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 elev ated CO2 environment. However, the variability and stability in growth responses among genotypes grown in a global change environment are ge nerally not documented. The present study investigated the differences , at the seedling stage, among 15 maternal families of jack pine (Pinu s banksiana Lamb.) in response to an elevated CO2-temperature environm ent (CO2T) (700 mu L CO2.L-1 with temperatures 4 degrees C higher than in the ambient CO2T environment), with different nitrogen concentrati ons. While the elevated CO2T did not significantly alter the overall h eight growth of seedlings, it significantly increased their total biom ass, 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 difference s were observed for height, biomass, and water-use efficiency. General ly, 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 s tability we observed in family response from the ambient to the elevat ed 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.