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

Abstract

We determined the direct effects of atmospheric CO2 concentration ([CO2]) on leaf gas exchange, phenolic and carbohydrate allocation in live oak seedlings (Quercus virginiana Mill.) grown at present (370 μmol · mol-1) or elevated (520 μmol · mol-1) [CO2] for 6 months in open-top chambers. Two soil nitrogen (N) treatments (20 and 90 μmol · mol-1 total N, low N and high N treatments, respectively) were imposed by watering the plants every 5 d with modified water soluble fertilizer. Enhanced rates of leaf-level photosynthesis were maintained in plants subjected to elevated [CO2] over the 6-month treatment period in both N treatments. A combination of increased rates of photosynthesis and decreased stomatal conductance was responsible for nearly doubling water use efficiency under elevated [CO2]. The sustained increase in photosynthetic rate was accompanied by decreased dark respiration in elevated [CO2]. Elevated [CO2] led to increased growth rates, while total non-structural carbohydrate (sugars and starch) concentrations were not significantly affected by elevated [CO2] treatment. The concentration of phenolic compounds increased significantly under elevated [CO2].