Reproductive traits and accumulation of nitrogen and phosphorus during the development of fruits of Protea compacta R. Br. (Calcifuge) and Protea obtusifolia Buek. ex Meisn. (Calcicole)

Abstract

Protea compacta R. Br. and P. obtusifolia Buek. ex Meisn. are closely related, non‐sprouting serotinous shrubs occurring on the Agulhas Plain, South Africa. The former grows in highly infertile acidic sands and the latter in more fertile alkaline sands. These species were used in a comparative study designed to explore the role of soil type as a selective factor in the evolution of seed size, number and nutrient content. The calcifuge P. compacta had larger seeds with higher N and P content but a lower annual seed production than the calcicole P. obtusifolia. It is proposed that P. compacta exhibits a trade‐off between seed and crop size since it requires larger, more nutritious seeds to establish in the infertile soils. In both species the accumulation of high concentrations of nitrogen and phosphorus in developing infructescenes (cones) was delayed until seed ripening. The significance of this for ecosystem losses of N and P, associated with flower and cone harvesting, are discussed. Copyright © 1989, Wiley Blackwell. All rights reserved