Seasonal changes in physiological status, cold storage tolerance and field performance of hybrid larch seedlings in Ireland

Abstract

The physiological condition at the time of lifting between October and May, 1995/96 and 1996/97 (and after cold storage until May, 1996/97) of hybrid larch (Larix x eurolepis Henry) seedlings grown in Ireland was assessed. The seasonal pattern of cold hardiness acclimation and deacclimation was similar in 1995/96 and 1996/97, bur deacclimation occurred 4-5 weeks earlier in the milder 1996/97 season. The pattern of change in shoot tip dry weight fraction was similar during the deacclimation phase each year, but there were differences during acclimation between years. Root electrolyte leakage (REL) declined and remained low from November to February, 1996/97; thereafter, REL increased until May. REL remained low during most of the November to April period in the colder 1995/96. The seasonal pattern of root growth potential (determined in a glasshouse) was similar each year; it declined and remained near zero from November to January, then increased rapidly to high values by March/April. The first-year field performance of seedlings planted soon after lifting in 1995/96 and 1996/97 (and after cold storage until May in 1996/97) was assessed. Similarly, field performance of seedlings from other nurseries planted in 1992/93 and 1994/95 was evaluated. Survival and/or height increment was best for stock that was freshly planted from about October until February/early March. Although survival was good, height increment was poor for cold-stored stock planted in May. Lifting for field planting under operational conditions should begin when cold hardiness (It20) is greater than -15°C (in these experiments equivalent to late October/early November). Field planting should cease when plants deharden to temperatures warmer than this (equivalent to early February/early March).