Influence of temperature and nitrogen on photosynthesis in early and late successional tree species of the Great Lakes region: implications for forest carbon uptake.

Abstract

The interactions between forests and climate are becoming an increasingly important global processes. Therefore, forest carbon uptake, by means of photosynthesis, and the factors that affect it are important parameters for climate models. Modeling photosynthesis requires values of rate of carboxylation (Vcmax) and electron transport capacity (Jmax), both of which can be derived from gas exchange measurements based on the Farquhar, von Caemmerer and Berry (FvCB) model of photosynthesis. In this study, A/Ci curve analysis was done in Northern lower Michigan for two late successional species, red oak (Quercus rubra) and red maple (Acer rubrum), and one early successional species, bigtooth aspen (Populus grandidentata). Samples were taken across different canopy levels and temperatures to determine the effects on photosynthetic activity. It was found that for Vcmax, species was not significant and canopy was only significant for red oak. For Jmax, species was significant and canopy was significant for both red oak and red maple. Further analysis suggested that the Jmax species differences were likely attributable to canopy differences These results suggest the importance of canopy structure in determining the photosynthetic activity, and therefore carbon uptake, of forests. Consequently, it also implies that changes to forest composition have the potential to cause changes in the carbon uptake of the forest.