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.) n eedles exposed to either ambient CO2 concentration ([CO2]), ambient plus 17 5 or ambient plus 350 mu mol CO2 mol(-1) in branch chambers for 2 years. Th e CO2 treatments were superimposed on a 2 x 2 factorial combination of irri gation and fertilization treatments. In addition, we compared the effects o f branch chambers and open-top chambers on needle chemistry. Pro-anthocyani din and N concentrations were measured in needles from branch chambers and from trees in open-top chambers exposed concurrently for two years to eithe r ambient [CO2] or ambient plus 200 mu mol Co-2 mol(-1) in combination with a fertilization treatment. In the branch chambers, concentrations of total soluble phenolics in needles generally increased with needle age. Concentr ations of total soluble phenolics, catechin and PA in needle extracts incre ased about 11% in response to the elevated [CO2] treatments. There were no significant treatment effects on foliar lignin concentrations. Nitrogen con centrations were about 10% lower in needles from the elevated [CO2] treatme nts 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 statisti cally significant. Needle N concentrations increased 23% in response to fer tilization. Treatment effects on PA and N concentrations were similar betwe en branch and open-top chambers, although in this part of the study N conce ntrations were not significantly affected by the CO2 treatments in either t he branch or open-top chambers. We conclude that elevated [CO2] and low N a vailability affected foliar chemical composition, which could in turn affec t plant-pathogen interactions, decomposition rates and mineral nutrient cyc ling.