Cold hardening of plants is a result of maintenance of an increased photosynthesis/respiration ratio at low temperatures

The capacity of plants for hibernation is ensured by the presence of significant food resources, like in hibernating mammals. In plants, these resources are accumulated in autumn due to maintenance of the rates of true CO2 assimilation elevated with reference to the dark respiration. This becomes possible as a result of higher thermoresistance of photosynthesis, as compared to respiration, and low light requirements for photosynthesis saturation at low positive or negative temperatures.