PERFORMANCE OF INTERIOR SPRUCE SEEDLINGS TREATED WITH ABSCISIC-ACID ANALOGS

This research examined the performance of interior spruce (Picea glauc a (Moench) Voss x Picea engelmannii Parry ex Engelm.) seedlings, each group treated with one of nine abscisic acid (ABA) analogs, during the initial stages of seedling establishment under a range of environment al conditions. Interior spruce seedlings were removed from frozen stor age, ABA analog treatments were immediately applied, and seedlings wer e tested under low root temperature or moderate drought cycle conditio ns. Alternatively, seedlings were removed from frozen storage and held until bud break had occurred before ABA analog treatments were applie d. These seedlings were then tested under severe drought or optimum en vironmental conditions. ABA analog 1, followed by ABA analog 2, had th e most consistent performance of the nine tested ABA analogs under all combinations of environmental test conditions. These ABA analogs redu ced needle conductance for 7-9 days when seedlings were tested under l ow root temperature conditions with only a reduction in net photosynth esis on the first day of testing. During three successive moderate dro ught cycles, seedlings treated with ABA analogs 1 and 2 had partial st omatal closure, thereby increasing mean shoot water potential by aroun d 50%. During a severe drought, ABA analog 1 caused partial stomatal c losure, which allowed seedlings to maintain a mean shoot water potenti al of greater than -3.0 MPa and a positive net photosynthesis up to 8 days longer than control seedlings. Under optimum environmental condit ions, ABA analogs 1 and 2 reduced needle conductance for up to 7 days, with net photosynthesis reduced for 1 day. Root growth was not advers ely affected in seedlings treated with any of the ABA analogs prior to bud break. However, when seedlings were treated after bud break, all ABA analogs reduced growth of long roots (>4.0 cm) by approximately 60 %. ABA analogs 1 and 2 delayed bud break by 4 days, when compared with control seedlings. Results are discussed in reference to the establis hment process of spruce seedlings on reforestation sites.