EFFECTS OF ELEVATED CO2 CONCENTRATION ON PHOTOSYNTHESIS, RESPIRATION AND CARBOHYDRATE STATUS OF COPPICE POPULUS HYBRIDS

To determine how increased atmospheric CO2 will affect the physiology of coppiced plants, sprouts originating from two hybrid poplar clones (Populus trichocarpa x P. deltoides - Beaupre and P. deltoides x P. ni gra - Robusta) were grown in open-top chambers containing ambient or e levated (ambient + 360 mu mol mol(-1)) CO2 concentration. The effects of elevated CO2 concentration on leaf photosynthesis, stomatal conduct ance, dark respiration, carbohydrate concentration and nitrogen concen tration were measured. Furthermore, dark respiration of leaves was par titioned into growth and maintenance components by regressing specific respiration rate vs specific growth rate. Sprouts of both clones expo sed to CO2 enrichment showed no indication of photosynthetic down-regu lation. During reciprocal gas exchange measurements, CO2 enrichment si gnificantly increased photosynthesis of all sprouts by approximately 6 0% (P < 0.01) on both an early and late season sampling date, decrease d stomatal conductance of all sprouts by 10% (P < 0.04) on the early s ampling date and nonsignificantly decreased dark respiration by an ave rage of 11%. Growth under elevated CO2 had no consistent effect on fol iar sugar concentration but significantly increased foliar starch by 8 0%. Respiration rate was highly correlated with both specific growth r ate and percent nitrogen. Long-term CO2 enrichment did not significant ly affect the maintenance respiration coefficient or the growth respir ation coefficient. Carbon dioxide enrichment affected the physiology o f the sprouts the same way it affected these plants before they were c oppiced.