The effect of elevated atmospheric CO2 concentration and nutrient supply on gas exchange, carbohydrates and foliar phenolic concentration in live oak(Quercus virginiana Mill.) seedlings

We determined the direct effects of atmospheric CO2 concentration ([CO2]) o n leaf gas exchange, phenolic and carbohydrate allocation in live oak seedl ings (Quercus virginiana Mill.) grown at present (370 mu mol.mol(-1)) or el evated (520 mu mol.mol(-1)) [CO2] for 6 months in open-top chambers. Two so il nitrogen (N) treatments (20 and 90 mu mol.mol(-1) total N, low N and hig h N treatments, respectively) were imposed by watering the plants every 5 d with modified water soluble fertilizer. Enhanced rates of leaf-level photo synthesis were maintained in plants subjected to elevated [CO2] over the 6- month treatment period in both N treatments. A combination of increased rat es of photosynthesis and decreased stomatal conductance was responsible for nearly doubling water use efficiency under elevated [CO2]. The sustained i ncrease in photosynthetic rate was accompanied by decreased dark respiratio n in elevated [CO2]. Elevated [CO2] led to increased growth rates; while to tal non-structural carbohydrate (sugars and starch) concentrations were not significantly Affected by elevated [CO2] treatment. The concentration of p henolic compounds increased significantly under elevated [CO2]. ((C) Inra/E lsevier, Paris.).