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Effects of chlorine deficiency in the field on leaf gas exchanges in the PB 121 coconut hybrid

Braconnier S., Bonneau X.. 1998. In : CIRAD-C. Contract TS3*CT92-0132. "Coconut-based farming systems. Operational and economic analysis models". Annexes = [Contrat TS3 CT92 0132. "Systèmes de culture en association avec le cocotier. Modèles de fonctionnement et d'analyse économique". Annexes]. Paris : CIRAD-CP, 15 p..

A study of leaf gas exchanges during the dry season and rainy season confirmed the importance of the Cl- ion in coconut. In the dry season, compared to a control, chloride deficiency led to lower stomatal conductance in coconut, hence a reduction in leaf gas exchanges. This resulted in less intense net photosynthesis and transpiration, which accounted for the poorer drought tolerance of Cl- deficient palms. During the dry season, even if not very intense, coconut palms that were not Cl- deficient maintained and even increased their stomatal conductance. This enabled them to increase leaf transpiration, hence responding to the increase in evaporative demand and maintaining a high level of net assimilation. Conversely, deficient palms reduced their stomatal conductance, leading to a drop in transpiration and in net photosynthesis. Observations during the rainy season failed to reveal any effect of chloride deficiency on intrinsic photosynthesis. The Cl- ion therefore seems to act primarily during the dry season, and in stomatal regulation.

Mots-clés : cocos nucifera; hybride; résistance à la sécheresse; carence minérale; chlorure; photosynthèse; transpiration; Échange gazeux; stomate; conductance stomatique; indonésie; cocotier pb 121

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