CO2 enrichment, nitrogen fertilization and development of freezing tolerance in Norway spruce

Plant growth and adaptation to cold and freezing temperatures in a CO2-enriched atmosphere have received little attention despite the predicted effects of elevated CO2 on plant distribution and productivity. Norway spruce [Picea abies (L.) Karst.] seedlings from latitudinally distinct seed sources (66degreesN and 60degreesN) were grown for one simulated growth season under controlled conditions in an atmosphere enriched in CO2 (70 Pa) and at ambient CO2 (40 Pa), combined factorially with low (3.6 mM) or high (15.7 mM) concentrations of nitrogen fertilization. There was a clear difference between the two provenances in height growth, in the timing of bud set, and in freezing tolerance. Nitrogen fertilization increased height growth in both provenances, while CO2 enrichment stimulated height growth only in the southern provenance. We found no significant effects of elevated CO2 or nitrogen fertilization on the timing of bud set. During cold acclimation, freezing tolerance increased from -10degreesC to -35degreesC, and there was a marked increase in all soluble sugars except inositol. Elevated CO2 in combination with high nitrogen led to a slight increased freezing tolerance in both provenances during the early stages of cold acclimation. However, towards the end of cold acclimation, elevated CO2 and high nitrogen led to reduced freezing tolerance in the southern provenance, while elevated CO2 and low nitrogen reduced freezing tolerance in the northern provenance. These results suggest that CO2 enrichment influences the development of freezing tolerance, and that these responses differ with available nitrogen and between provenances.