The Growth and Competitive Ability of Contrasting Natural Populations of Trifolium Repens L. on Calcareous and Acid Soils

Abstract

Trifolium repens has a wide edaphic tolerance, growing on soils ranging from highly calcareous to markedly acid (pH 4 8). Such a wide edaphic tolerance may be due either to individuals exhibiting extreme physiological homeostasis (Waddington 1957), or to the existence within the species of separate, genetically determined, physiological types, termed 'edaphic ecotypes', each adapted to a limited range of soil conditions. Although ecotypic differentiation in response to climatic factors is well documented for a number of species (McMillan 1960) there is little published evidence of such natural differentiation in response to soil factors (Snaydon & Bradshaw 1961). Several studies have, however, indicated the possible existence of variability in response to soil factors between cultivated varieties of T. repens. McNeur (1953) determined the yield of two clones of T. repens over a range of soil acidity and found that the clones responded similarly except at pH 3 7, the lowest level of pH used; further investigation (McNeur 1954) with a larger number of clones failed to confirm this difference at low pH. Robinson (1942) demonstrated differences between clones of T. repens in content of calcium, potassium and phosphate, he algo produced some evidence (unpublished) of differences between clones in yield response to lime and phosphate. Vose (1960) has also shown differences between cultivated varieties of T. repens in calcium content and in response to contrasting soils. The present investigation was designed firstly to study the possible occurrence of ecotypic differentiation between natural populations of T. repens from contrasting soil types, by comparing their performance on those soil types, and secondly to study the influence of competition between contrasting populations upon their performance on the contrasting soils. The latter aspect would seem important in view of the large influence of inter-specific competition upon the differential response of contrasting species to soil factors (Tansley 1917, Moore 1959).