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

Abstract

This paper culminates a series of works to: (1) 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/tolerance 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 s) 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 ( Ψ m) in three species. Soil Ψ 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 s. 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 s per unit change in soil Ψ m. Stomatal sensitivity to nonhydraulic drought signaling appears mechanistically linked to a limited extent with characteristics that define relative species drought tolerance.