Changes in Carbohydrate and Nitrogen Metabolism Associated with Cold Deacclimation of Annual Bluegrass and Creeping Bentgrass.

Warming periods during winter and early spring months can result in premature cold deacclimation of turfgrasses and may contribute to enhanced freezing injury.  Previous research has shown that annual bluegrass (Poa annua L.) (AB) can exhibit greater sensitivity to cold deacclimation compared to creeping bentgrass (Agrostis stolonifera L.) (CB); however, the physiological mechanisms associated with interspecific differences in deacclimation capacities are unknown.  Therefore, this study was conducted to compare metabolic changes of ‘L-93’ CB, a freezing-tolerant ecotype of AB (AB-T), and a freezing-sensitive ecotype of AB (AB-S) during cold deacclimation.  Following a cold acclimation period (2 °C and -2 °C), plants were exposed to 8°C for 0.5, 1, 3, and 5 d to induce deacclimation.  Whole plants were sampled for freezing tolerance determination (lethal temperature for 50% of population, LT₅₀), and crowns were extracted for quantification of soluble sugars, amino acids, and soluble protein content.  Among the total soluble protein content, changes in dehydrin proteins were also quantified.  Cold acclimation resulted in an increase in freezing tolerance, total mono- and disaccharides, high molecular weight fructans, total amino acids, and total soluble proteins. There was a decline in the content of some specific compounds when plants were exposed to deacclimation, but responses varied depending on plant species and ecotype, as well as duration of deacclimation treatment.