Biomass and CO2 flux in wet sedge tundras: responses to nutrients, temperature, and light

• Published in: Ecological monographs 1998-02, Vol.68 (1), p.75-97
• Main Authors: Shaver, G.R. (Ecosystem Studies Program, Arlington, VA.), Johnson, L.C, Cades, D.H, Murray, G, Laundre, J.A, Rastetter, E.B, Nadelhoffer, K.J, Giblin, A.E
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; arctic tundra; Biological and medical sciences; BIOMASA; BIOMASS; BIOMASSE; Biotic communities; CARBON DIOXIDE; CO2 flux; DIOXIDO DE CARBONO; DIOXYDE DE CARBONE; DISPONIBILIDAD DE NUTRIENTES; DISPONIBILITE D'ELEMENT NUTRITIF; ecosystem respiration; Environmental aspects; Fundamental and applied biological sciences. Psychology; gross ecosystem production; LIGHT; long-term manipulation; LUMIERE; LUZ; net ecosystem production; NUTRIENT AVAILABILITY; nutrients; photosynthesis; species composition; Synecology; TEMPERATURA; TEMPERATURE; Terrestrial ecosystems; TOUNDRA; TUNDRA; Tundra ecology; VEGETACION; VEGETATION
• ISSN: 0012-9615; 1557-7015
• DOI: 10.1890/0012-9615(1998)068[0075:BACFIW]2.0.CO;2

The aim of this research was to analyze the effects of increased N or P availability, increased air temperature, and decreased light intensity on wet sedge tundra in northern Alaska. Nutrient availability was increased for 6–9 growing seasons, using N and P fertilizers in factorial experiments at three separate field sites. Air temperature was increased for six growing seasons, using plastic greenhouses at two sites, both with and without N + P fertilizer. Light intensity (photosynthetically active photon flux) was reduced by 50% for six growing seasons at the same two sites, using optically neutral shade cloth. Responses of wet sedge tundra to these treatments were documented as changes in vegetation biomass, N mass, and P mass, changes in whole‐system CO2 fluxes, and changes in species composition and leaf‐level photosynthesis. Biomass, N mass, and P mass accumulation were all strongly P limited, and biomass and N mass accumulation also responded significantly to N addition with a small N × P interaction. Greenhouse warming alone had no significant effect on biomass, N mass, or P mass, although there was a consistent trend toward increased mass in the greenhouse treatments. There was a significant negative interaction between the greenhouse treatment and the N + P fertilizer treatment, i.e., the effect of the two treatments combined was to reduce biomass and N mass significantly below that of the fertilizer treatment only. Six years of shading had no significant effect on biomass, N mass, or P mass. Ecosystem CO2 fluxes included net ecosystem production (NEP; net CO2 flux), ecosystem respiration (RE, including both plant and soil respiration), and gross ecosystem production (GEP; gross ecosystem photosynthesis). All three fluxes responded to the fertilizer treatments in a pattern similar to the responses of biomass, N mass, and P mass, i.e., with a strong P response and a small, but significant, N response and N × P interaction. The greenhouse treatment also increased all three fluxes, but the greenhouse plus N + P treatment caused a significant decrease in NEP because RE increased more than GEP in this treatment. The shade treatment increased both GEP and RE, but had no effect on NEP. Most of the changes in CO2 fluxes per unit area of ground were due to changes in plant biomass, although there were additional, smaller treatment effects on CO2 fluxes per unit biomass, per unit N mass, and per unit P mass. The vegetation was composed mainly of rhizomatous