Effects of CO2 enrichment, elevated temperature, and nitrogen availability on the growth and gas exchange of different families of jack pine seedlings

Many economically important tree species respond positively to an elevated CO2 environment. However, the variability and stability in growth responses among genotypes grown in a global change environment are generally not documented. The present study investigated the differences, at the seedling stage, among 15 maternal families of jack pine (Pinus banksiana Lamb.) in response to an elevated CO2-temperature environment (CO2T) (700 mu L CO2.L-1 with temperatures 4 degrees C higher than in the ambient CO2T environment), with different nitrogen concentrations. While the elevated CO2T did not significantly alter the overall height growth of seedlings, it significantly increased their total biomass, with needle and root biomass being most responsive. Growth in the elevated CO2T resulted in a 24% reduction in the leaf weight ratio as more biomass was allocated to roots. Significant genotypic differences were observed for height, biomass, and water-use efficiency. Generally, most families kept their rank relative to other families, from the ambient to the elevated CO2T. Also, rank correlations between height of families grown in elevated CO2T and height of families at 10 years of age in the field were significant. This result, combined with the stability we observed in family response from the ambient to the elevated CO2T, suggested that jack pine families currently chosen for their fast-growing capacity will probably remain as such in a global change environment, at least during the seedling establishment stage.