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21 - Stomatal conductance in tomato responds to air humidity

Published online by Cambridge University Press:  04 August 2010

I. Ferreira
Affiliation:
DER, Institute Superior de Agronomia, Universidade Técnica de Lisboa, Tapada daAjuda, 1399 Lisboa Codex, Portugal.
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Summary

SUMMARY

Stomatal conductance and water potential were recorded in an irrigation experiment in which air humidity and soil water were varied. The results suggest that stomata responded to changes in air humidity irrespective of soil water availability when the predawn leaf water potential is above some critical level used for irrigation scheduling.

INTRODUCTION

In previous experimental work the variation of evapotranspiration (ET), stomatal conductance (gs) and predawn leaf water potential (Ψ) were studied in an irrigated tomato crop in Portugal; the midday stomatal conductance decreased when a Ψ of -0.4 MPa was attained (Katerji, Itier & Ferreira, 1988). Above this limit there was considerable scatter and no clear relationship between these variables existed. In spite of that, ET decreased as soon as one day after irrigation (Itier, Ferreira & Katerji, 1988) and this was associated with a decrease in gs (Ferreira, 1987). What is the reason for stomatal closure so soon after irrigation? Two hypotheses were considered: 1) local advection reduces the air humidity conditions close to the leaves inducing stomatal closure and 2) the roots send a signal to the shoot (as described by Davies & Mansfield, 1988) and induce stomatal closure.

MATERIALS AND METHODS

Measurements were made in the field in Coruche, Portugal (lat 38°57′, long 8°32′, alt 30m). Tomato plants (Lycopersicon esculentum Mill.) were planted in a loamy soil in rows for furrow irrigation. Four plots (A, B, C and D) were used, each with a 50 m fetch in the center (Fig. 1).

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Publisher: Cambridge University Press
Print publication year: 1993

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