Phosphorus limitation controls rates of biological N2-fixation in boreal peatlands
Abstract
N2-fixation, once thought to occur at negligible rates in pristine boreal peatlands, has recently been demonstrated to be the dominant input of nitrogen (N) to these ecosystems. The controls of biological N2-fixation in pristine boreal peatlands are not well understood, but limitation of the nutrients molybdenum (Mo) and phosphorus (P) may play a key role. Because the enzyme nitrogenase requires molybdenum-containing cofactors to function, biological N2-fixation may be limited by the trace metal molybdenum. Recent studies have shown that Mo limits nitrogen fixation rates in tropical soils. P availability may also be important in regulating N2-fixation rates; N2-fixation is a P-intensive process because the nitrogenase enzyme is rich in P, and P is likely to be the most limiting nutrient to boreal peatland productivity, next to N. In this study, we examined the role of Mo and P limitation in controlling rates of biological N2-fixation in boreal peatlands. We applied Mo and P nutrient amendments equivalent to 5 mg m-2 yr-1and 10 kg ha-1 yr-1 respectively, both alone and in combination, to fifteen 0.36 m2 plots in a pristine Alberta fen throughout the summer 2013 growing season. We periodically assessed N2-fixation rates in Sphagnum angustifolium moss samples using the acetylene reduction assay with subsequent calibration using 15N2. We found a significant overall treatment effect (F3,44=15.62, p<0.0001). A posteriori analysis using Tukey's HSD indicates that N2-fixation rates were significantly higher in plots receiving P additions relative to control plots. However, Mo additions had no effect on N2-fixation rates. These results indicate that P, not Mo, availability is dominant in controlling rates of biological N2-fixation in boreal peatland ecosystems.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.B43E0548D
- Keywords:
-
- 0469 BIOGEOSCIENCES Nitrogen cycling;
- 0497 BIOGEOSCIENCES Wetlands