Net Photosynthesis and Stomatal Conductance of Peach Seedlings and Cuttings in Response to Changes in Soil Water Potential

Greenhouse-grown peach [ Prunus persica (L.) Batsch] seedlings and cuttings were drought-stressed by reducing soil water potential (ψ soil ) from field capacity (FC) to permanent wilting point, (PWP). Mean ψ soil and leaf water potential (ψ leaf ) were correlated with measurements of stomatal conductance (g s ), net photosynthetic (Pn) rate, and vapor pressure deficit (VPD). Decreasing Pn and g s trends were noted as ψ soil decreased. Photosynthetic rate and g s were significantly reduced at ψ leaf more negative than −1.5 MPa. Values of Pn and g s were more highly correlated to ψ leaf than ψ soil . A midday depression in Pn rates began 2 hr earlier and peak rates were at least 50% lower when ψ soil was more negative than −0.05 MPa. The correlation coefficient ( r ) between ψ leaf and ψ soil and between g s and Pn rate at different ψ soil was above 0.70. The r values decreased as soil and plant water potential became more negative. Stomatal conductance peaked at optimal ψ soil (FC) 2 hr following sunrise. Photosynthetic rate peaked at a ψ soil around −0.05 MPa 4 hr after sunrise.