PARENT SESSION
Contributed Oral Session 57: Polar and Alpine Ecology: Carbon and Nutrient Dynamics
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 513 E, Level 5, Palais des congrès de Montréal
Plant and microbial utilization of nitrogen and phosphorus in Arctic freshwater sedge meadows.
Edwards, Kate1, Jefferies, Robert1, 1 University of Toronto, Toronto, Ontario, Canada
ABSTRACT- Primary productivity in Arctic and sub-Arctic ecosystems is typically limited by nitrogen (N), phosphorus (P) or both. However, the utilization of N and P by plants and soil microbes is poorly understood in these systems, where seasonality plays a dominant role in biogeochemical processes. We examined annual N and P cycling dyanamics in fresh-water sedge meadows near Churchill, Manitoba, Canada. Two types of meadow were compared, both dominated by Carex aquatilis but differing in above-ground productivity, soil water content, and redox potential. Experimental plots were treated with N and P additions in a replicated full-factorial design. Various parameters including microbial and plant biomass, phosphatase activity, net N-mineralization, and soil inorganic, microbial, and plant N, P, and carbon fractions were quantified throughout the summer and fall from melt until early winter in late November. C. aquatilis growth was found to be co-limited by N and P in both low and high productivity areas. Levels of soil exchangeable ammonium and nitrate were low, with a substantial pulse followed by a rapid decline of exchangeable soil ammonium between June and July (at melt). Microbial activity fluctuated seasonally, decreasing during the early summer and increasing during the fall, similar to previous findings from alpine systems. Alkaline phosphatase activities were accordingly high in late fall. These results demonstrate the role of seasonal events in nutrient cycling, in a system where both N and P limit plant growth. Characterizing these nutrient dynamics is critical to predicting the effects of N and P availability on higher trophic levels, as herbivores such as lesser snow geese (Chen caerulescens caerulescens) forage on sedges. In the P-limited system studied here, herbivores may experience P-deficiency due to low-quality forage, leading to compromised growth rates of individuals, and negative population effects.
Key words: nitrogen, phosphorus, nutrient cycling, arctic soils