Experimental control of water status in an apple orchard

Drought acclimation of two deciduous tree species of different layers in a temperate forest canopy

“…AugØ et al 1998;Croker et al 1998;Loewenstein and Pallardy 1998a). The regulation of water relations in trees changes with age (Jones et al 1983;Whitehead 1998). There are fewer comparative data (Bahari et al 1985;Loewenstein and Pallardy 1998b) about the water use of mature trees of different canopy layers.…”

Estimation of an effective soil water potential at the root surface of transpiring plants

“…Measurements of t//, made predawn (e,g. Running, 1976), when i/*, is thought to estimate a mean 4'^ over the root zone (Slatyer, 1967), therefore have some advantages, A further argument against the use of i/^, is that some plants when subjected to soil water deficits control \pŝ o efficiently by stotnatal closure that plants with very inadequate water supply can have the same (Bates & Hall, 1981) or even higher (Jones et al, 1983) water potentials than well-watered controls. In such cases i/', is not a good measure of stress.…”

“…The method is based on the estimation of an average ip^ at the toot surface using the familiar Ohm's law analogue which may be written in the form (see e.g. Jones, 1983) (I) 0t4O-7791/83/l 100-0671 $02,00 © 1983 Blackwell Scientfie Publications where E is the transpiration rate per plant (g s ') and Rp (MPasg"') is the total hydraulic resistance within the plant. This simple steady-state Mumped paratneter' model with a constant .^p has been found adequate to fit experimental data for tnany species, especially woody ones {see e.g.…”

“…Elfving, Kaufmann & Hall, 1972;Barrs, 1973;Camacho-B, Kaufmann & Hall, 1974b;Landsberg et al, 1975), In tnany herbaceous species, however, a variable Rt hat decreases with inereasing E has been needed to fit observed data {.see e.g. Tinklin & Weatherley, 1966;Barrs, 1973;Camacho-B, Hall & Kaufmann, 1974a;Biscoe, Cohen & Wallace, 1976;Jones, 1978;Black, 1979), An analogous equation can be written for evaporation from plant leaves {see Jones, 1983), In this case the evaporation rate per unit leaf area {E^, gm"^ s"') is proportional to the water vapour pressure difference between the evaporating surfaces within the leaf and the ambient air {e^ -ej according to:…”

“…Measurements of r/',, g, and soil water content were made in 1979 on a 3-year-old apple (Malus puniita (Mill,)) orchard (Bramley's Seedling on M,9 rootstock), grown with overall herbicide treatment, and in 1982 on the same orchard. Full details of the experiment are given elsewhere (Jones et al, 1983), Results are presented for three of the treatments: (a) control, which was irrigated with gr-ound-level minisprinklers maintaining soil water content close to field capacity; (b) full drought, which was unirrigated and a large proportion of incident rainfall excluded from the root zone by under-tree polyethylene 'tents' erected in the first (1982) or second (1979) week of June; (c) late drought, which was irrigated until the covers were installed in late July, Soil moisture contents were measured using a neutron-probe, taking the mean of readings for access tubes at 0,5 m and 1,5 m from the tree row.…”