Freezing Tolerance and Carbohydrate Changes during Cold Acclimation of Green‐Type Annual Bluegrass (Poa annua L.) Ecotypes

Abstract

Winterkill is recurrently observed on annual bluegrass (Poa annua L.) golf greens in northern climates. Although annual bluegrass susceptibility to freezing temperatures has been pointed out as a major factor responsible for winter damages, little information exists on freezing tolerance and cold hardening of green‐type annual bluegrass. This study was conducted to assess freezing tolerance and carbohydrate changes occurring during cold acclimation of green‐type annual bluegrass ecotypes cold hardened under both environmentally controlled and simulated winter conditions in an unheated greenhouse. The 50% killing temperatures (LT50), levels of fructans, and mono and disaccharides were determined during cold acclimation in three annual bluegrass ecotypes originating from Western Pennsylvania (OK), Coastal Maryland (CO) and Central Québec (CR). The ecotypes differed significantly with regard to their freezing tolerance (LT50 ranking: OK < CO < CR) and maintained their relative ranking under both environmentally controlled and simulated‐natural winter conditions. Maximum freezing tolerance was observed after exposure to nonlethal subfreezing temperatures and annual bluegrass achieved high levels of freezing tolerance with LT50 of −31.2°C for OK, −24.6°C for CO, and −22.8°C for CR. High molecular weight fructans (DP>6) were the most abundant carbohydrates found in plants cold‐acclimated under low, nonfreezing temperature with levels up to 170 mg g−1 dry weight as compared with 60 to 70 mg g−1 dry weight in nonacclimated plants. Sucrose levels in crowns of annual bluegrass markedly increased at temperatures below freezing and maximum sucrose concentration coincided with maximum freezing tolerance of annual bluegrass. However, variations in fructan and sucrose levels were not related to differential freezing tolerance among the three annual bluegrass ecotypes tested.

Comparative assessment of metabolic responses to cold acclimation and deacclimation in annual bluegrass and creeping bentgrass

“…In the current study, exposure to 2 • C induced only a moderate increase in freezing tolerance whereas subsequent incubation at −2 • C caused a surge in freezing tolerance and unambiguous differentiation of species/ecotypes with regard to cold hardiness potential. Enhancement of freezing tolerance after acclimation at a non-lethal subzero temperature has been documented in many plant species (Castonguay et al, 1995;Herman et al, 2006;Livingston et al, 2007) including AB (Dionne et al, 2001a). Our results confirm previous observations that CB is more freezing tolerant than AB under field (Tompkins et al, 2000) and controlled (Tompkins et al, 2004;Hoffman et al, 2014) conditions following cold acclimation.…”

“…At 20 and 2 • C, plants were maintained under a 10 h photoperiod and PPFD of 300 mol m −2 s −1 and plants subjected to subzero acclimation were maintained in the dark. This temperature regime was previously determined to induce cold acclimation in AB and other cool-season turfgrass species (Dionne et al, 2001a;Hoffman et al, 2010). Deacclimation was initiated after the completion of the 4-wk cold acclimation period and consisted of the following six treatments:…”

“…Plants subjected to −2 • C for 2 wk were thawed for 12 h at 2 • C to facilitate sampling as described by Dionne et al (2001a). Whole plants were obtained for freezing tolerance determination and individual crowns were harvested (1 cm above and below the transition zone between shoot and root) for biochemical analyses.…”

“…AB ecotypes with contrasting tolerance to freezing temperatures have been previously identified (Dionne et al, 2001a). Recently, Dionne et al (2010) documented a wide range of variability in freezing tolerance among AB ecotypes from diverse origins.…”

Optimal Regulation of the Balance between Productivity and Overwintering of Perennial Grasses in a Warmer Climate

“…In temperate perennial grasses, simple carbohydrates accumulate during cold acclimation and most of these are converted into fructans, which accumulate mainly in the basal part of the shoot [18,62,63]. In regions with a long winter, a storage of organic reserves, particularly carbohydrates, are necessary for maintenance respiration, stress responses, and early spring regrowth.…”