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Stomatal resistance and transpiration rates of shaded and unshaded cacao trees

by Valle, R.R; Silva, W.S. da; Miranda, R.A.C.
Publisher: Jul-Set 1987Subject(s): THEOBROMA CACAO | ESTOMA | TRANSPIRACION | BRASILOnline Resources: En In: Revista Theobroma (Brasil) v. 17(3) p. 175-187Summary: Measured leaf stomatal resistance (Rs) were used to estimate transpiration rates (TR) on different canopy layers of shaded and unshaded cacao trees. Data taken on a sunny and an overcast day were used to compare the stomatal and transpirational behavior of the canopies. Stomatal resistances on the overcast day for the unshaded tree increased gradually from the upper to the lower canopy layer, with a consequent decrease in TR. The Rs for the leaves of the shaded tree were lower for the bottom than for the upper canopy layer leaves. This was presumably due to the higher irradiance received by the lower canopy layers. Greater irradiance in the bottom layers of the shaded tree was caused by the shade of an Erythrina fusca that impeded light penetration to the upper layers even at lower solar angles. Stomatal resistances and TR, on the sunny day for the unshaded tree and between two areas of the upper canopy on the shaded tree, were closely correlated to irradiance. Estimated daily TR, for the shaded tree, were of the same order of magnitude of TR computed by other authors by different methods
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Measured leaf stomatal resistance (Rs) were used to estimate transpiration rates (TR) on different canopy layers of shaded and unshaded cacao trees. Data taken on a sunny and an overcast day were used to compare the stomatal and transpirational behavior of the canopies. Stomatal resistances on the overcast day for the unshaded tree increased gradually from the upper to the lower canopy layer, with a consequent decrease in TR. The Rs for the leaves of the shaded tree were lower for the bottom than for the upper canopy layer leaves. This was presumably due to the higher irradiance received by the lower canopy layers. Greater irradiance in the bottom layers of the shaded tree was caused by the shade of an Erythrina fusca that impeded light penetration to the upper layers even at lower solar angles. Stomatal resistances and TR, on the sunny day for the unshaded tree and between two areas of the upper canopy on the shaded tree, were closely correlated to irradiance. Estimated daily TR, for the shaded tree, were of the same order of magnitude of TR computed by other authors by different methods

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