CO2 enrichment 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 their predicted effects on plant distribution and productivity. In this study we looked at the interaction between elevated CO2 and development of freezing tolerance in Norway spruce (Picea abies (L.) Karst.). First-year seedlings were grown under controlled conditions in an atmosphere enriched in CO2 (70 Pa) for one simulated growth season. We measured shoot growth, registered the timing of growth cessation and bud set, measured needle net photosynthetic rate, and determined needle carbohydrate concentration (fructose + pinitol, glucose, sucrose, inositol, raffinose and starch). Freezing tolerance (LT50) was determined after exposing whole seedlings to temperatures ranging from - 6.5 to - 36.0 degreesC and scoring for visual needle browning. Elevated CO2 did not affect height growth or the timing of growth cessation and bud set. The only statistically significant effects of CO2 treatment were on seedling dry weight, percent dry matter and starch content. During the three weeks after growth cessation and bud set, freezing tolerance increased from - 10 to - 35 degreesC, and there was a marked increase in all soluble sugars except inositol. However, neither freezing tolerance nor the concentration of soluble sugars was significantly influenced by elevated CO2.