Asymmetry in leaf phosphorus concentration of woody plants and its divergent drivers in the Northern and Southern Hemispheres

Leaf phosphorus (P) concentration has traditionally been assumed to increase from the equator to the poles. However, whether there exists a uniform or symmetrical latitudinal pattern across both hemispheres has never been examined due to variation in the geological histories, land-sea distribution, and climate of the hemispheres. We analyzed global latitudinal trends in woody plant leaf P concentrations across hemispheres to evaluate four hypotheses underlying these patterns. We show that leaf P concentration was significantly higher in the Northern Hemisphere than in the Southern Hemisphere, increasing with latitude in the former but decreasing in the latter. Key drivers of leaf P concentration differed between hemispheres: temperature dominated Northern Hemisphere variations, supporting the Temperature-Plant Physiology Hypothesis, while soil available P (indicative of substrate age) primarily influenced Southern Hemisphere trends, supporting the Soil Substrate Age Hypothesis. Temperature and precipitation play opposite roles in forming the leaf P latitudinal patterns in the two hemispheres. Our findings challenge the notion of a traditional latitudinal P gradient and emphasize incorporating hemisphere-specific climatic and edaphic drivers into forest productivity and global P-cycling models. Resolving these asymmetries will improve predictions of vegetation responses to environmental change and enhance Earth system model accuracy.