| Plant performance and root characteristics of container-grown Photinia x Fraseri were studied under varying irrigation regimes. Rooted cuttings were transplanted into Metro-mix 500 (W. R. Grace and Co.) for each experiment. Treatments were based on management allowed deficit (MAD) irrigation, which established various levels of water potential and air-filled porosity in the growing medium. In addition, treatments included various levels of evapotranspirational (ET) demand (i.e., winter vs. summer, greenhouse vs. field).;Plant performance was maximized when water potentials in the growing remained high, but air-filled porosity was maintained between 16% and 23% by volume. Water potential of the medium was a major factor in plant performance under high ET demands; however, under low ET demands, the effect of high water potential was mitigated by a reduction of air-filled porosity in the medium. High water potential nearing that at container capacity, reduced air-filled porosity under these conditions caused a reduction in growth.;Increasing irrigation frequency reduced gas exchange of the medium. Lower concentrations of O;Plant water status was not significantly reduced until moisture deficit levels exceeded 40%. Transpiration was reduced by approximately one-third in plants where medium moisture was allowed to deplete to 50% of available moisture. Leaf water potential was also decreased significantly. Plants exposed to 75% and 95% moisture deficits showed a more severe reduction in transpiration, increase in stomatal resistance and decrease in leaf water potential.;Plant water-use per unit shoot extension (W... |
