The Distribution of "Calcicole" and "Calcifuge" Species in Relation to the Content of the Soil in Calcium Carbonate and Exchangeable Calcium, and to Soil Reaction

Abstract

CALCICOLOUS plants, or calcicoles, are commonly defined as plants found growing in soils rich in calcium carbonate: calcifugous plants, or calcifuges, as plants growing in soils deficient in or devoid of calcium carbonate, and at the same time acid in reaction. Little or no notice seems to have so far been taken of the fact that markedly plants (i.e. plants which are characteristically luxuriant on highly calcareous soils), such as Mercurialis perennis and Arum maculatum, can and very often do flourish in soils in which there is no detectable amount of calcium carbonate. The question then arises as to whether reaction alone is the determining factor, and if so what agent is responsible for preventing the normal rise of acidity of the soil with time. Determinations were made of the calcium carbonate content, exchangeable calcium content, and soil reaction of various soils in which these and other plants were growing. Estimations of nitrates were also carried out, for two purposes: first, to see whether the nitrate content in any way affected the nature of the plant growth, and secondly, whether production of nitrates, i.e. the activity of the nitrifying bacteria themselves, can be correlated with any of the other factors considered. Nitrifying bacteria generally flourish in soils that are not, or are only slightly, acid, and which usually contain calcium carbonate. The nitrifying bacteria as a group are in fact usually themselves calcicolous plants. But a number of instances are known where nitrifying bacteria are found to be quite active in acid soils. Investigation was therefore made to see whether abundance of exchangeable calcium was in any way responsible for their activity in acid soils.