Stomatal response to nonhydraulic root-to-shoot communication of partial soil drying in relation to foliar dehydration tolerance

This paper culminates a series of works to: ( I) compare stomatal response of several temperate. deciduous tree species to nonhydraulic root-to-shoot signals of soil drying; and (2) test whether sensitivity to nonhydraulic signaling is allied with drought avoidance/tolcrance tendencies of species. Saplings were grown with roots divided between two pots. Three treatments were compared: half of the root system watered and half droughted (WD); half of the root system watered and half-severed (WS); and both halves watered (WW). Drying about half of the root system caused marked nonhydraulically induced declines in stomatal conductance (g,) in Nyssa sylvatica and Acer saccharum but only slight declines in Quercus alba, Q. rubra, Q prinus and Q. acutissima. Declines in g(s) were significantly correlated with declining soil matric potential (Psi(m)) in three species. Soil Psi(m) when g(s) of WD plants was 80% of WS controls varied from a high of - 0.03 MPa in A. saccharum to a low of - 0.18 MPa in Q. alba. Neither lethal leaf water potential nor osmotic adjustment was significantly correlated across all species with any measure of stomatal sensitivity to the nonhydraulic root-to-shoot signal. however, species showing considerable osmotic adjustment also tended to show little inhibition of g,. Additionally, species showing little or no foliar osmotic adjustment also showed high stomatal sensitivity to nonhydraulic drought signaling, as indicated by relatively large changes in g. per unit change in soil Psi(m). Stomatal sensitivity to nonhydraulic drought signaling appears mechanistically linked to a limited extent with characteristics that define relative species drought tolerance. (C) 2002 Elsevier Science B.V. All rights reserved.