Determination of Deacclimation Temperature and Duration for Creeping Bentgrass and Annual Bluegrass.

The occurrence of freeze-thaw events during winter months may lead to cold deacclimation and predispose plants to freezing injury.  Research from controlled environment studies and anecdotal observations suggest that annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis stolonifera L.) differ in their susceptibility to freezing injury, which may be influenced by interspecific differences in the capacity to withstand deacclimation.  Therefore, the objectives of this research were to compare the sensitivity of annual bluegrass and creeping bentgrass to deacclimation in response to a combination of different above-freezing temperature and duration treatments. Plants were subjected to a cold acclimation period of 2°C for 14 d and a sub-zero acclimation period of -2°C for 14 d in a controlled-environment chamber.  Following sub-zero acclimation, plants were exposed to simulated warming events that consisted of temperatures of 4, 8, or 12 °C for 1 or 5 d, for a total of 6 temperature-duration combinations. Freezing tolerance (lethal temperature for 50% of population, LT₅₀) was determined following each deacclimation treatment.  Overall, creeping bentgrass exhibited higher freezing tolerance (LT₅₀ of -19.2°C) in comparison to annual bluegrass (LT₅₀ of -14.3°C).  In general, annual bluegrass exhibited a loss of freezing tolerance at lower temperatures compared to creeping bentgrass.