THE EFFECT OF SOIL-WATER POTENTIAL ON SEEDLING GROWTH OF SOME BRITISH PLANTS

Seedlings of 15 species from a range of habitats contrasting in soil water status were grown at known soil water matric potentials ranging from near field capacity to the permanent wilting potential (-0.05, -0.5, -1.0 and -1.5 MPa). Root and shoot growth were differentially very sensitive to soil water matric potential: root growth continued at lower soil water matric potentials than shoot growth. All species from drier habitats established better in drier soils than wetland species, with increased root growth in drier soils in contrast to decreased root growth of wetland species in drier soils. Seed size was thought to be an important factor in determining establishment in dry soils; the only wetland species to maintain substantial root growth in dry soils had comparatively large seeds. The seedling growth responses were compared with the same species' germination responses in relation to the above range of soil water matric potentials (established in a previous study). Sensitivity to soil moisture may occur at the germination or seedling stage of growth.