Seasonal Variation of Nutrient Concentrations in a Semi-Arid Savanna Ecosystem in Botswana

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Abstract
(1) Seasonal changes of nutrient concentrations in the leaves of the main tree and grass species of a semi-arid savanna in Botswana have been analysed. (2) The nitrogen concentration in the leaves of shallow-rooted Acacia species is higher than in deep-rooted ones. The higher nitrogen status of the shallow-rooted Acacia species could be the cause for their encroachment into overgrazed areas. (3) Substantial quantities of nitrogen and phosphorus are translocated from the deciduous leaves to perennial organs long before leaf abscission; sodium, calcium and iron are accumulated in older leaves. (4) A comparison of the nutrient budgets of inflorescences and infructescences in trees shows a strong nutrient demand for the developing infructescence. It is suggested that the high variability in fruit production between and within trees is caused by the high phosphorus demand of the developing fruit.