Responses of growth, nitrogen and carbon partitioning to elevated atmospheric CO2 concentration in live oak (Quercus virginiana Mill.) seedlings in relation to nutrient supply

Live oak (Quercus virginiana Mill.) seedlings were exposed at two concentra tions of atmospheric carbon dioxide ([CO2], 370 or 520 mu mol.mol(-1)) in c ombination with two soil nitrogen (N) treatments (20 and 90 mu mol.mol(-1) total N) in open-top chambers for 6 months. Seedlings were harvested at 5-7 weeks interval. CO2 treatment had a positive effect on seedling growth. Di fferences in biomass between elevated and ambient CO2-treated plants increa sed over the experimental period. Soil N availability did not significantly affect growth. Nevertheless, growth in elevated [CO2] in combination with high N levels led to a consistently higher accumulation of total biomass by the end of the experiment (30-40 %). Biomass allocation between plant part s was similar for seedlings in all treatments, but was significantly differ ent between harvests. The N regimes did not result in different relative gr owth rate (RGR) and net assimilation rate (NAR), while CO2 treatment had an overall significant effect. Across all [CO2] and N levels, there was a pos itive relationship between plant mass and subsequent RGR, and this relation ship did not differ between treatments. Overall, specific leaf area (SLA) d l:creased in CO2-enriched air. Fine root-foliage mass ratio was increased b y elevated [CO2] and decreased by high N. High CO2- and high N-treated plan ts had the greatest height and basal stem diameter. The allometric relation ships between shoot and root dry weight and between height and basal stem d iameter were not significantly affected by elevated [CO2]. Leaf N concentra tions were reduced by low soil N. Plant N concentrations decreased with tim e. Elevated [CO2] increased the C/N ratio of all plant compartments, as a r esult of decreasing N concentrations. High CO2-grown plants reduced N conce ntrations relative to ambient CO2-grown plants when compared at a common ti me, but similar when compared at a common size. ((C) Inra/Elsevier, Paris.) .