Leaf phosphorus fractions vary with leaf economic traits among 35 Australian woody species.

Adaptations of plants to phosphorus (P) deficiency include reduced investment of leaf P in storage (orthophosphates in vacuoles), nucleic acids and membrane lipids. Yet, it is unclear how these adaptations are associated with plant ecological strategies. Five leaf P fractions (orthophosphate P, Pi ; metabolite P, PM ; nucleic acid P, PN ; lipid P, PL ; and residual P, PR ) were analysed alongside leaf economic traits among 35 Australian woody species from three habitats: one a high-P basalt-derived soil and two low-P sandstone-derived soils, one undisturbed and one disturbed by human activities with artificial P inputs. Species at the undisturbed low-P site generally exhibited lower concentrations of total leaf P ([Ptotal ]), primarily associated with lower concentrations of Pi , and PN . The relative allocation of P to each fraction varied little among sites, except that higher PL per [Ptotal ] (rPL ) was recorded at the undisturbed low-P site than at the high-P site. This higher rPL , reflecting relative allocation to membranes, was primarily associated with lower concentrations of leaf nitrogen at the undisturbed low-P site than at the high-P site. Associations between leaf P fractions and leaf nitrogen may provide a basis for understanding the variation in plant ecological strategies dependent on soil P availability.

Phosphorus and nitrogen resorption from different chemical fractions in senescing leaves of tropical tree species on Mount Kinabalu, Borneo.

Nutrient resorption, a process by which plants degrade organic compounds and resorb their nutrients from senescing tissues, is a crucial plant function to increase growth and fitness in nutrient-poor environments. Tropical trees on phosphorus (P)-poor soils are particularly known to have high P-resorption efficiency (PRE, the percentage of P resorbed from senescing leaves before abscission per total P in green leaves). However, the biochemical mechanisms underlying this greater PRE remain unclear. In this study, we determined the P concentration in easily soluble, nucleic acid, lipid and residual fractions for green and senescent leaves of 22 tree species from three sites, which differed in P availability, on the lower flanks of Mt. Kinabalu, Borneo. PRE varied from 24 to 93% and was higher in species from the P-poor site. P-resorption rate was greatest from the lipid fraction, the nucleic acid fraction, and lowest in the easily soluble fraction and the residual fraction when all the species were pooled. For species with higher PRE, P-resorption rate of the residual fraction was relatively high and was comparable in magnitude to that of the other labile fractions. This suggests that tree species inhabiting P-poor environments increased PRE by improving the degradation of recalcitrant compounds. This study suggests that plants selectively degrade organic compounds depending on environmental conditions, which is a key mechanism underlying the variation of PRE.