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

Abstract

Live oak (Quercus virginiana Mill. seedlings were exposed at two concentrations of atmospheric carbon dioxide ([CO2], 370 or 520 μmol · mol-1) in combination with two soil nitrogen (N) treatments (20 and 90 μmol · 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. Differences in biomass between elevated and ambient CO2-treated plants increased 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 parts was similar for seedlings in all treatments, but was significantly different between harvests. The N regimes did not result in different relative growth rate (RGR) and net assimilation rate (NAR), while CO2 treatment had an overall significant effect. Across all [CO2] and N levels, there was a positive relationship between plant mass and subsequent RGR, and this relationship did not differ between treatments. Overall, specific leaf area (SLA) decreased in CO2-enriched air. Fine root-foliage mass ratio was increased by elevated [CO2] and decreased by high N. High CO2- and high N-treated plants had the greatest height and basal stem diameter. The allometric relationships between shoot and root dry weight and between height and basal stem diameter were not significantly affected by elevated [CO2]. Leaf N concentrations were reduced by low soil N. Plant N concentrations decreased with time. Elevated [CO2] increased the C/N ratio of all plant compartments, as a result of decreasing N concentrations. High CO2-grown plants reduced N concentrations relative to ambient CO2-grown plants when compared at a common time, but similar when compared at a common size.