NWT RESEARCH DATABASE

Tags: biology, soil, plant distribution, vegetation, climate change, environmental change, snow accumulation, tundra ecosystems, nutrient levels, nitrogen

Objective(s): To substantially advance the understanding of how Canadian Arctic tundra ecosystems function, and therefore how they are likely to be affected by perturbations such as climate change, resource development and extraction, and atmospheric pollution.

Project Description: The goal of this research over the next five years is to substantially advance the understanding of how Canadian arctic tundra ecosystems function, and therefore how they are likely to be affected by perturbations such as climate change, resource development and extraction, and atmospheric pollution. Specifically, the research team will focus on the impacts on vegetation due to warmer summer temperatures, deeper winter snow, increased nutrient availability and changes in herbivory. This research will involve sampling of small pieces of soil and vegetation from an area within a 5 km radius of the Daring Lake Research Station, as well as from the small experimental manipulations (fertilizer plots (5 x 7 m), snowfences (15 m), greenhouses (~2 x 5 m) and fenced exclosures (20 x 20m)) that we have set up within an ~3 km2 area close to the station. SPECIFIC RESEARCH QUESTIONS, APPROACHES AND ACTIVITIES Ongoing activities Q1. What is the significance of biogeochemical processes during winter and spring-thaw to overall annual nitrogen cycling in tundra ecosystems? This question will be addressed through long-term manipulations of snow depth (fences) and nitrogen availability (using additions of the stable isotopic tracer 15N in late Fall) at Daring Lake. The research team will study the effects of deepened snow on winter and springtime nitrogen availability to plants, as well as soil solution and microbial pools, and run-off/leachates in the subsequent spring and summer seasons. Relative partitioning amongst microbial and vegetation components including shrubs will be determined using the 15N label. Q2. What are the principal controls on the functioning of common tundra ecosystem types, and how are they likely to be affected directly and indirectly by climate change? The principal researcher has initiated (along with my colleagues Drs. Lafleur and Henry) and now maintain a series of strategic long-term experiments in birch hummock tundra at Daring (factorial N and P additions, greenhouse warming and drying, low level and isotopic nitrogen additions, snowfences, and partly fertilized fenced exclosures) to investigate the response dynamics and interactions between various factors that are expected to be altered by future climate (e.g. snow accumulation, vegetation distributions). These experiments will provide the essential foundation to characterize many of the major controls on the functioning of an ecosystem-type that extends across a large section of the Canadian low Arctic, and to contrast the findings with those from other major arctic research sites (e.g. Toolik Lake in Alaska, and Abisko in Sweden). Q3. Are shrubs becoming more abundant in the Canadian low arctic? Although recent shrub density increases and expansion have been well characterized in Alaskan tundra, the research team currently know very little about corresponding vegetation change in northern Canada. The research team established ten longterm shrub monitoring plots (100 m2) at Daring in 2006 and made detailed maps indicating shrub density, height, and branching architecture. In addition, at a larger scale, in collaboration with the Government of the Northwest Territories, the research team will compare and ground-truth IKONOS high resolution satellite images of the Daring region from 2000 with 2010. Q4. What is the outcome of tundra plant-soil microbial competition for nitrogen over the 5-10 year time scale? When nitrogen is added to tundra, soil microbes tend to accumulate most of it within days to weeks. Over five year and longer time scales, continued large nutrient additions result in enhanced plant uptake, presumably because microbes are ‘saturated’ and no longer competing. Although these studies have been interpreted as indicators of potential impacts of increased nutrient availability associated with faster decomposition due to climate warming, actual rates of increase are likely to be much lower. If so, will plants gain access to the enhanced N, or will they be outcompeted by ‘hungry’ (i.e. unsaturated) microbes? To investigate the medium term temporal dynamics of plant-microbial competition for moderately enhanced nitrogen availability, the research team have three experiments (single large additions; ongoing low level additions; and 15N additions) and will monitor the plots over the next five years. New activities Q.5. What are the impacts of herbivory on vegetation production and composition, and how might these impacts be altered as a result of climate change. The research team will use the exclosure plots described above to investigate how herbivory from caribou and small mammals interacts with vegetation growth and composition. Specifically the research team will measure plant growth and leaf tissue chemistry inside and outside the exclosures to characterize the effects of herbivores, and to investigate if plant leaf chemistry (secondary metabolites) alters when herbivory is excluded. Copies of the publications the research team achieve will be forwarded to the Aurora Research Institute, and the Division of Environment and Natural Resources, Government of NWT for distribution to the communities. The research team will participate in the Daring Lake Science Camp each year, if any of the group are present at that time. The research team anticipate recruiting at least one local student from the science camp or locally from Yellowknife to stay on and help with the vegetation and soil sampling. The fieldwork for this study will be conducted from July 4, 2013 to September 20, 2013.