Modifying stomatal conductance delays dehydration but not postharvest needle abscission in Abies balsamea

Postharvest needle abscission poses a significant challenge to the balsam fir (Abies balsamea L.) Christmas tree industry. Root detachment, and other postharvest handling and transporting factors, lead to a progressive dehydration leading to postharvest needle loss. If this were so, reducing the transpiratory wa- ter loss through regulating stomata would be expected to reduce dehydration extending needle retention. This study explored this hypothesis through manipulation of balsam fir stomata using chemical treatments to determine the effect on water uptake, relative water content, and needle abscission. Branches were col- lected from 70 trees and immediately applied a postharvest treatment of water (control), ABA, fluoridone, BAP, theophylline, potassium nitrate, or dopamine. Stomatal conductance decreased by 27% after applica- tion of ABA and increased by 24%, 17%, and 18% by fluoridone, BA, and potassium nitrate, respectively. Consequently, the ABA treatment resulted in a significantly lower water uptake while fluoridone, BAP, and potassium nitrate all increased water uptake. Despite changes in stomatal conductance and water uptake, there were no significant changes in needle retention. Needle abscission commenced after an average of 12.5 days from postharvest treatment application and reached 100% completion after an average of 71.9 days. It is possible to manipulate stomatal conductance and water uptake through chemical methods, but such a manipulation does not guarantee superior needle retention. It is proposed that deficiency of certain hormonal signals originating from roots may play a critical role in postharvest needle abscission.