Relationships between plant productivity and soil conditions in alpine tundra of southern Yukon Territory, Canada
Climate change is predicted to significantly alter ecosystem functioning and species distributions across the globe. Arctic and alpine areas are experiencing a faster rate of temperature increase as compared to other environments, and are expected to be highly sensitive to climate change. Current research and modeling predicts changes in plant productivity and ultimately northward biome shifts; however, the exact mechanisms that will drive these changes are still uncertain. Previous studies suggest that changes in soil temperature, not air temperature, regulate many aspects of plant productivity in cool environments through the indirect effects of temperature on nutrient availability. This research focused on how soil properties are linked to plant productivity in northern environments, through an assessment of soil temperature, soil nitrogen, soil moisture, snow depth, and plant productivity near Whitehorse, Yukon, Canada. The effects of soil warming on soil nitrate and ammonium concentrations, and plant growth, and the effects of ammonium-nitrate fertilization on plant growth, were assessed in an experimental warming and fertilization study. Relationships between mean soil temperature, soil temperature coefficient of variation, total soil nitrogen, soil moisture, snow depth, and plant productivity were examined through field observations along a natural vegetation gradient. In both of these studies I found that plant productivity showed the strongest response to soil nitrogen. In the experimental study, the only species to respond to the experimental manipulations, Carex microchaeta, showed the strongest response of leaf length to warming + fertilization and a stronger response to fertilization than warming, and in the gradient study, soil nitrogen showed the strongest patterns of covariance with plant productivity. Nitrogen having the strongest relationship with plant productivity, and leaf traits showing the greatest responses to fertilization, was consistent with the theory that nitrogen availability is the strongest factor limiting plant growth in both arctic and alpine tundra plants. I found that soil moisture had the second strongest correlation with plant productivity in the gradient study, and that soil moisture was also strongly correlated to total soil nitrogen levels. Tall shrubs were consistently different from other vegetation types, with increased productivity as compared to other vegetation types at all levels of environmental factors in the gradient study, and the strongest relationship with tall shrub habitat productivity was not soil nitrogen but mean soil temperature. While I could not infer causality from the descriptive study of the landscape, the strong relationship of soil moisture with both plant productivity and soil nitrogen indicated that changes in precipitation resulting in increased soil moisture could be an important determinant of future plant productivity at this alpine site. However, my results also suggested that increasing temperatures will result in tall shrub habitats showing greater increases in productivity than other vegetation types. The positive correlations between most environmental factors and plant productivity indicated that increases in plant productivity could be expected with the environmental changes that have been predicted with climate change. Increases in temperature, precipitation causing increased soil moisture, and nitrogen availability will likely result in higher plant productivity at this alpine site, but the relative increases in plant productivity between different plant groups will depend on which environmental factor experiences the greatest changes.
climate change, plant productivity, soil temperature, nitrogen, alpine tundra
Master of Science (M.Sc.)