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Home Publications National Nursery Proceedings 1990 Seedling Moisture Status

Seedling Moisture Status

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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Author(s): W. Lopushinsky

Publication: National Nursery Proceedings - 1990

Event: Combined Meeting of the Western Forest Nursery Associations
1990 - Roseburg, OR