© 1997 Heron Publishing—Victoria, Canada
Effect of elevated carbon dioxide concentration and root restriction on net photosynthesis, water relations and foliar carbohydrate
status of loblolly pine seedlings
R. E. Will and R. O. Teskey
School of Forest Resources, University of Georgia, Athens, GA 30602, USA / Received July 24, 1996
Summary
To determine the effects of CO2-enriched air and root restriction on photosynthetic capacity, we measured net photosynthetic rates of 1-year-old loblolly
pine seedlings grown in 0.6-, 3.8- or 18.9-liter pots in ambient (360 µmol mol–1) or 2× ambient CO2 (720 µmol mol–1) concentration for 23 weeks. We also measured needle carbohydrate concentration and water relations to determine whether
feedback inhibition or water stress was responsible for any decreases in net photosynthesis. Across all treatments, carbon
dioxide enrichment increased net photosynthesis by approximately 60 to 70%. Net photosynthetic rates of seedlings in the smallest
pots decreased over time with the reduction occurring first in the ambient CO2 treatment and then in the 2× ambient CO2 treatment. Needle starch concentrations of seedlings grown in the smallest pots were two to three times greater in the 2×
ambient CO2 treatment than in the ambient CO2 treatment, but decreased net photosynthesis was not associated with increased starch or sugar concentrations. The reduction
in net photosynthesis of seedlings in small pots was correlated with decreased needle water potentials, indicating that seedlings
in the small pots had restricted root systems and were unable to supply sufficient water to the shoots. We conclude that the
decrease in net photosynthesis of seedlings in small pots was not the result of CO2 enrichment or an accumulation of carbohydrates causing feedback inhibition, but was caused by water stress.
Keywords:
feedback inhibition, needle starch, needle sugar, Pinaceae, Pinus taeda, water stress.
