Elevated CO sub(2) and temperature alter nitrogen allocation in Douglas-fir

The effects of elevated CO sub(2) and temperature on principal carbon constituents (PCC) and C and N allocation between needle, woody (stem and branches) and root tissue of Pseudotsuga menziesii Mirb. Franco seedlings were determined. The seedlings were grown in sun-lit controlled-environment chambers that contained a native soil. Chambers were controlled to reproduce ambient or ambient +180 ppm CO sub(2) and either ambient temperature or ambient +3.5 degree C for 4 years. There were no significant CO sub(2) x temperature interactions; consequently the data are presented for the CO sub(2) and temperature effects. At the final harvest, elevated CO sub(2) decreased the nonpolar fraction of the PCC and increased the polar fraction and amount of sugars in the needles. In contrast, elevated temperature increased the nonpolar fraction of the PCC and decreased sugars in needles. There were no CO sub(2) or temperature effects on the PCC fractions in the woody tissue or root tissue. Elevated CO sub(2) and temperature had no significant effects on the C content of any of the plant tissues or fractions. In contrast, the foliar N content declined under elevated CO sub(2) and increased under elevated temperature; there were no significant effects in other tissues. The changes in the foliar N concentrations were in the cellulose and lignin fractions, the fractions, which contain protein, and are the consequences of changes in N allocation under the treatments. These results indicate reallocation of N among plant organs to optimize C assimilation, which is mediated via changes in the selectivity of Rubisco and carbohydrate modulation of gene expression.