Competition betweenSphagnum magellanicumandEriophorum angustifoliumas affected by raised CO2and increased N deposition

Abstract

The competition between peat mosses (Sphagnum) and vascular plants as affected by raised CO2and increased N deposition was studied in a glasshouse experiment by exposing peat monoliths with monocultures and mixtures ofSphagnummagellanicumandEriophorumangustifoliumto ambient (350 ppmv) or raised (560 ppmv) atmospheric CO2concentrations, combined with low (no N addition) or high (5 g m−2yr−1added) N deposition. Growth of the two species was monitored for three growing seasons. The presence ofEriophorumdid not affectSphagnumbiomass, becauseEriophorumdensity did not become high enough to severely shade the moss surface. In contrast,Sphagnumhad a negative effect onEriophorumbiomass, particularly on the number of flowering stems. Possibly, the presence of a livingSphagnumlayer decreased nutrient availability toEriophorumby immobilising nutrients mineralised from the peat. Raised CO2and/or increased N deposition did not change these competitive relationships betweenSphagnumandEriophorum, but had independent effects. Raised CO2had a positive effect both onSphagnumandEriophorumbiomass, though onEriophorumthe effect was transient, probably because of P limitation. Nitrogen addition had a direct negative effect onSphagnumheight growth in the first growing season, but by the third year an increased shoot density had cancelled this out, so no N effect onSphagnumbiomass was present at the end of the experiment. The response ofEriophorumto N addition was small; N availability appeared not to limit its growth.