Uptaking the P – it’s the art of the soluble
I learned much of my early botany in the south-east of England. One of my abiding memories is the abrupt floral transition between the calcareous soils of the hills known as the North and South Downs and the more acid soils of the neighbouring ecosystems. Plants which favour limestone-derived soils are known as calcicoles while those avoiding such soils are known as calcifuges. The inability of calcifuges to grow well in calcareous habitats is based on several factors, from intolerance of excess calcium and/or of alkaline pH to a disruption in iron metabolism. However, there are still aspects of calcifuge physiology that are poorly understood. One of these is the relationship between calcium accumulation and phosphorus nutrition, which has been studied by Angelika Zohlen and Germund Tyler at Lund, Sweden (pp. 427–432). They compared the growth of calcicole and calcifuge herbs and grasses in a mildly acidic non-calcareous soil and a calcareous soil; we concentrate here on the latter. Their results show clearly that growth of all the calcifuges, as measured by biomass accumulation, was markedly reduced when plants were on the calcareous soil. Chemical analysis of the plants showed that, on the calcareous soil, the calcifuge herbs had much lower concentrations of P than the calcicole herbs, suggesting an inhibition of P uptake. Further, a much smaller proportion of the total P was present as water-soluble Pi, i.e. a smaller proportion of a smaller total was available in the plant. The authors suggest that this results from a failure by the calcifuges to regulate Ca uptake from the calcareous soil, leading to the formation of Ca phosphate in the plant. However, this is clearly not the whole story because the calcifuge grasses, although exhibiting a similar growth inhibition to the herbs, suffered much less inhibition of P-uptake than the herbs and were able to maintain a much higher proportion of the P as water-soluble Pi.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
