Effects of adaptation to winter stress on biomass production, growth and morphology of three contrasting white clover cultivars

Changes in biomass production and partitioning, together with morphology an d growth of three white clover (Trifolium repens L.) cultivars after exposu re to winter stress were recorded in a controlled environment study. The cu ltivars used were Grasslands Huia (H. New Zealand), AberHerald (AH. bred in UK from material of Swiss origin) and Sandra (S, Sweden), sub-populations of these (survival populations), and a wild ecotype from the Uppsala area. The sub-populations Here collected after 2 (with the exception of S) and 4 years of winter stress, respectively, at Uppsala (59 degrees 49' N, 17 degr ees 39' E). In the controlled environment study the photoperiod was 12 h an d there were two temperature regimes, namely 23/18 and 12/9 degrees C (day/ night), respectively. The experimental plants were cloned from eight differ ent plants of each population. There were few interactions between populati ons and temperature regimes. Biomass production was lowest in the Swedish p opulations and in the surviving populations of the other cultivars collecte d after 4 years of exposure to winter stress. However, biomass partitioning , with the exception of allocation to branches, remained unaffected. Morpho logy differed significantly between cultivars, but, with the exception of i nternode length, was unaffected by exposure to winter stress. Internode len gth, was significantly reduced in surviving populations of both H and AH af ter exposure to four winters, when its value was similar to that of the Swe dish populations. The reduced internode length was a result of a greater re duction in the stolen extension rate than in the leaf appearance rate of su rvival populations compared with the original populations. It is hypothesis ed that reduced internode length would hale implications for the carbon eco nomy of the plant.