Elevated CO2 and N: effects on growth and photosynthesis of Dactylis Glomerata L.[abstract]

Growth responses of Dactylis glomerata L. at elevated [C02 ] (680 µmo! mo1• were analysed in controlled environments at two concentrations of nitrogen (1.5 and 6.0 m M N03-). The dry weight of plants grown at elevated [C02] was significantly increased at both levels of N-supply due to a transient increase in the relative growth rate during early stages of growth. The instantaneous decrease in leaf area ratio (LAR) and specific leaf area (SLA) of plants grown at elevated [C02] was not observed when growth was analysed allometrically. This suggests that the observed instantaneous decrease in L AR and SLA is due to the increase in dry weight of plants at elevated [CO2]. In order to test whether growth at elevated [CO,] results i n a reduction of the photosynthetic capacity (acclimation), the light-saturated response of the net CO, uptake (A) to intercellular C02 concentration (Ci) was determined for leaf 5, two days after full expansion. The in vivo maximum rate of carboxylation (V,,m,J and the CO,-saturated rate of photosynthesis (Am,J were significantly decreased in plants grown at elevated [C02] and low nitrogen (0.15 and 1.6mM (N03-). No effect of elevated [CO,] on V,;m°' and Arna, was observed when plants were grown at high nitrogen (1.5 and 6.0 mM >J03-). The observed acclimation at limited nitrogen supply may be due to the fact that plants grown at elevated [C02 J are bigger and therefore experience a more severe nitrogen deficiency.