Ecological Aspects of the Nutrition of Deschampsia Flexuosa (L.) Trin. III. Investigation of Phosphorus Requirement and Response to Aluminium in Water Culture, and a Study of Growth in Soil

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Abstract
The growth of Deschampsia flexuosa and Lolium perenne was studied in a water culture experiment in which treatments with aluminium and phosphorus were applied. The aim of the experiment was to determine whether aluminium is of benefit to the growth of established plants of Deschampsia flexuosa and whether this species has a lower requirement for phosphorus than species of less acid soils. Aluminium was provided at 0 and 4 ppm, but the various levels of phosphorus, most of which were deficiency treatments, were based not on concentration but on the total quantity expected to be absorbed by both species growing vigorously during the period of the experiment. This approach was used as an alternative to attempting to hold steady very low concentrations of phosphorus. D. flexuosa suffered less from the lowest phosphorus levels than did Lolium perenne and in shoot growth it responded to aluminium to a small but significant degree. Aluminium was toxic to L. perenne. In experiments in soil, it was shown that Deschampsia flexuosa could grow in soils of pH 5.0-6.3 from which it was excluded in the field, but that it was susceptible to plant competition. It was concluded that acid soils confer no specific nutritional benefits on D. flexuosa but are a refuge for it from competition from more vigorous but less acid-tolerant species. At the conclusion of the paper, brief discussion is given to the assumptions about plant-soil relationships which have been made in recent autecological studies of nutrition, including the present one. It is argued that certain of these assumptions, particularly that treatments can be meaningfully defined in terms of a nutrient's concentration, are as yet unjustified.