THE influence of vapour pressure deficit on leaf water relations of cocos nucifera in northeast brazil
2009
Passos, E.E.M. | Prado, C.H.B.A. | Aragao, W.M.
Daily courses of leaf gas exchange and leaf water potential (psi(leaf)) 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 (VPD(air)), psi(leaf) and VPD(air), leaf transpiration (E) and gs, and E-Ψ(leaf). Despite these similar relationships between sites, stronger correlations involving gs-VPD(air) and E-Ψ(leaf) were found at the semi-arid site, where whole-plant hydraulic conductance (gp) was correlated significantly with VPD(air). In addition, at the semi-arid site, only, the net photosynthesis (P(N)) was not correlated with E and Ψ(leaf), and the intrinsic water use efficiency (WUEi) was disconnected from VPD(air) and Ψ(leaf). The different behaviour of leaf gas exchange and Ψ(leaf) between sites was probably caused by low gs in response to high VPD(air) 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 VPD(air). The atmospheric water stress will probably reinforce the strength of connection among water relation variables (E, Ψ(leaf), gs, gp, and VPD(air)), but it will disrupt the linear relationship between net CO2 assimilation and leaf water relations such as P(N)-E, P(N)-Ψ(leaf), WUEi-VPD(air) and WUEi-Ψ(leaf).
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