© 1995 Heron Publishing—Victoria, Canada
Offsetting effects of reduced root hydraulic conductivity and osmotic adjustment following drought
M. Rieger
Department of Horticulture, University of Georgia, Athens, GA 30602, USA / Received February 28, 1994
Summary
Root hydraulic conductivity (Lp) and leaf osmotic potential at full turgor (Ψπ,o) were measured in young, drought-stressed and nonstressed peach (Prunus persica (L.) Batsch), olive (Olea europaea L.), citrumelo (Poncirus trifoliata Raf. × Citrus paradisi Macf.) and pistachio (Pistachia integerrima L.). Drought stress caused a 2.5- to 4.2-fold reduction in Lp, depending on species, but Ψπ,o was reduced only in citrumelo and olive leaves by 0.34 and 1.4 MPa, respectively. No differences existed in Lp among species for nonstressed plants. A simple model linking Lp to osmotic adjustment through leaf water potential (Ψ) quantified the offsetting effects of reduced Lp and osmotic adjustment on the hypothetical turgor pressure difference between drought-stressed and nonstressed plants (ΔΨp). For olive, the 2.5-fold reduction in Lp caused a linear decrease in ΔΨp such that the effect of osmotic adjustment was totally negated at Ψ = –3.2 MPa. Thus, no stomatal closure would be required
to maintain higher turgor in drought-stressed olive plants than in nonstressed plants over their typical diurnal range of
Ψ (–0.6 to –2.0 MPa). For citrumelo, osmotic adjustment was offset by reduced Lp at Ψ ≈ –0.9 MPa. Unlike olive, stomatal closure would be necessary to maintain higher turgor in drought-stressed citrumelo
plants than in nonstressed plants over their typical diurnal range of Ψ (0 to –1.5 MPa). Regardless of species or the magnitude
of osmotic adjustment, my analysis suggests that a drought-induced reduction in Lp reduces or eliminates turgor maintenance through osmotic adjustment.
Keywords:
citrumelo, leaf osmotic potential, Olea europaea, olive, peach, pistachio, Pistacia integerrima, Poncirus trifoliata × Citrus paradisi, Prunus persica, stomatal closure, turgor, water relations.
