EFFECTS OF ELEVATED CO2, NITROGEN FORM AND CONCENTRATION ON GROWTH AND PHOTOSYNTHESIS OF A FAST-GROWING AND SLOW-GROWING GRASS

Growth and photosynthesis of Agrostis capillaris L. and Nardus stricta L. were measured for plants grown under ambient and elevated concentr ations of CO2 (340 and 550 mu l CO2 l(-1) respectively) and a range of nitrogen concentrations (0.01, 0.1, 1 and 5 mg N l(-1)) supplied as e ither ammonium sulphate or sodium nitrate. After 42 d of growth for A. capillaris and 49 d of growth for N. stricta, the higher nitrogen con centrations resulted in stimulation of growth. The form of nitrogen di d not affect the total dry weight attained by A. capillaris. However, ammonium-grown N. stricta attained a greater total dry weight than did nitrate-grown plants. Nitrogen form influenced leaf area ratio, which was greater in nitrate-grown A. capillaris and in ammonium-grown N. s tricta. At the two lowest nitrogen concentrations there was no effect of elevated CO2 on total dry weight in either species, whilst at the t wo highest nitrogen concentrations positive growth responses to elevat ed CO2 were observed. Photosynthetic capacity and carboxylation effici ency were lower in plants grown in elevated CO2 at the two lowest nitr ogen concentrations, and were associated with greater leaf soluble car bohydrate content and lower foliar nitrogen concentrations. By contras t, the CO2 treatment did not affect these parameters at the two highes t nitrogen concentrations employed.