A Seedling Bioassay on Some Soils in the Sheffield Area

Abstract

The effect of soil factors on the germination and seedling establishment of potential invaders of gaps which occur across edaphic transitions was studied. Seven species, representing a range of ecological tolerance from calcicole to calcifuge, were grown on 9 soils of differing chemical and physical characteristics. Both radicle emergence and seedling survival of the calcicoles were adversely affected on the acidic soils but the calcifuge species were much less affected on the calcareous soU. Scabiosa columbaria, Urtica dioica and Erigeron acer failed on the acidic soils owing to factors which became inoperative when the pH of the soil was raised. Deschampsia flexuosa was the only calcifuge species adversely af-fected by the calcareous soils and symptoms increased with the increasing calcium carbonate content of the medium. Digitalis purpurea was the only species significantly affected by the physical nature of the soils. This effect was on rate of germination rather than on numbers germinating and was independent of soil reaction. When seed from species restricted to the calcareous side of an edaphic boundary falls on the acidic side, failure to become established during the early seedling phase is largely due to chemical soil factors. When seed from species growing on the acidic side fall on the calcareous side of the boundary, radicle emergence is not affected, but subsequent growth is slowed to a degree which depends upon the calcareousness of the soil. Elimination of these species from the calcareous sites is likely to be completed by factors other than soil chemical ones. Species most tolerant of extreme edaphic conditions were those with the lowest relative growth rates on the fertile garden soil used as a control. The 2 ruderal species Rumex acetosa and Urtica dioica had the highest relative growth rates but these were drastically reduced on the exposed field soils. There was no direct evidence that either P or K was a primary factor limiting growth in the soils tested. Principal-component analyses confirmed groupings of species and of soil characteristics noted in the field and in other experiments, and also showed the value of the method for presenting complex data.