2002 ARCSS All-Hands Workshop

Long-term Responses of Wet Sedge Tundra to Changes in Nutrients, Temperature, and Light

Heather M. Rueth¹, Gaius R. Shaver², Martin Sommerkorn³, Knute J. Nadelhoffer^4
1The Ecosystems Center , Marine Biological Laboratory, 7 Water Street, Woods Hole , MA, 02543, USA, Phone 508 289 7727, Fax 508 457 1548, hrueth@mbl.edu
²The Ecosystems Center , Marine Biological Laboratory, 7 Water Street, Woods Hole, MA, 02543, USA, Phone 508 2897492, Fax 508 457 1548, gshaver@mbl.edu
³The Ecosystems Center , Marine Biological Laboratory, 7 Water Street, Woods Hole, MA, 02543, USA, Phone 508 289 7583, Fax 508 457 1548, msommerkorn@mbl.edu
⁴The Ecosystems Center , Marine Biological Laboratory, 7 Water Street, Woods Hole, MA, 05243, USA, Phone 508 289 7493, Fax 508 457 1548, knute@mbl.edu

We examined the long-term responses of wet sedge tundra to changes in nutrient availability, temperature and light. Measurements of biomass, species composition, ecosystem CO₂ flux and plant N pools were conducted in 1994 after 6-9 years of treatment and in 2001 after 13-16 years of treatment, allowing a comparison of the short-term vs. longer-term vegetative responses to treatment. Unlike tussock tundra, after 13-16 years of treatment wet sedge biomass has leveled-off or declined in fertilized plots, while species composition continues to change. Changes in species composition appear to have a limited impact on aboveground N concentrations, biomass N, and ecosystem CO₂ flux. Ecosystem CO₂ flux was greater in 2001 than 1994 despite lower biomass in 2001. CO₂ flux per-unit-biomass and per-unit-biomass N were also greater in 2001 than 1994. Graminoid blade %N was consistently greater in 2001 compared to 1994, which could explain the higher CO₂ flux rates in 2001. Fertilization increased belowground biomass and decreased the ratio of below- to aboveground biomass.

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