Testing water potential in peach trees as an indicator of water stress

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Abstract
Water potential has been measured on transpiring (ψL = leaf water potential) and non-transpiring (ψS = stem water potential) leaves in peach trees irrigated at 50% and 100% actual evapotranspiration (AET). The calculated difference between ψS and ψL (ψS – ψL= Δψ), which gives a measure of leaf transpiration, was studied, and only slight differences in ψL values between the two treatments were observed. This non-sensitivity of ψL is discussed. In contrast, before irrigation, ψS was significantly more negative in the 50% AET regime than in the 100% AET regime, implying a decrease in Ay values. This suggests decreased leaf transpiration caused by stomatal closure. Differences in ψSvalues disappeared after the irrigations. The sensitivity of ψS and Δψ to alternation of drying periods and irrigations allows the use of these parameters for the timing of irrigation. A method involving the use of the relation between ψL and Ηψ in non-limiting soil water conditions is proposed.