Observations on Environmental and Genotypic Influences on the Overwintering of White Clover

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Abstract
Measurements were made during the winter of 1977/1978 at the Welsh Plant Breeding Station [UK] of changes of leaf, stolon and root biomass, stolon length, and reserve carbohydrate of the white clover cultivars S.100, S.184, Menna and Olwen. These cultivars were grown in the establishment year under contrasting cutting frequencies and N levels. All components of biomass declined during winter. The marked decline of leaf weight between Dec. and Feb. was probably in part due to predation by wood pigeons. Low temperature damage caused a marked reduction of stolon weight between Feb. and April. The decline of biomass was greater for infrequently cut and N fertilized treatments. Similar changes were recorded for stolon length, stolon weight per unit length and water-soluble carbohydrate content. Differences due to clover cultivars were large. The characteristics of "S.184" allowed it to overwinter and enter spring with more stolon and leaf than the other cultivars. "Olwen" showed some increase of stolon biomass by late season growth but declined markedly in late winter. Early spring growth was positively related to the weight of stolon which overwintered. Stolon CO2 fixation at 130 W/m2 exceeded stolon respiratory requirements. Daily levels of incoming radiation and temperatures above 5.degree. C would have placed clover plants below the compensation point for most of the days in Dec. Stolons developed under frequent cutting had higher net CO2 fixation. Genotypic differences and management effects on the function of the stolon as a photosynthetic or storage organ during winter are important factors determining the survival and production of white clover in Britain.