CO₂ enrichment and development of freezing tolerance in Norway spruce

Abstract

Plant growth and adaptation to cold and freezing temperatures in a CO 2 ‐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 CO 2 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 CO 2 (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 (LT 50 ) was determined after exposing whole seedlings to temperatures ranging from −6.5 to −36.0°C and scoring for visual needle browning. Elevated CO 2 did not affect height growth or the timing of growth cessation and bud set. The only statistically significant effects of CO 2 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°C, 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 CO 2 .