Influence of topography and moisture and nutrient availability on green alder function on the low arctic tundra, NT

• Main Authors: Black, Katherine Louise, Ms., Baltzer, Jennifer Lynn, Dr.
• Format: Text
• Language: English
• Published: Scholars Commons @ Laurier 2017
• Subjects: tundra shrub expansion; Alnus viridis; transpiration; abiotic limitations; functional traits; resource availability; frost table depth; climate warming; Biodiversity; Biology; Botany; Climate; Ecology and Evolutionary Biology; Environmental Sciences; Hydrology; Integrative Biology; Physiology; Plant Biology; Plant Sciences; Arctic; Northwest Territories; Tundra
• Online Access: https://scholars.wlu.ca/etd/2002; https://scholars.wlu.ca/context/etd/article/3115/viewcontent/KBlack_Thesis_revisions_V2_Sept_11.pdf

The Arctic has warmed by at least 3°C over the past 50 years and this rapid warming is expected to continue. Climate warming is driving the proliferation of shrubs across the tundra biome with implications for energy balance, climate, hydrology, nutrient cycling, and biodiversity. Changes in tundra plant water use attributable to shrub expansion are predicted to increase evapotranspirative water loss which may amplify local warming and reduce run-off. However, little is known about the extent to which shrubs will enhance evapotranspirative water loss in these systems. Direct measures of shrub water use are needed to accurately predict evapotranspiration rates and the associated hydrological and energetic impacts. In addition, it is crucial that we understand the abiotic factors that drive shrub distribution and physiological function to forecast further changes in tundra ecosystem function. Shrubs are expanding in areas that have a higher potential of accumulating moisture, such as drainage channels and hill slopes. Shrub expansion may be limited by variation in water and nutrient availability across topographic gradients. Nevertheless, the associations between shrub function and abiotic limitations remain understudied. To address these knowledge gaps, we measured sap flow, stem water potential, and a range of functional traits of green alder (Alnus viridis) shrubs and quantified water and nutrient availability in shrub patches on the low arctic tundra of the Northwest Territories. Frost table depth was a significant negative driver of sap flow and underlies decreased surface water availability with thaw. This was further supported through significantly lower stem water potential values as the growing season progressed. Shrubs in upslope locations had significantly lower water potentials relative to shrubs in downslope locations, demonstrating topographic variation in shrub water status. Shrubs in channels and at the tops of patch slopes significantly differed in leaf functional traits representing leaf ...