Effects of elevated CO2 and vascular plants on evapotranspiration in bog vegetation

We determined evapotranspiration in three experiments designed to study the effects of elevated CO2 and increased N deposition on ombrotrophic bog vegetation. Two experiments used peat monoliths with intact bog vegetation in containers, with one experiment outdoors and the other in a greenhouse. A third experiment involved monocultures and mixtures of Sphagnum magellanicum and Eriophorum angustifolium in containers in the same greenhouse. To determine water use of the bog vegetation in JulyAugust for each experiment and each year we measured water inputs and outputs from the containers. We studied the effects of elevated CO2 and N supply on evapotranspiration in relation to vascular plant biomass and exposure of the moss surface (measured as height of the moss surface relative to the container edge). Elevated CO2 reduced water use of the bog vegetation in all three experiments, but the CO2 effect on evapotranspiration interacted with vascular plant biomass and exposure of the moss surface. Evapotranspiration in the outdoor experiment was largely determined by evaporation from the Sphagnum moss surface (as affected by exposure to wind) and less so by vascular plant transpiration. Nevertheless, elevated CO2 significantly reduced evapotranspiration by 910␒n the outdoor experiment. Vascular plants reduced evapotranspiration in the outdoor experiment, but increased water use in the greenhouse experiments. The relation between vascular plant abundance and evapotranspiration appears to depend on wind conditions; suggesting that vascular plants reduce water losses mainly by reducing wind speed at the moss surface. Sphagnum growth is very sensitive to changes in water level; low water availability can have deleterious effects. As a consequence, reduced evapotranspiration in summer, whether caused by elevated CO2 or by small increases in vascular plant cover, is expected to favour Sphagnum growth in ombrotrophic bog vegetation.

[1]  F. Miglietta,et al.  Spatial and Temporal Performance of the MiniFACE (Free Air CO2 Enrichment) System on Bog Ecosystems in Northern and Central Europe , 2001, Environmental monitoring and assessment.

[2]  R. S. Clymo,et al.  The Ecology of Sphagnum , 1982 .

[3]  H. Rydin,et al.  Response of photosynthesis of Sphagnum species from contrasting microhabitats to tissue water content and repeated desiccation. , 1998, The New phytologist.

[4]  C. Field,et al.  CO2 effects on the water budget of grassland microcosm communities , 1997 .

[5]  A. Knapp,et al.  Biomass production and species composition change in a tallgrass prairie ecosystem after long‐term exposure to elevated atmospheric CO2 , 1999 .

[6]  F. Miglietta,et al.  Elevated CO2 concentrations and stomatal density: observations from 17 plant species growing in a CO2 spring in central Italy , 1998 .

[7]  E. Schulze,et al.  Relationships among Maximum Stomatal Conductance, Ecosystem Surface Conductance, Carbon Assimilation Rate, and Plant Nitrogen Nutrition: A Global Ecology Scaling Exercise , 1994 .

[8]  Christopher B. Field,et al.  Stomatal responses to increased CO2: implications from the plant to the global scale , 1995 .

[9]  B. Drake,et al.  12 – Long-Term Elevated CO2 Exposure in a Chesapeake Bay Wetland: Ecosystem Gas Exchange, Primary Production, and Tissue Nitrogen , 1996 .

[10]  F. Berendse,et al.  Interactions between elevated CO2 concentration, nitrogen and water: effects on growth and water use of six perennial plant species , 1998 .

[11]  A. Knapp,et al.  Water vapour fluxes and their impact under elevated CO2 in a C4‐tallgrass prairie , 1997 .

[12]  F. Berendse,et al.  Effects of elevated carbon dioxide and increased nitrogen deposition on bog vegetation in the Netherlands , 2001 .

[13]  R. S. Clymo,et al.  Profiles of water content and pore size in Sphagnum and peat, and their relation to peat bog ecology , 1982, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[14]  E. Gorham.  Northern Peatlands: Role in the Carbon Cycle and Probable Responses to Climatic Warming. , 1991, Ecological applications : a publication of the Ecological Society of America.