The effect of soil water potential on seed germination of some British plants.

'Seeds' of 15 species collected from a range of habitats contrasting in soil water status were germinated in soils of known matric potentials ranging from near field capacity to the permanent wilting potential (- 0.05, -0.5, -1.0 and -1.5 MPa). Germination was very sensitive to soil water potential and species responded in various ways. Some showed germination responses which correlated with the soil water status of their native habitat: none of the wetland species studied could germinate to any great extent at low soil water potentials; in contrast some species associated with drier habitats achieved high levels of germination in soils as dry as -1.0 MPa (and -1.5 MPa for one ruderal species). However, other species from drier habitats failed to germinate at low soil water potentials, and it is suggested that this may be a mechanism to avoid exposing the seedling to an unfavourable environment.