Evidence for root contraction in white clover (Trifolium repens L.)

White clover (Trifolium repens L.) stolons become buried in the field. It was observed that this also occurred in the greenhouse where the accepted mechanisms of burial, treading by livestock and earthworm casting, did not occur. It was also observed that the crown of seedling T. repens plants become closely appressed to the soil. Experiments showed that, regardless of variety of T. repens or depth of planting, all seedling hypocotyls first lift the cotyledons clear of the soil, then 'contract' towards the soil until the cotyledons are in contact with or below the soil surface. Auxanometers were used to measure the rate and extent of this contraction and were also attached to stolen nodes in experiments which showed that stolons move downwards relative to the soil surface and that the speed and extent of this duration varied with soil type. A further experiment showed that only rooted nodes show this behaviour. The force exerted by the contraction of nodal roots was estimated experimentally as 0.21 N g(-1) fresh root. A mechanism for the root contraction, based on examination of root anatomy of seedling tap-roots and nodal roots, is suggested. These experiments provide evidence for root contraction in T. repens which may lead to stolen burial. The importance of this to T. repens as a pasture species and as a means of further improving T. repens varieties is discussed. (C) 1999 Annals of Botany Company.