Some mineral relations of plants and soils

Abstract

The following papers record an investigation of some relations between vegetation and the soil in three major types of habitat - (1) Lake District woodland on non-calcareous glacial drift, (2) aquatic and waterlogged sites in the same region, and (3) an upland granitic area in Scotland. An attempt has been made to relate certain properties of the soil exchange complex to processes of soil development, and to vegetational differentiation and nutrient status. The major conclusions drawn may be summarized as follows: (1) In the woodlands studied, topography appears to be the main factor in determining whether a flushed brown earth with a mull humus layer and an ash-sycamore-oak-hazel tree community will develop, or a leached podzolic brown earth with a more humus layer and oak, birch and rowan as the characteristic trees. (2) In passing; from relatively inorganic underwater soils - through marsh, fen and lacustrine bog, soils - to highly organic raised bog peats; both the amount and strength of soil acids increase, C/N ratio rises, and base saturation falls. This is reflected in the nutrient status of the plants; those from underwater habitats being highest in minerals and nitrogen, and those from raised bogs being loci in both these constituents. (3) It appears that the first addition of organic matter to the Scottish granitic soils brings about a sharp increase in acidity and a marked fall in base saturation. The presence of comparatively strong acids in the humus produced by the colonizing plants is suggested as a possible advantage, in view of the difficulty of obtaining mineral nutrients from the c smite substratum. A study has also been made of some elements and chemical properties figuring in the exchange complex of a peat profile (Journal of Ecology, 1949). Some of the variations may well be related to those in the vegetational composition of the peats, for a sequence of plant communities of very different character has occupied the site as distance from the mineral soil has increased. Conjointly with A. M. Mayer an investigation of iron and manganese in natural vegetation of the Lake District has been carried out (Annals of Botany, 1951). The content of both elements is higher in natural vegetation than is usual in crop plants, probably because of the greater acidity and organic content of the natural soils. The amounts absorbed are shown to vary with the species, the plant group, and the habitat.