Canopy Photosynthesis and Water-Use Efficiency in a Deciduous Forest

Publisher Website
Google Scholar
Abstract
The short-term canopy photosynthesis and water-use efficiency of a deciduous forest were measured with the eddy correlation method. Canopy photosynthetic rates were strongly dependent on photosynthetically active radiation and were highly correlated with transpiration. These rates were not correlated with vapour presure deficit, air temperature and stomatal resistance since limiting conditions were not encountered. Water-use efficiency was found to be dependent on vapour pressure deficit but was independent of net radiation. Measurements of canopy photosynthetic rates and water-use efficiency were compared with theoretical estimates. Canopy photosynthesis was computed by coupling the leaf photosynthesis model of Marshall and Biscoe (1980) with the canopy radiative transfer model of Baldocchi and Hutchison (1986). Considering the simplicity of the canopy photosynthesis model, the overall agreement between measured and computed values was reasonable. Water-use efficiency measurements agreed well with values computed with the model of Sinclair, Tanner and Bennett (1984). Canopy-atmosphere gas exchange rates were lower than values commonly observed over agricultural crops. This was partly because deciduous forest is aerodynamically rougher than agricultural crops and deciduous trees have a greater canopy stomatal resistance than crops. The ratio between atmospheric CO2 uptake and canopy photosynthesis was different from that commonly measured over agricultural crops. This is because the floor of a deciduous forest has more detritus than an agricultural crop, which allows greater CO2 efflux from the forest floor.