Stomatal Response to Environmental Variables in Two Tropical Forest Species During the Dry Season in Nigeria

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Abstract
Measurements of stomatal conductance using a null-balance diffusion porometer were made on Gmelina arborea Roxb. and teak [Tectonia grandis L.] on 6 days during the dry season in Nigeria. Stomatal conductance increased rapidly in the early morning and decreased after midday in both species but values in Gmelina were less than those in teak. Leaf water potential, measured with a pressure chamber, was usually lower in Gmelina than in teak. Stomatal conductance in both species was dominantly controlled by irradiance and air saturation deficit and a model, relating stomatal conductance to these 2 variables accounted for more than 80% of the variation in the measurments. The Penman-Monteith equation was used to calculate transpiration rates from measured stomatal conductances and environmental variables. Transpiration rates using conductances predicted from the model agreed closely with the calculated ones. Hydraulic resistances were similar for both species. The use of these measurements in predicting transpiration rates by the species from weather station data is discussed.