Atmospheric carbon dioxide, irrigation, and fertilization effects on phenolic and nitrogen concentrations in loblolly pine (Pinus taeda) needles
Concentrations of total soluble phenolics, catechin, proanthocyanidins (PA), lignin and nitrogen (N) were measured in loblolly pine (Pinus taeda L.) needles exposed to either ambient CO2 concentration ([CO2]), ambient plus 175 or ambient plus 350 µmol O2 mol-1 in branch chambers for 2 years. The CO2 treatments were superimposed on a 2 × 2 factorial combination of irrigation and fertilization treatments. In addition, we compared the effects of branch chambers and open-top chambers on needle chemistry. Pro-anthocyanidin and N concentrations were measured in needles from branch chambers and from trees in open-top chambers exposed concurrently for two years to either ambient [CO2]or ambient plus 200 µmol CO2 mol-1 in combination with a fertilization treatment. In the branch chambers, concentrations of total soluble phenolics in needles generally increased with needle age. Concentrations of total soluble phenolics, catechin and PA in needle extracts increased about 11% in response to the elevated [CO2] treatments. There were no significant treatment effects on foliar lignin concentrations. Nitrogen concentrations were about 10% lower in needles from the elevated [CO2] treatments than in needles from the ambient [CO2] treatments. Soluble phenolic and PA concentrations were higher in the control and irrigated soil treatments in about half of the comparisons; otherwise, differences were not statistically significant. Needle N concentrations increased 23% in response to fertilization. Treatment effects on PA and Nconcentrations were similar between branch and open-top chambers, although in this part of the study N concentrations were not significantly affected by the CO2 treatments in either the branch or open-top chambers. We conclude that elevated [CO2] and low N availability affecte foliar chemical composition, which could in turn affect plant pathogen in teractions, decomposition rates and mineral nutrient cycling.