Leaf photosynthesis of Betula albosinensis seedlings as affected by elevated CO 2 and planting density

Abstract

Birch ( Betula albosinensis Burk.) seedlings were grown under two CO 2 concentrations, 350 μmol mol −1 (ambient CO 2) and 700 μmol mol −1 (elevated CO 2), and in two planting densities, 32 plants/m 2 (low density, LD) and 72 plants/m 2 (high density, HD). The objectives were to characterize the responses of leaf photosynthesis to long-term elevated CO 2 in birch seedlings in different planting densities, and to assess whether elevated CO 2 regulates the photosynthetic capacity of leaves, in terms of nitrogen concentration (N), the activity of ribulose bisphosphate carboxygenase (Rubisco), the photosynthetic efficiency of Rubisco and the concentration of nonstructural carbohydrates (TNC). In both planting densities, the leaves of birch seedlings grown under elevated CO 2 but measured at 350 μmol mol −1 CO 2 had a lower leaf N concentration, net CO 2 assimilation rate ( A), transpiration ( E) and stomatal conductance ( g s), and a higher water use efficiency (WUE) than those of birch seedlings both grown and measured under ambient CO 2 concentration. On the other hand, the values of A, E, g s and WUE were significantly affected by planting density under ambient CO 2, whereas these parameters were not affected by planting density under elevated CO 2. In contrast, the levels of sucrose, soluble sugars, starch and TNC in the leaves were not significantly affected by planting density under ambient CO 2, whereas these parameters were significantly affected by planting density under elevated CO 2. Our results demonstrated that there are different acclimations of leaf photosynthesis in birch seedlings, as affected by elevated CO 2 and planting density, and they highlighted the importance of the CO 2 level and planting density for the physiological ecology of woody plants.