Seasonal trends of light-saturated net photosynthesis and stomatal conductance of loblolly pine trees grown in contrasting environments of nutrition, water and carbon dioxide

Abstract

Repeated measures analysis was used to evaluate the effect of long-term CO₂ enhancement on seasonal trends of light-saturated rates of net photosynthesis (A_sat) and stomatal conductance to water vapour (g_sat) of 9-year-old loblolly pine (Pinus taeda L.; trees grown in a 2x2 factorial experience mental design of nutrition and water. A significant interaction effect of CO₂ and nutrition on mean A_sat was observed for juvenile foliage. also, juvenile foliage exposed to +350 μmol mol_-1 CO₂ had a higher rate of increase of A_sat between late summer and early autumn. This would lead to a greater potential for recharging carbohydrate reserves for winter. Mature foliage was affected by CO₂, water and nutrient treatments in two ways. First, A_sat was significantly increased as a result of elevated CO₂ in January, a period when stomatal conductance was only 47% of the maximum observed rate. Secondly, the rate of increase of A_sat from winter to early spring was accelerated as a result of both nutrient + water and +350 μmol mol^-1 CO₂ treatments. This accelerated response resulted in a greater potential for photosynthate production during the period when growth initiation occurred. Nutrient, water or carbon dioxide treatments did not significantly alter trends in g_sat for mature or juvenile foliage. A significant nutrient X CO₂ interaction was observed for the mature foliage, suggesting that g_sat increased with increasing CO₂ and nutrition. These results may have important consequences for the determination of the water use efficiency of loblolly pine. In spite of low g_sat in the winter to early spring period, there was a substantial gain in A_sat attributable to elevated CO₂ concentrations.

Citation

Murthy, Ramesh; Zarnoch, Stanley J.; Dougherty, P.M. 1997. Seasonal trends of light-saturated net photosynthesis and stomatal conductance of loblolly pine trees grown in contrasting environments of nutrition, water and carbon dioxide. Plant, Cell and Environment, Vol. 20: 558-568