Globally, peatlands cover 3-4 % of the Earth?s land surface, yet they store 25-30% of the world?s soil carbon (C) and 9-16% of the world?s soil nitrogen (N) in peat. The cycling of C, and in particular the strength of the bog C sink, changes dramatically and predictably as a function of time since fire. However, understanding of how N cycling changes in bogs as a function of time since fire is unknown. This is a Rapid Response Research (RAPID) award to support a project to study carbon (C) and nitrogen (N)cycling at Utikuma Bog, in western Alberta Canada. The site represents an unique opportunity for research on linked bog N and C cycling in light of the recent wildfire activity which decimated the site, the historically low atmospheric N deposition (<1 kg/ha/yr), which anchors the site as a global end-member in the spectrum of atmospheric N deposition, and because of the large stores of C found in Canadian peatlands.
Peatlands of the boreal forest are vital to global terrestrial N and C balances, and the vulnerability of the large amounts of N and C stored in peat deposits has both science and policy implications. With RAPID funding to initiate investigations at the burned Utikuma Bog, this project is expected to transform current understanding of bog N cycling, which has largely ignored the potential ramifications of fire in boreal bogs of western Canada. The project will also support one M.S. student at Villanova University and one undergraduate lab/field assistant.
Peatlands (bogs and fens) are widely recognized for their substantial quantities of carbon (C) stored as organic soil (peat), which can accumulate to thicknesses of 5 meters or more. Globally, peatlands contain 25-30 % of the world’s soil C, which is especially impressive given that these ecosystems cover only 3 % of the earth’s land surface. Our work focuses on boreal, continental, western Canada (Alberta, Saskatchewan, Manitoba), where peatlands cover 365,000 km2 and store 42 Pg (1 Pg = 1015 g) of C. With prior NSF support, we revealed that although this region’s peatlands currently continue to function as a net sink for atmospheric C, converting CO2 into peat, wildfire diminishes the strength of the regional C sink. Fire oxidizes vegetation and peat to CO2, which is immediately released to the atmosphere. Also, just after fire, CO2 release from ongoing decomposition of the peat exceeds net CO2 uptake by vegetation (which is mostly killed by fire), such that peatlands function as net sources of CO2 until about 20 years after fire when vegetation has sufficiently recovered. With NSF RAPID support, we have shifted our focus to nitrogen (N) cycling and the linkages between C and N cycling, both as a function of time since fire. In addition to storing C, peatlands store 9-16% of the world’s soil N. Despite the importance of peatlands as long-term N sinks, how the various components of the N cycle change after fire is poorly understood. Our research ultimately relies on a chronosequence of bogs that differ in time since the most recent fire. In May of 2011, one of our long-term research sites, Utikuma Bog (Alberta), burned, providing a unique opportunity to initiate research on C and N cycling immediately after fire. With NSF RAPID support, at Utikuma Bog, we established 6 transects, each with 4 replicated 3-m x 6-m plots, receiving no water (controls), or the equivalent of 0, 10, and 20 kg/ha/yr of N, applied as NH4NO3 solutions using backpack sprayers over 8 application events between May and September. A weather station surrounded by a solar-powered electric fence was installed, along with 10 mixed-bed ion exchange resin collectors (5 in the open and 5 beneath black spruce canopies) for quantification of ammonium and nitrate inputs to the bog by atmospheric deposition. Permanent collars were installed in each plot, one in a hummock and one in a hollow, for net CO2 flux measurements. Cranked wires, 50 per plot, were set for the measurement of Sphagnum moss net primary production. Net nitrogen mineralization was quantified using the buried bag method. Measurements of biological N2-fixation were initiated in all plots. We have shown that biological N2-fixation, previously thought to be unimportant in bogs, represents the major input of new N to mature bogs greater than 50 years since fire). However, with NSF RAPID support, we have shown that at the burned Utikuma Bog, biological N2-fixation is minimal. The microorganisms that fix N2 thrive in the moist living Sphagnum moss layer; the dead and/or severely desiccated mosses after fire do not offer an environment favorable for N2-fixers. How N2-fixation changes along a time-since-fire bog chronosequence is a part of our ongoing research. We quantified N mineralization and nitrification, the microbial processes by which organic N in peat is converted to inorganic, water-soluble ammonium and nitrate. We have shown that at Utikuma Bog, both net mineralization and nitrification are much higher than at one of our mature bog sites. The elevated rates at Utikuma Bog are associated with higher concentrations of ammonium, nitrate, and dissolved organic nitrogen in peat pore water, and possibly a dominance of bacteria over fungi. Almost all bog vascular plants have mycorrhizal fungal symbionts, whose activities are likely low after fire because at least the aboveground parts of the vascular plants have been burned. We also have focused on linkages between C and N cycling, quantifying net CO2 fluxes at Utikuma Bog using closed chambers and CO2 measurements with infrared gas analyzers. In both 2011 and 2012, hollows were a much stronger net source of CO2 than hummocks (Sphagnum fuscum-dominated hummocks retain moisture much better than S. angustifolium-dominated hollows; hence the living moss layer in hollows burns much more readily than in hummocks). In both years, there was a general pattern of a diminished net CO2 efflux in hummocks with N additions of 10 or 20 kg/ha/yr, suggesting that N addition enhances C balance recovery. The Masters thesis research of 2 graduate students was supported by the RAPID award. Five undergraduate assistants, 2 graduate students, and 3 technicians contributed to the field and/or lab work associated with the RAPID project. At this date, one nontechnical article was published (Nitrogen cycling immediately after fire in an Alberta bog, International Innovations 40, 2013), and one conference presentation has resulted from the RAPID award.
