GROWTH-RESPONSES OF 2 CONTRASTING UPLAND GRASS SPECIES TO ELEVATED CO2 AND NITROGEN CONCENTRATION

Growth parameters of Agrostis capillaris L. and Nardus stricta L. were measured in relation to ambient and elevated concentrations of CO2 (3 40 and 550 mul CO2 l-1, respectively) and at low and high concentratio ns of nitrogen (0.8 and 3 mm NH4NO3, respectively). After 60 d of grow th A. capillaris had attained approx. four times the total dry weight of N. stricta in all treatments, which was attributed to the greater l eaf area ratio of the former. A. capillaris grown at the low nitrogen concentration attained 30% of the total dry weight of plants grown at high nitrogen. Over the 60 d period, destructive harvests (seven in to tal) showed the growth of N. stricta to be less sensitive than that of A. capillaris to the concentration of nitrogen, but in both species g rowth analysis showed the lower total dry weight at low nitrogen to be attributable to lower unit leaf rate. There was a differential respon se of both species to elevated concentrations of CO2 which was nitroge n dependent. A. capillaris grown at elevated CO2 attained a greater to tal dry weight than at ambient CO2 and this response was proportionate ly greater at low nitrogen (78% increase) than at high nitrogen (58% i ncrease). In contrast, in N. stricta there was no effect of CO2 concen tration on the total dry weight at low nitrogen whilst at high nitroge n plants grown at elevated CO2 had a greater total dry weight after 48 d of growth. Calculation of the allometric coefficient (K) relating r oot growth to shoot growth indicated that the effect of the lower nitr ogen concentration was to increase partitioning to the roots while the higher CO2 concentration did not alter partitioning.