MODELING 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 e ffects of elevated atmospheric [CO2] on architectural as well as on ph ysiological characteristics of two poplar clones (Populus trichocarpa x P. deltoides clone Beaupre and P. deltoides x P. nigra clone Robusta ). Crown architectural parameters required as input parameters for a t hree-dimensional (3D) model of poplar structure, such as branching fre quency and position, branch angle, internode length and its distributi on pattern, leaf size and orientation, were measured following growth in ambient and elevated [CO2] (ambient + 350 mu mol mol(-1)) treated o pen-top chambers. Based on this information, the light interception an d 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 experime nts and modelling results showed that the [CO2] enrichment had effects on light intercepting canopy structure as well as on leaf photosynthe sis properties. The elevated [CO2] treatment resulted in an increase o f leaf area, canopy photosynthetic rate and above-ground biomass produ ction of the two poplar clones studied. However, the structural compon ents responded less than the process components to the [CO2] enrichmen t. Among the structural components, the increase of LAI contributed th e most to the canopy light interception and canopy photosynthesis; the change of other structural aspects as a whole caused by the [CO2] enr ichment had little effect on daily canopy light interception and photo synthesis.