Stomatal sensitivity of six temperate, deciduous tree species to non-hydraulic root-to-shoot signalling of partial soil drying

Abstract

The objectives of this study were to (1) characterize stomatal response of six deciduous tree species to non-hydraulic, root-sourced signals of soil drying, and (2) test whether species sensitivity to non-hydraulic signalling is allied with their drought avoidance and tolerance profiles. Saplings were grown with roots divided between two pots. Three treatments were compared: one half of the root system watered and half droughted (WD), one half of the root system watered and half severed (WS), both halves watered (WW). Drying about half of the root system caused nonhydraulic declines in stomatal conductance (g_s) in all species, with g_s of WD plants reduced to from 40% to 60% of WS controls. Declines in stomatal conductance were closely related to declining soil matric potential (ψ_m) between −0.01 and −0.10 MPa. Soil ψ_m required to cause declines in g_s of WD plants to 80% of WS controls varied from a high of −0.013 to a low of −0.044 MPa. Stomatal inhibition varied somewhat with leaf age in half of the species. Leaf osmotic potentials during soil drying were mostly similar among treatments. Although stomatal sensitivity to the nonhydraulic, root-sourced signal (characterized as decline in g_s per unit decline in soil ψ_m) was not closely correlated with previously identified lethal leaf water potentials or capacity for osmotic adjustment, species having the highest stomatal sensitivity also had the least dehydration tolerance. This suggests that stomatal sensitivity to non-hydraulic root signals may be mechanistically linked to a limited extent with other characteristics defining relative species drought tolerance.