Adaptation to winter stress in nine white clover populations: Changes in non-structural carbohydrates during exposure to simulated winter conditions and 'spring' regrowth potential

Nine white clover populations: Grasslands Huia (H0, New Zealand), AberHerald (AH0, bred in the UK from material of Swiss origin) and Sandra (S0, Sweden); sub-populations of these (survival populations) collected after exposure to two (H2 and AH2) and four (H4, AH4 and S4) years of winter stress, respectively, at Uppsala (59 degrees 49'N, 17 degrees 39'E) and a wild ecotype (WE) from the area were subjected to two simulated winter environments (+2 degreesC, no light (W1) and [+2/-2 degreesC, 4 h photoperiod (W2) for 3 weeks] after hardening. After hardening, concentrations of total non-structural carbohydrates (TNC) differed little among the populations. However. the changes in these carbohydrates during the winter treatments differed between genetic backgrounds and populations selected for winter survival. Populations S0, S4 and WE showed lower reductions of TNC at low constant temperatures compared with H and AH populations. These populations were also able to maintain the TNC concentration in both stolons and roots despite frequent exposure to sub-lethal frosts, whereas H populations and AH0 and AH2 lost both starch and water soluble carbohydrates from the stolons in treatment W2, The ability to cope with frequent sub-lethal frosts thus appears to play a crucial role in adaptation to northern climates. There appears to have been sufficient genetic variation in AH0 for selection for this trait in the field. The amount of biomass accumulated and the rate of node production during regrowth were generally greatest after treatment W2, when the plants tended to have the highest concentrations of TNC. (C) 2001 Annals of Botany Company.