The Effect of Temperature on Cold and Heat Resistance of Growing Plants: II. COLD RESISTANT SPECIES

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Abstract
The dynamics of cold and heat resistance in a number of cold resistant plant species (potato, meadow fescue, spring and winter wheat) exposed to temperatures from −13 °C to + 50°C has been studied under controlled environmental conditions. The thermo-resistance of leaves was shown to be constant at certain temperatures (a range of background temperatures), but it increased (ranges of heat and cold hardening) or decreased (ranges of heat and cold injury) at other temperatures. A gradation of temperatures with respect of ‘thermo-resistance’ for these ranges is being proposed. The limits of the ranges vary depending on endogenous (species characteristics, phase of development) and exogenous factors (environmental conditions). Thus, at gradually rising or falling temperatures the boundaries between the ranges of hardening and injury are markedly shifted towards more extreme temperatures. Generally, the data show uniformity of responses to extreme temperatures by cold resistant plants; the differences observed between species are quantitative.