EFFECTS OF ELEVATED CARBON-DIOXIDE ON 3 GRASS SPECIES FROM MONTANE PASTURE .2. NUTRIENT-UPTAKE, ALLOCATION AND EFFICIENCY OF USE

Agrostis capillaris L.(4), Festuca vivipara L. and Poa alpina L. were grown in outdoor open-top chambers at either ambient (340 mu mol mol(-1) or elevated (680 mu mol mol(-1)) CO2 for periods from 79 to 189 d. Under these conditions there is increased growth of A, capillaris and P. alpina, but reduced growth of F. vivipara. Nutrient use efficiency, nutrient productivity (total plant dry weight gain per unit of nutrient) and nutrient allocation of all three grass species were measured in an attempt to understand their individual growth responses further and to determine whether altered nutrient-use efficiencies and productivities enable plants exposed to an elevated atmospheric CO2 environment to overcome potential limitations to growth imposed by soil fertility. Total uptake of nutrients was, in general, greater in plants of A. capillaris and P. alpina (with the exception of N and K in the latter) when grown at 680 mu mol mol(-1) CO2. In F. vivipara, however, uptake was considerably reduced in plants grown at the higher CO2 concentration. Overall, a doubling of atmospheric CO2 concentration had little effect on the nutrient use efficiency or productivity of A, capillaris. Reductions in tissue nutrient content resulted from increased plant growth and not altered nutrient use efficiency. In P. alpina, potassium, magnesium and calcium productivities were significantly reduced and photosynthetic nitrogen and phosphorus use efficiencies were doubled at elevated CO2 with respect to plants grown at ambient CO2. F. vivipara grown for 189 d showed the most marked changes in nutrient use efficiency and nutrient productivity (on an extracted dry weight basis) when grown at elevated CO2. F. vivipara grown at elevated CO2, however, showed large increases in the ratio of nonstructural carbohydrate to nitrogen content of leaves and reproductive tissues, indicating a substantial imbalance between the production and utilization of assimilate.