Abstract:
A series of experiments was designed to investigate differential
flood-tolerance and the phenomenon of flood-induced stomatal closure
of several fruit tree species. The first two experiments were conducted
with potted plants submerged outdoors 5-10 cm above the soil line.
Plant morphology, growth, leaf conductance (cL), and soil oxygen diffusion
rate (ODR) were monitored. Differential waterlogging tolerance
of major fruit tree rootstocks tested from high to low was as follows:
Pyrus betulaefolia > Pyrus calleryana = Cydonia oblonga cv. Provence
BA 29 > Pyrus communis (Bartlett seedling) > Pyrus communis cv. Old
Home X Farmingdale 97 (OH X F 97) = Malus domestica cv. Mailing Merton
106 > Prunus persica (Halford or Lovell seedling).
Grafting 'Bartlett' scions on the 4 major pear rootstocks listed
above did affect plant performance in terms of growth and cL but did
not alter overall survivability. Stomatal closure for each species
was associated with a specific ODR. Limitations of cL as a screening
tool are discussed in the thesis.
Solution culture experiments conducted in the greenhouse revealed
that anaerobic-induced stomatal closure was not a function of reduced
leaf water potential but was related to a reduction in root hydraulic
conductivity (Lp). Two lines of evidence suggest that increased root
resistance to water flow was predominantly in the longitudinal and 10⁻⁴
not the radial direction. Firstly, 10 M abscisic acid (ABA)
applied to intact OH X F 97 roots in solution culture enhanced Lp
of plants previously exposed to aerobic but not anaerobic conditions.
Secondly, excising feeder roots of anaerobically treated roots,
thereby exposing xylem tissue directly to the nutrient solution, did
not revive Lp to rates observed for intact aerobically treated roots.
A basipetal progression of xylem plugging occurred with increasing
duration of anaerobiosis.
The promotion of volume flux (Jv) observed for aerobically
treated OH X F 97 was studied. All 3 concentrations of ABA tested
enhanced Jv within 10-20 minutes with the effect leveling off after
1% hours. Analysis of the xylem fluid revealed a slight change in
osmotic potential and solute flux, far smaller than the driving force
required to significantly alter Jv. It is concluded that only
changes in Lp can account for this phenomenon.
