We compared the use of phosphorus (P) and nitrogen (N) in slow-growing Banksia attenuata (Proteaceae), which resprouts after fire and naturally occurs on deep sand, with faster-growing opportunistic B. sessilis, which is killed by fire and occurs on shallow sand over laterite or limestone. We carried out pot experiments with plants on substrates with different P availability. We measured foliar nutrient concentrations, and P allocated to major biochemical fractions. The two species had similar foliar total P concentrations, but distinct patterns of P allocation to P-containing fractions. The foliar total N concentration of B. sessilis was greater than that of B. attenuata on all substrates. The foliar total P and N concentrations in both species decreased with decreasing P availability. The relative growth rate of both species was positively correlated with both foliar nucleic acid P and total N concentrations, but there was no correlation with other P and N fractions. Faster-growing B. sessilis allocated more P to nucleic acids than B. attenuata did, but other fractions were similar. We conclude that the nutrient-allocation patterns in faster-growing opportunistic B. sessilis and slower-growing B. attenuata revealed different strategies in response to soil P availability, which matched their contrasting growth strategy.

Under very high phosphorus (P) supply, Ptilotus hyperaccumulates P without toxicity while Kennedia is intolerant. What physiological mechanisms underlie this difference? P. exaltatus and K. prostrata were grown in sandy soil with low- and high-P treatments. Under high P, both species hyperaccumulated P (>20 mg g–1) in leaves, and shoot dry weight was unchanged for P. exaltatus but decreased by >50% for K. prostrata. Under high P, both species preferentially accumulated leaf P as inorganic P but P. exaltatus preferentially allocated P to mesophyll cells and stored Ca as occasional crystals in specific lower mesophyll cells separate from P, while K. prostrata preferentially allocated P to epidermal and spongy mesophyll cells and co-located P and Ca in palisade mesophyll cells. Mesophyll cellular [P] correlated positively with potassium for both species and negatively with sulfur for P. exaltatus. High P tolerance arose from P and Ca allocation to different leaf cell types, formation of Ca crystals, and enhanced K and decreased S accumulation to balance high cellular [P]. Intolerance to high P arose from the co-location of Ca and P in palisade mesophyll cells. This study advances the understanding of leaf physiological mechanisms for high P tolerance in plants.