Freezing Out Drought

Studies on the relationship between winter dormancy and drought tolerance in lucerne Lucerne cultivars can be broadly classified based on their growth response in autumn and winter into four genotypes: winter dormant, semi-winter dormant, winter active and highly winter active. These genotypic classifications are linked to the cultivars measured rate of survival when exposed to freezing temperatures. Consequently, winter dormant cultivars outperform the more winter active cultivars in terms of persistence and long term production when grown in environments that experience freezing winters. However, it is also commonly noted that in other environments where there is no exposure of the plant to sub-zero temperatures over winter, winter dormant genotypes outperform winter active genotypes. Specifically, this phenomenon has been noted in environments where water is limiting and when the stress of water deficits is alleviated through irrigation, production by winter active and highly winter active genotypes equals or exceeds that of the winter dormant and semi-winter dormant genotypes. Winter dormant genotypes when exposed to water deficit, have been observed to maintain more favourable shoot water potentials, more adaptive stomata, greater rates of photosynthesis and greater taproot starch concentrations when compared to winter active genotypes. Both freezing stress and drought stress are similar in their effect on cell function in that they both cause considerable cellular dehydration. The strategies that plants employ to adapt to both stress factors are similar and include the accumulation of small molecules (e.g. simple sugars, amino acids) in the cytoplasm to increase the cells osmotic potential and modifications to protein complexes allowing continued function during dehydration. Given the similarities between both freezing and drought stress at a cellular level and the strategies plants employ to minimise stresses on physiological