Influence of climate variables onCyperus papyrusstomatal conductance in Lubigi wetland, Kampala, Uganda

Cyperus papyrus forms highly productive wetlands in tropical Africa, but the environmental control of transpirational water loss in wetlands is poorly understood. The influence of climate variables on papyrus stomatal conductance in dry and wet seasons of the year was investigated in a wetland in Kampala, Uganda, in June–December, 2012. In situ measurements were made of local climate conditions in a papyrus canopy and of bracteole stomatal conductance. Stomatal conductance was highest early in the day and declined as the day progressed, but stomata were more consistently open in the wet season than in the dry season. The daily cycle of stomatal conductance was influenced by temperature, incident radiation and vapour pressure deficit. Stomata were more sensitive to vapour pressure deficit changes during the wet season than in the dry season, closing sharply as vapour pressure deficit increased. This would seem to be a useful strategy for regulating transpiration, as it reduces water loss when the vapour pressure deficit gradient between the leaf intercellular spaces and the atmosphere is greatest.