Calcium‐enhanced phosphorus toxicity in calcifuge and soil‐indifferent Proteaceae along the Jurien Bay chronosequence.

Summary: Many Proteaceae are highly phosphorus (P)‐sensitive and occur exclusively on old nutrient‐impoverished acidic soils (calcifuge), whilst a few also occur on young calcareous soils (soil‐indifferent) that are higher in available calcium (Ca) and P. Calcium increases the severity of P‐toxicity symptoms, but its underlying mechanisms are unknown. We propose that Ca‐enhanced P toxicity explains the calcifuge habit of most Proteaceae.Four calcifuge and four soil‐indifferent Proteaceae from South‐Western Australia were grown in hydroponics, at a range of P and Ca concentrations.Calcium increased the severity of P‐toxicity symptoms in all species. Calcifuge Proteaceae were more sensitive to Ca‐enhanced P toxicity than soil‐indifferent ones. Calcifuges shared these traits: low leaf zinc concentration ([Zn]), low Zn allocation to leaves, low leaf [Zn]:[P], low root : shoot ratio, and high seed P content, compared with soil‐indifferent species.This is the first demonstration of Ca‐enhanced P toxicity across multiple species. Calcium‐enhanced P toxicity provides an explanation for the calcifuge habit of most Proteaceae and is critical for the management of this iconic Australian family. This study represents a major advance towards an understanding of the physiological mechanisms of P toxicity and its role in the distribution of Proteaceae. [ABSTRACT FROM AUTHOR]