Experimental Agriculture

Research Article

THE INFLUENCE OF VAPOUR PRESSURE DEFICIT ON LEAF WATER RELATIONS OF COCOS NUCIFERA IN NORTHEAST BRAZIL

E. E. M. PASSOSa1, C. H. B. A. PRADOa2 c1 and W. M. ARAGÃOa1

a1 Embrapa Tabuleiros Costeiros, Av. Beira Mar 3250, Aracaju, SE, Brasil, 49025-040

a2 Universidade Federal de São Carlos, Centro de Ciências Biológicas e da Saúde, Laboratório de Fisiologia Vegetal, Departamento de Botânica, 13565-905, São Carlos, SP, Brasil

SUMMARY

Daily courses of leaf gas exchange and leaf water potential (Ψleaf) of green dwarf coconut palm (Cocos nucifera) were measured in irrigated plantations on the wet coastal plateau and in a dry semi-arid area of northeast Brazil. At both sites, significant correlations were obtained between stomatal conductance (gs) and vapour pressure deficit (VPDair), Ψleaf and VPDair, leaf transpiration (E) and gs, and E-Ψleaf. Despite these similar relationships between sites, stronger correlations involving gs-VPDair and E-Ψleaf were found at the semi-arid site, where whole-plant hydraulic conductance (gp) was correlated significantly with VPDair. In addition, at the semi-arid site, only, the net photosynthesis (PN) was not correlated with E and Ψleaf, and the intrinsic water use efficiency (WUEi) was disconnected from VPDair and Ψleaf. The different behaviour of leaf gas exchange and Ψleaf between sites was probably caused by low gs in response to high VPDair at the semi-arid site. Our results indicate potential for significant alterations in the pattern of leaf gas exchange during future climatic changes with increasing temperature and concomitant increases in VPDair. The atmospheric water stress will probably reinforce the strength of connection among water relation variables (E, Ψleaf, gs, gp, and VPDair), but it will disrupt the linear relationship between net CO2 assimilation and leaf water relations such as PN-E, PNleaf, WUEi-VPDair and WUEi-Ψleaf.

(Accepted September 22 2008)

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