|Peter M. Groffman
Institute of Ecosystem Studies
Millbrook, NY 12545 USA
phone: (845) 677-7600 ext 128
fax: (845) 677-5976
WE ARE MONITORING a suite of variables associated with soil carbon (C) and nitrogen (N) cycling in Watershed 1 (treated) and west of Watershed 6 (reference). This suite of variables includes microbial biomass C, N and P content, potential net N mineralization and nitrification, readily available/respirable C and KCl extractable inorganic N. Microbial biomass C and N content are indices of the capacity of an ecosystem to support nutrient cycling functions (Smith and Paul, 1990). We measured denitrification enzyme activity as an index of the denitrification capacity of different sites. This activity has been found to be strongly related to annual denitrification rate in soils (Groffman and Tiedje, 1989). Additional variables measured included potential net N mineralization and nitrification, and soil respiration. The supply of N through mineralization is an important component of soil fertility and potential net nitrification is often used as an indicator of high N availability in ecosystems. Ecosystems (including wetlands) with high net nitrification are thought to be susceptible to high N losses if disturbed by harvest, fire, blowdowns or other perturbations (Vitousek et al., 1982; Pastor et al., 1984; Aber et al., 1989). Soil respiration is a useful index of overall soil biological activity (Paul and Clark, 1996) and is a critical component of ecosystem C storage.
We have analyzed (and posted the datasets area) all data collected through fall of 2001. We are beginning to see indications of changes in N and C cycling including:
- An increase in nitrate and readily available/respirable C in the mineral soil (Figure 1). It is likely that these have leached into the mineral soil from the Oie and Oa horizons above, as a result of the marked increases in soil pH these horizons have experienced in response to the Ca addition.
- Increased nitrification rates in the Oie horizon (Figure 2). Nitrification is considered to be a pH sensitive process. The increases we have observed are likely linked to marked increases in soil pH in the Oie horizon in response to the Ca addition (Figure 3).
|Figure 1.Soil nitrate (top) and respiration (bottom) in the mineral soil of calcium treated and reference watersheds at four elevations from 1998 - 2001. Calcium was applied after sampling in 1999. Note that levels of nitrate and respiration appear to be increased in the treated watershed in 2001.|
|Figure 2. Potential net nitrification in the Oie horizon of calcium treated and reference watersheds at four elevations from 1998 - 2001. Calcium was applied after sampling in 1999. Note that levels of nitrification appear to be increased in the treated watershed in 2001.|
|Figure 3. Soil pH in the forest floor (Oie and Oa) horizons of calcium treated and reference watersheds at four elevations in October 2000. Calcium was applied in October 1999.
Aber, J.D., K.J. Nadelhoffer, P. Steudler, and J.M. Melillo. 1989. Nitrogen saturation in northern forest ecosystems. BioScience 39:378-386.
Groffman, P.M., and J.M. Tiedje. 1989. Denitrification in north temperate forest soils: Relationships between denitrification and environmental factors at the landscape scale. Soil Biology & Biochemistry 21:621-626.
Pastor, J., J.B. Aber, C.A. McClaugherty, and J.M. Melillo. 1984. Aboveground production and N and P cycling along a nitrogen mineralization gradient on Blackhawk Island, Wisconsin. Ecology 65:256-268.
Paul, E.A., and F.E. Clark. 1996. Soil Microbiology and Biochemistry, 2nd Edition. Academic Press, New York.
Smith, J.S., and E.A. Paul. 1990. The significance of soil microbial biomass estimations. p. 357-369 In J.M. Bollag and G. Stotzky (eds.) Soil Biochemistry, Volume 6. Marcel Dekker, Inc. New York.
Vitousek, P.M., J.R. Gosz, C.C. Grier, J.M. Melillo, W.A. Reiners, and R.L. Todd. 1982. A comparative analysis of potential nitrification and nitrate mobility in forest ecosystems. Ecological Monographs 52:155-177.
Date Prepared: November 2002