Changes in leaf nitrogen and carbohydrates underlie temperature and CO2 acclimation of dark respiration in five boreal tree species

We tested the hypothesis that acclimation of foliar dark respiration to CO2 concentration and temperature is associated with adjustments in leaf structure and chemistry. Populus tremuloides Michx, Betula papyrifera Marsh, Larix laricina (Du Roi) K, Koch, Pinus banksiana Lamb., and Picea mariana (Mill,) B.S.P. were grown from seed in combined CO2 (370 or 580 mu mol mol(-1)) and temperature treatments (18/12, 24/18, or 30/24 degrees C), Temperature and CO2 effects were predominately independent. Specific respiration rates partially acclimated to warmer thermal environments through downward adjustment in the intercept, but not Q(10) of the temperature-response functions. Temperature acclimation of respiration was larger for conifers than broad-leaved species and was associated with pronounced reductions in leaf nitrogen concentrations in conifers at higher growth temperatures. Shortterm increases in CO2 concentration did not inhibit respiration. Growth in the elevated CO2 concentration reduced leaf nitrogen and increased non-structural carbohydrate concentrations. However, for a given nitrogen concentration, respiration was higher in leaves grown in the elevated CO2 concentration, as rates increased with increasing carbohydrates, Across species and treatments, respiration rates were a function of both leaf nitrogen and carbohydrate concentrations (R-2 = 0.71, P < 0.0001). Longterm acclimation of foliar dark respiration to temperature and CO2 concentration is largely associated with changes in nitrogen and carbohydrate concentrations.