Relative effects of temperature vs. photoperiod on growth and cold acclimation of northern and southern ecotypes of the grass Arrhenatherum elatius

- Temperature is more important than photoperiod for cold acclimation of a grass.
- Northern ecotypes are more responsive to cold acclimation cues.
- Ecotypic cold acclimation differences in A. elatius resemble tree patterns.
- For biomass production, faster growth pre-winter outweighs frost damage effects.

Growth of perennial grasses in the fall represents a balance between an extended growing season and increased vulnerability to frost. Within species along latitudinal gradients, plants may exhibit ecotype-specific sensitivities to the temperature and photoperiod cues that influence cold acclimation. Therefore, it is unclear for a given latitude how climate warming will alter the timing and extent of cold acclimation, and thus vulnerability to frost events. We evaluated relative temperature and photoperiod sensitivities during simulated cold acclimation for two northern (Swedish) and two southern (Italian) ecotypes of the common forage grass Arrhenatherum elatius. Three temperature levels (Templow: 3 °C, Temphigh+low: 8 °C followed by 3 °C, and Temphigh: 8 °C) were crossed with 2 photoperiod levels (Photoshort: 6 h, and Photolong: 12 h) and administered to the plants for a three week acclimation period. All plants were then frozen at −8 °C for 1 d, and post-frost growth was measured after 3 weeks. Temphigh and Photolong increased growth prior to frost, but resulted in decreased growth after frost. The effects of temperature on sugar concentration, biomass and flower presence depended on photoperiod, with temperature only influencing sugar concentration and flowering at Photoshort, while Photolong increased biomass only at the high temperature. The faster growth rate of southern A. elatius ecotypes before frost, in combination with sufficient cold acclimation, resulted in higher biomass accumulation after frost. The faster growth habit of southern ecotypes may be advantageous in accumulating higher summer biomass even after moderate frost events in the fall.