Does calcium-enhanced phosphorus toxicity explain the absence of most Proteaceae species from calcareous habitats?

The plant family Proteaceae represents an ecologically important component of the Australian flora, contributing towards south­ western Australia's exceptionally high biodiversity. Most Proteaceae are absent from young calcareous soils, higher in soil calcium (Ca) and phosphorus (P). This study shows that Ca-enhanced P toxicity can explain the exclusion of most Proteaceae from calcareous habitats. It is proposed that Ca enhances P toxicity in Proteaceae by increasing the preferential allocation of
P to specific photosynthetic mesophyll cells, reducing physiological zinc concentrations. This thesis presents the first model describing Ca-enhanced P toxicity and highlights its importance in the distribution of Proteaceae.