Leaf- and stand-level responses of a forested mesocosm to independent manipulations of temperature and vapor pressure deficit

Alterations in temperature (T) and vapor pressure deficit (VPD) strongly influence gas exchange, but because VPD is highly influenced by T, the effects of these two factors are difficult to separate.Here, the concomitant effects of T and VPD on CO2 uptake, stomatal conductance, and transpiration at leaf- and canopy-levels were examined for a stand of trees (Populus deltoides) enclosed within large mesocosms. T and VPD were independently altered to yield a factorial combination of treatments of low (24 degrees C) or high (30 degrees C) T and low (0.75) or high (1.75 kPa) VPD. Traditional leaf-level gas exchange measurements were compared with whole-canopy exchange to verify typical scaling methods.