Will stomatal responses to humidity and carbon dioxide constrain tropical forest productivity as atmospheric carbon dioxide rises?

Moist tropical forests play an important role in the global carbon cycle. They contain about half the carbon stored in terrestrial plant biomass, and perform about one third of terrestrial net primary production. I propose research on two physiological processes that could have important consequences for how tropical trees respond to rising atmospheric carbon dioxide. The first is stomatal responsiveness to the humidity difference between the leaf interior and air outside the leaf. The second is an interaction between nutrient acquisition and transpiration rate. Both processes have potential to constrain growth responses of tropical forest trees to rising atmospheric carbon dioxide.