SOIL-GAS FLUXES OF N2O, CH4 AND CO2 BENEATH LOLIUM-PERENNE UNDER ELEVATED CO2 - THE SWISS FREE-AIR CARBON-DIOXIDE ENRICHMENT EXPERIMENT

Fluxes of nitrous oxide, methane and carbon dioxide were measured from soils under ambient (350 mu L L-1) and enhanced (600 mu L L-1) carbon dioxide partial pressures (pCO(2)) at the 'Free Air Carbon Dioxide En richment' (FACE) experiment, Eidgenossische Technische Hochschule (ETH ), Eschikon, Switzerland in July 1995, using a GC housed in a mobile l aboratory. Measurements were made in plots of Lolium perenne maintaine d under high N input. During the data collection period N fertiliser w as applied at a rate of 14 g m(-2) of N. Elevated pCO(2) appeared to r esult in an increased (27%) output of N2O, thought to be the consequen ce of enhanced root-derived available soil C, acting as an energy sour ce for denitrification. The climate, agricultural practices and soils at the FACE experiment combined to give rise to some of the largest N2 O emissions recorded for any terrestrial ecosystem. The amount of CO2- C being lost from the control plot was higher (10%) than for the enhan ced CO2 plot, and is the reverse of that predicted. The control plot o xidised consistently more CH4 than the enhanced plot, oxidising 25.5 /- 0.8 mu g m(-2) hr(-1) of CH4 for the control plot, with an average of 8.5 +/- 0.4 mu g m(-2) hr(-1) of CH4 for the enhanced CO2 plot. Thi s suggests that elevated pCO(2) may lead to a feedback whereby less CH 4 is removed from the atmosphere. Despite the limited nature of the cu rrent study (in time and space), the observations made here on the int eractions of elevated pCO(2) and soil trace gas release suggest that s ignificant interactions are occurring. The feedbacks involved could ha ve importance at the global scale.