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Proceedings of Past Forest Nursery Association Meetings:

Seedling Moisture Status
Lopushinsky, W.
1990: Roseburg, OR
The water status of nursery tree seedlings can be deter-
mined by measuring seedling water content, and by liquid
equilibration, psychrometric, and pressure chamber tech-
niques. The latter two techniques measure water poten-
tial, an expression of the free energy of water which is
closely related to physiological functions. Liquid equili-
bration methods are laborious, time consuming, and
imprecise. Water potential can be measured very accu-
rately with thermocouple psychrometers, but long equili-
bration times and other technical requirements make this
method best suited for laboratory use. The hydraulic leaf
press is easy to use and economical; however, endpoints
vary with the type of tissue and with the level of water
potential. The best choice for nursery work is the pressure
chamber. With it, measurements are fast, simple, and
accurate. It can be used to obtain estimates of osmotic
and turgor potential, measure the hydraulic conductivity
of root systems, and detect cold injury in roots. The pres -
sure chamber is being used to schedule irrigation and, in
some cases, to monitor water stress during lifting and
packing. During seedling growth, predawn water poten-
tials should be maintained above -0.5 MPa. Cold and
drought hardiness can be increased by exposure to mod-
erate water stresses (-0.5 to -1.0 MPa), but conditioning
procedures and responses have not been studied exten-
sively in northwest conifers. Available data indicate that
seedling water potentials down to -2.0 MPa during lifting
will not adversely affect seedlings, provided they are
moistened prior to storage. Interpretation of seedling
water potentials requires that consideration be given to
the magnitude of the water stresses, their duration, stage
of seedling growth or dormancy, the species involved,
and seedling vigor.
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