collected from a mixedwood boreal forest located about 100 km southeast of Fort McMurray, northern Alberta. Litter C, N and S concentrations were determined using an elemental analyzer. Litter lignin concentration was analyzed by measuring absorbance at 280 nm following acetyl bromide digestion. Other elemental concentrations including calcium (Ca), magnesium (Mg), aluminum (Al), and manganese (Mn) were determined using an ICP-MS method. The MBC and MBN concentrations from the forest floor were determined using a fumigation-extraction method. Extracellular enzyme activities involved in C, N and S cycling were analyzed using fluorimetric and colorimetric methods: β-1, 4-glucosidase (GLU, enzyme classification (EC) EC 3.2.1.21) for C, β-1, 4-N-acetylglucosaminidase (NAG, EC 3.2.1.14) for N, and arylsulfatase (ARS, EC 3.1.6.1) for S. In the laboratory study, 10 years of N and S deposition changed trembling aspen (Populus tremuloides) litter chemistry and forest floor microbial properties. Cumulative CO2 emission (Ccum) from the litter was negatively correlated with C/N and lignin/N ratios in litter (P < 0.05), but not with forest floor microbial properties (P > 0.05). This laboratory study provided evidence that N and S addition can enhance litter decomposition through changed litter chemistry, suggesting that C cycling in the boreal forest ecosystem in the oil sands region can be significantly affected by long-term N and S deposition. However, these results need to be testified in the field. In the field study, N and S addition did not directly affect litter decomposition rates (P > 0.05) (Experiment I), and nutrient-induced changes in litter chemistry did not regulate litter decomposition rates under N and S addition (P > 0.05) (Experiment II). Litter N exhibited an immobilization phase followed by an initial release phase, while an initial leaching phase occurred followed by an immobilization phase until the end of study for S in both experiments. And extracellular enzyme activities in litter did not correlate with litter decay constants. To fully understand the effect of N and S deposition on litter decomposition, a long-term decomposition study is recommended.
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- Graduation date
- Fall 2017
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.