Nitrogen Retention by Sphagnum fuscum in Laboratory Mesocosms: Responses to Experimentally Added NH4+-N and NO3−-N
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To evaluate the effects of increasing atmospheric N deposition on net C and N accumulation in Sphagnum-dominated bogs, we conducted a laboratory mesocosm experiment. Following 45 days of watering with N-free rainwater, mesocosms were exposed to simulated atmospheric N deposition values of 0, 4.14, 8.18, and 12.42 mg N m−2 da−1 over a 108 day period. We quantified N retention from leachate N concentrations and from changes in N contents of the Sphagnum/peat mesocosms. As N loading of simulated atmospheric N deposition increased, so did the net retention of simulated atmospherically deposited N. Our hypothesis of a decrease in N retention efficiency with increasing N loading was not observed. Further, for each N loading treatment, rates of retention of simulated atmospherically deposited N remained constant over time. We did not observe a threshold N deposition below which N would be retained in mesocosms and above which N passed through the mesocosms. Substantially more N was retained in mesocosms that was added in simulated atmospheric N deposition, suggesting an unaccounted for N source, most likely biological N2 fixation. In locations where N2 fixation represents a much greater source of new N to Sphagnum-dominated bogs, as in northern Alberta, Canada, increasing atmospheric N deposition may have a minimal effect on overall net N accumulation in peat.
KeywordsPeatlands Sphagnum Nitrogen Deposition Ammonium Nitrate
Special thanks to Kimberli Scott, Cara Albright, Jim Quinn, and Andrew Rudner for assisting in all aspects of this laboratory study. Funding for the project was provided by a grant awarded to Drs. R. Kelman Wieder, Melanie Vile, and Dale Vitt from the Cumulative Environmental Management Association (grant no. 224940).
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