Evidence For Root Contraction In White Clover (Trifolium repens L.)

White clover (Trifolium repens L.) stolons become buried inthe field. It was observed that this also occurred in the greenhousewhere the accepted mechanisms of burial, treading by livestockand earthworm casting, did not occur. It was also observed thatthe crown of seedling T. repens plants become closely appressedto the soil. Experiments showed that, regardless of varietyof T. repens or depth of planting, all seedling hypocotyls firstlift the cotyledons clear of the soil, then ‘ contract’towards the soil until the cotyledons are in contact with orbelow the soil surface. Auxanometers were used to measure therate and extent of this contraction and were also attached tostolon nodes in experiments which showed that stolons move downwardsrelative to the soil surface and that the speed and extent ofthis duration varied with soil type. A further experiment showedthat only rooted nodes show this behaviour. The force exertedby the contraction of nodal roots was estimated experimentallyas 0.21 N g^-1fresh root. A mechanism for the root contraction,based on examination of root anatomy of seedling tap-roots andnodal roots, is suggested. These experiments provide evidencefor root contraction in T. repens which may lead to stolon burial.The importance of this to T. repens as a pasture species andas a means of further improving T. repens varieties is discussed.Copyright 1999 Annals of Botany Company White clover, Trifolium repens, L., stolon, seedling, burial, root, nodes, nodal, force, contractile, soil resistance, pasture, phloem, fibres.