409 0038-075C/03/16806-409–420 June 2003 Soil Science Vol. 168, No. 6 Copyright © 2003 by Lippincott Williams & Wilkins, Inc. Printed in U.S.A. P EATLANDS are unique among the world’s ecosystems in that production is greater than decomposition, resulting in long-term nutrient sequestration in recalcitrant organic material. As global C stores, peatland soils and changes in their processes become important in the analyses of global geochemical cycles. Global changes such as precipitation regimes and nutrient and acid deposition will all have marked effects on these pools of soil C. Differences in wetting and drying subjects the peat to changes in aerobic versus anaerobic conditions. Increases in atmo- spheric deposition alter nutrient status as well as soil pH. Given the myriad of potential changes, it is important to understand what limits the de- composition/mineralization processes inasmuch as mineralization is often the rate-limiting step that governs nutrient turnover, CO 2 release, and subsequent productivity in peatlands (Richard- son and Marshall, 1986; Walbridge, 1991). Despite the belief that peatlands are typically nutrient-poor, in situ rates of N mineralization in peatlands range from 0.8 to 7.7 g N m -2 yr -1 ; NITROGEN, PHOSPHORUS, AND CARBON MINERALIZATION IN RESPONSE TO NUTRIENT AND LIME ADDITIONS IN PEATLANDS Carmen T. Chapin 1 , Scott D. Bridgham 2 , John Pastor 3 , and Karen Updegraff 4 1 USDA/ARS Federal Nutrition Lab, Cornell University, Ithaca, NY 14853; Dr. Chapin is corresponding author. E-mail: ctc13@cornell.edu 2 Dept. of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556. 3 Natural Resources Research Institute and Dept. of Biology, University of Min- nesota-Duluth, Duluth, MN 55812. 4 Dept. of Forest Resources, University of Minnesota, St. Paul, MN 55108. Received Nov. 4, 2002; accepted Feb. 27, 2003. DOI: 10.1097/01.ss.0000075286.87447.5d This objective of this study was to determine if mineralization of C, N, and P was pH stressed and/or nutrient limited in a bog and fen in northeastern Minnesota. Although soil activity in northern peatlands can be limited by low pH, low temperatures, high C:N and C:P ratios of soil organic matter, and/or anaerobic conditions, different classes of peat- lands (bog and fen) vary in the type and degree of stress affecting soil processes. We employed in situ studies, laboratory incubations, and a fer- tilization and liming experiment to understand peatland mineralization dynamics further. Nitrogen mineralization in the field was higher in the fen than in the bog, but net P mineralization was close to zero in both sites. Soil cores were removed from plots that had been treated for 2 years with NH 4  , PO 4 2 , and/or CaCO 3 , followed by a 30-week lab in- cubation. Nutrient additions in the bog increased the labile N pool (N 0 ), and cumulative N and P mineralization over 30 weeks, but lime addition had no effect. Nutrient additions to the fen did not significantly alter nu- trient pool sizes (N 0 , P 0 ), cumulative mineralization totals, or mineral- ization rates. However, lime additions decreased potentially mineraliz- able N and cumulative N mineralization in the fen aerobic incubations, but increased cumulative P mineralization in the anaerobic incubations. Although both are peatlands, bog and fen nutrient cycles are controlled by different factors that may explain the differences in mineralization, to- tal soil N and P, and respective labile pools. This information may be es- pecially useful in anticipating changes brought about by anthropogenic nutrient/cation inputs and hydrologic alterations. (Soil Science 2003;168: 409–420) Key words: Mineralization, peatland, bog, fen, nitrogen, phosphorus, carbon.