Shifts in leaf N : P ratio during resorption reflect soil P in temperate rainforest

1. Large-scale syntheses of leaf and litter N and P concentrations have demonstrated that leaf and litter N : P ratios both decline with latitude, that litter N : P ratios are generally greater than those of fresh leaves, and that the difference between these two ratios increases towards the tropics. These patterns have been ascribed to either a direct effect of temperature on plant growth rates and leaf-level physiology, or a decline in soil P towards the tropics. We test the hypothesis that global patterns of leaf and litter N : P ratios reflect a soil-P gradient by examining leaf and litter N : P in all species from a temperate rainforest along a soil-P gradient. 2. The soil P gradient followed a toposequence of 20 plots. There was > 50-fold variation in soil total P from ridges (23-136 mg kg(-1)), through faces and terraces (32-744 mg kg(-1)), to gullies (440-1214 mg kg(-1)). 3. The N : P ratios of leaves and litter both declined as soil total P increased, and the N : P ratio of litter was greater than that of fresh leaves. The difference between litter N : P and fresh leaf N : P declined with increasing soil total P supporting the hypothesis that global patterns of N : P ratios reflect gradients of soil P. 4. Compositional turnover with soil P partly contributed to the total plant community leaf and litter nutrient concentration responses. However, consistent within-species responses pointed to a soil-based mechanism for determining responses by the total plant community. 5. Comparisons of our litter data to global data sets suggest that the vegetation was well adapted to low soil nutrient concentrations with 37% of litter N and 24% of litter P samples being below published thresholds for highly proficient nutrient resorption. 6. The range of leaf N and leaf P concentrations at our site captured a large portion of the range reported in global leaf trait data sets. 7. Highly proficient P resorption was responsible for the divergence in leaf and litter N : P ratios on P-poor soils. These results emphasize the significance of proficient nutrient resorption as an advantageous plant trait for nutrient conservation on P-poor soils.