Southern Research Station

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

Author: Murthy, Ramesh; Zarnoch, Stanley J.; Dougherty, P.M.

Date: 1997

Source: Plant, Cell and Environment, Vol. 20: 558-568

Description: 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.

Keywords: Pinus taeda L., elevated CO₂, net photosynthesis, repeated measure analysis, stomatal conductance

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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