The Pressure Is On - Epiphyte Water-Relations Altered Under Elevated CO.

Vascular epiphytes are a major biomass component of forests across the globe and they contribute to 9% of global vascular plant diversity. To improve our understanding of the whole-plant response of epiphytes to future climate change, we investigated for the first time both individual and combined effects of elevated CO (560 ppm) and light on the physiology and growth of two epiphyte species [ (CAM) and (C3)] grown for 272 days under controlled conditions. We found that under elevated CO the difference in water loss between the light (650 μmol ms) and shade (130 μmol ms) treatment was strongly reduced. Stomatal conductance ( ) decreased under elevated CO, resulting in an approximate 40-45% reduction in water loss over a 24 h day/night period under high light and high CO conditions. Under lower light conditions water loss was reduced by approximately 20% for the CAM bromeliad under elevated CO and increased by approximately 126% for the C3 fern. Diurnal changes in leaf turgor and water loss rates correlated strong positively under ambient CO (400 ppm) and high light conditions. Future predicted increases in atmospheric CO are likely to alter plant water-relations in epiphytes, thus reducing the canopy cooling potential of epiphytes to future increases in temperature.