Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 10 2009 10.5194/bg-6-2135-2009 http://www.biogeosciences.net/6/2135/2009/ http://www.biogeosciences.net/6/2135/2009/bg-6-2135-2009.html http://www.biogeosciences.net/6/2135/2009/bg-6-2135-2009.pdf 2135 2144 2009-10-09 Effects of N and P fertilization on the greenhouse gas exchange in two northern peatlands with contrasting N deposition rates M. Lund magnus.lund@nateko.lu.se T. R. Christensen M. Mastepanov A. Lindroth L. Ström Department of Physical Geography and Ecosystems Analysis, Lund University, Sölvegatan 12, 22362 Lund, Sweden Peatlands are important ecosystems in the context of biospheric feedback to climate change, due to the large storage of organic C in peatland soils. Nitrogen deposition and increased nutrient availability in soils following climate warming may cause changes in these ecosystems affecting greenhouse gas exchange. We have conducted an N and P fertilization experiment in two Swedish bogs subjected to high and low background N deposition, and measured the exchange of CO₂, CH₄ and N₂O using the closed chamber technique. During the second year of fertilization, both gross primary production and ecosystem respiration were significantly increased by N addition in the northernmost site where background N deposition is low, while gross primary production was stimulated by P addition in the southern high N deposition site. In addition, a short-term response in respiration was seen following fertilization in both sites, probably associated with rapid growth of nutrient-limited soil microorganisms. No treatment effect was seen on the CH₄ exchange, while N₂O emission peaks were detected in N fertilized plots indicating the importance of taking N₂O into consideration under increased N availability. 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