Comparing Carbon Metabolism of Creeping Bentgrass and Annual Bluegrass During Cold Deacclimation.

Premature losses in freezing tolerance and winter injury of some cool-season turfgrasses can be a problem in northern climates.  In order to reduce the economic losses and maintenance costs associated with premature deacclimation, a better understanding of the underlying physiological factors that contribute to turfgrass freezing tolerance is needed. Therefore, the objectives of this study were to: (1) compare the freezing tolerance of annual bluegrass (Poa annua L.) (AB) and creeping bentgrass (Agrostis stolonifera L.) (CB) during deacclimation; (2) examine changes in carbon metabolism for these two species during deacclimation. Plants were maintained in the greenhouse for 3 months and then moved to the growth chamber for cold acclimation and deacclimation. Plants were exposed to 5 treatment temperatures including: (1) non-acclimated control at 20 °C; (2) cold acclimated at 2 °C; (3) cold acclimated at -2 °C; (4) deacclimated at 8 °C for 1 d; and (5) deacclimated at 8 °C for 5 d. At the end of each treatment, changes in freezing tolerance were determined based on lethal temperature resulting in 50% kill (LT50).  In addition, carbon metabolic activities including photosynthesis, respiration, and chlorophyll fluorescence parameters, including photochemical efficiency (Fv/Fm) and photochemical yield (Yield), were measured following each treatment. Overall, CB exhibited higher freezing tolerance (lower LT₅₀) following cold acclimation, and also maintained higher freezing tolerance during deacclimation compared to AB, as demonstrated by a lower LT₅₀ at 8 °C for 1 and 5 d. Photosynthesis, respiration, Fv/Fm and Yield of AB increased more rapidly during deacclimation, which suggested that the metabolic and physiological activities of AB are activated earlier in response to temperature increases. This may be an important factor explaining differences in winter injury susceptibility between AB and CB.