Potassium Limits Potential Growth Of Bog Vegetation Under Elevated Atmospheric Co2 And N Deposition

Abstract

The free air carbon dioxide enrichment (FACE) and Nￂﾠdeposition experiments on four ombrotrophic bogs in Finland, Sweden, the Netherlands and Switzerland, revealed that after three years of treatment: (1) elevated atmospheric CO2concentration had no significant effect on the biomass growth ofSphagnumand vascular species; and (2) increased Nￂﾠdeposition reduced Sphagnum growth, because it increased the cover of vascular plants and the tall mossPolytrichum strictum, while vascular plant biomass growth was not affected. This paper focuses on water chemistry, plant nutrient content, and litter decomposition rates. Potassium limitation, or low supply of Kￂﾠand P, may have prevented a significant increase ofSphagnumgrowth under elevated CO2and Nￂﾠdeposition. Vascular plant growth under elevated CO2and Nￂﾠdeposition was also limited by K, or by Kￂﾠin combination with Pￂﾠor Nￂﾠ(N in CO2experiment). Elevated CO2and Nￂﾠdeposition had no effect on decomposition rates ofSphagnumand vascular plant litter. Aside from a possible effect of Nￂﾠdeposition on light competition between species, we expect that elevated atmospheric CO2and Nￂﾠdeposition concentrations will not affectSphagnumand vascular plant growth in bogs of north￢ﾀﾐwest Europe due to K￢ﾀﾐ, or Kￂﾠin combination with N￢ﾀﾐ or P￢ﾀﾐ, limited growth. For the same reason we expect no effect of elevated CO2and Nￂﾠdeposition on litter decomposition. Net primary production of raised ombrotrophic bogs that are at or close to steady state, is regulated by input of nutrients through atmospheric deposition. Therefore, we hypothesize that the expected increase of plant growth under elevated CO2and Nￂﾠdeposition is diminished by current levels of Kￂﾠ(and to some extent Pￂﾠand N) in atmospheric deposition.