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Harvard Forest REU Symposium Abstract 2010
- Title: Exploring the affect of Soil Warming on the level of Nitrate Reductase for Different Tree Species
- Author: Sarah A Gray (Saint Norbert College)
- Abstract:
Nitrogen is the limiting nutrient in a New England Forest, however, with increased soil temperatures and microbial activity, there is more nitrogen available to synthesize amino acids. An eight-year soil warming experiment at Barre Woods in the Harvard Forest has shown that, with increases in soil temperature, the rate of nitrogen mineralization, the conversion of organic nitrogen to ammonium, has also increased. The rate of nitrification, the conversion of ammonium to nitrate, increased as well. I wanted to determine the affect warming could have for different species, on the rate of nitrate reduced into ammonium by nitrate reductase. I measured the activity of nitrate reductase, an enzyme that reduces nitrate to ammonium, in the overstory and understory by sampling leaves from oak (Quercus rubra), maple (Acer rubrum, A. saccharum), ash (Fraxinus americana), and birch (Betula lenta) tree species located in a heated plot 5 degrees above ambient soil temperature and a control plot. A greenhouse experiment was also carried out to measure the influence of added inorganic nitrogen, in varying amounts and ratios of ammonium and nitrate, on leaf and root nitrate reductase activities. Nitrate reductase activity was measured using an in vivo assay. Samples were incubated for 2 hrs in 5 mL of 40 mM KNO3 buffer. Color reagent was added after incubation and samples were read on a spectrophotometer at 540 nm. I found that Q.rubra had higher nitrate reductase activity in the overstory for both May and July than A.rubrum, and F.americana. In the understory B.lenta had higher nitrate reductase activity in June than A.saccharum, A.rubrum, and Q.rubra. Q.rubra in the control plot had higher nitrate reductase activity than the heated plot. Although these trends were shown none of the results were significantly different. The green house results were inconclusive due to the lack of samples and amount of variance.
- Research Category: Soil Carbon and Nitrogen Dynamics
