Modelling the effects of elevated atmospheric CO2 on crown development, light interception and photosynthesis of poplar in open top chambers

An open-top chamber experiment was carried out to examine the likely effects of elevated atmospheric CO₂] on architectural as well as on physiological characteristics of two poplar clones ( Populus trichocarpa × P. deltoides clone Beaupré and P. deltoides × P. nigra clone Robusta). Crown architectural parameters required as input parameters for a three-dimensional (3D) model of poplar structure, such as branching frequency and position, branch angle, internode length and its distribution pattern, leaf size and orientation, were measured following growth in ambient and elevated CO₂ ] (ambient + 350 μmol mol^–1) treated open-top chambers. Based on this information, the light interception and photosynthesis of poplar canopies in different CO₂] treatments were simulated using the 3D poplar tree model and a 3D radiative transfer model at various stages of the growing season. The first year experiments and modelling results showed that the CO₂] enrichment had effects on light intercepting canopy structure as well as on leaf photosynthesis properties. The elevated CO₂] treatment resulted in an increase of leaf area, canopy photosynthetic rate and above-ground biomass production of the two poplar clones studied. However, the structural components responded less than the process components to the CO₂] enrichment. Among the structural components, the increase of LAI contributed the most to the canopy light interception and canopy photosynthesis; the change of other structural aspects as a whole caused by the CO₂] enrichment had little effect on daily canopy light interception and photosynthesis.