Effects of elevated CO2 level and N and P supplies on two winter wheat varieties in the early developmental stage

Two winter wheat varieties were grown in growth chambers under controlled e nvironmental conditions at two atmospheric CO2 concentrations (375 and 750 ppm) and different soil nitrogen and phosphorus levels. Data on plant heigh t, tiller number, leaf number, leaf area, shoot and root dry weight were re corded in the 6(th) week after planting. The plants responded positively to CO2 enhancement for most of the parameters examined, producing more root a nd aboveground biomass. Low soil nitrogen concentrations decreased the infl uence of CO2 enrichment, while nitrogen at above-optimum levels tended to s uppress growth. High CO2 concentration, however, had stimulating effects at inhibiting nitrogen doses. There was a shift in optimum soil N for the sho ot dry weight due to the doubling of atmospheric CO2. In this young develop mental stage the effect of phosphorus was not as pronounced as that of nitr ogen, though P interacted with N at the highest N concentration where a pos itive relationship was found which moderated the inhibiting effects.