GROWTH AND REGROWTH OF PHLEUM-PRATENSE, LOLIUM-PERENNE, TRIFOLIUM-REPENS AND TRIFOLIUM-PRATENSE AT NORMAL AND ELEVATED CO2 CONCENTRATION

The effect of elevated CO2 concentration (680 +/- 52 mu mol mol(-1)) o n growth of three cultivars of Phleum pratense, two of Lolium perenne and one of Trifolium repens and Trifolium pratense each, was studied d uring one growth season including three harvests. The study was perfor med in ten 9 m(2) field chamber units in a cool maritime climate under long days (15-18 h), on the southwest coast of Norway (59 degrees N, 6 degrees E). Tillering in P. pratense and L. perenne was not signific antly affected in the first harvest (June/July), but was increased by 30% in the third harvest (September) in response to elevated CO2 conce ntrations. The plant height was reduced by 16-24% in P. pratense and b y 25-29% in L. perenne at high CO2. The dry weight yield of the two gr ass species was negatively affected by elevated CO2 in the two first h arvests, however, no effect was found in the last harvest. The total h arvestable dry matter was decreased by 18% in P. pratense and 13% in L . perenne. The dry matter of the stubble was increased at elevated CO2 , by 18% in P. pratense and 26% in L. perenne, leaving more of the yie ld in the meadow after harvest. Raising the CO2 concentration increase d the dry weight by 30% in both clover species. The results are discus sed in relation to the climatic conditions during the season.