Short-term effects of fertilization on photosynthesis and leaf morphology of field-grown loblolly pine following long-term exposure to elevated CO2 concentration

This study examined the effects of an initial nitrogen (N) fertilizer application on the upper-canopy needle morphology and gas exchange of a loblolly pine tree exposed to elevated carbon dioxide (CO2) concentrations over a period of 9 years. Plots in the study were split, and one half of each plot was fertilized with 112 kg ha-1 of elemental N. Measurements included needle length, mass per unit area, N concentrations on a mass and area basis, light-saturated net photosynthesis per unit leaf area, and per unit mass and leaf conductance. Results of the study showed that fertilization had little impact on needle length, mass per unit area, or leaf conductance. Results suggested that although both needle age classes accumulated N following fertilization, current-year foliage incorporated N into its photosynthetic machinery, while 1-year old foliage stored N. No significant interactions were observed between elevated CO2 and light-saturated net photosynthesis per unit leaf area. The study found few fertilization and CO2 interaction effects on leaf physiology and morphology. 54 refs., 3 tabs., 3 figs