HR: 11:05h
AN: C41D-04 INVITED     [PDF]
TI: Carbon and Nitrogen Cycling During the Winter-Summer Transition in a Sub-arctic Heath Understorey Ecosystem
AU: * Grogan, P
EM: groganp@biology.queensu.ca
AF: Department of Biology, Queen's University, Kingston, ON K7L 3N6 Canada
AU: Jonasson, S
EM: svenj@bot.ku.dk
AF: Department of Plant Ecology, University of Copenhagen Oster Farimagsgade 2D, Copenhagen K, DK 1353 Denmark
AB: The close biogeochemical coupling between terrestrial carbon and nitrogen (N) cycles, and the predominant N limitation of plant production in the Arctic indicate that the response of high latitude ecosystem carbon balance to climate change could be strongly influenced by effects on the N cycle. General Circulation Models consistently predict that regional warming will be most rapid at high latitudes during winter, and will be accompanied by increased snowfall. Here, I will describe an experimental investigation of the linkages between winter and summertime biogeochemical cycling in the heath understory of a sub-arctic birch forest. Our approach was to monitor the partitioning of an isotopically enriched 15NH4 addition among microbes, plants, and the soil solution through a series of winter harvests, and a subsequent mid-summer harvest. To investigate the influence of plants on ecosystem N cycling through the winter-summer transition, the isotopic label was added to control plots and to plots from which plants had been removed early in the previous growing season. Our study demonstrates that plants had negligible influence on the seasonal patterns of microbial carbon or N accumulation in the soils of this ecosystem within the time-frame of the experiment. Instead, ecosystem N cycling was dominated by a substantial release of recently acquired N (i.e. 15N label) from soil microbes during the winter-summer transition. Our results strongly suggest that although some of the microbial N released during this period was rapidly acquired by plants, a large proportion was lost as leachates and/or gases. These results will be discussed in the context of the influence of wintertime biogeochemical activities on annual N cycling at the landscape-level, and the potential for increased snowfall to influence N fluxes and net carbon balance in the Arctic.
DE: 0400 Biogeosciences
DE: 4805 Biogeochemical cycles (1615)
DE: 4845 Nutrients and nutrient cycling
SC: Cryosphere [C]
MN: 2003 Fall Meeting