Latitudinal Variation of Leaf Phosphorus Fractions Provides Physiological Insights Into Plant Phosphorus-Use Strategy at Large Scales

Three major hypotheses aim to explain latitudinal trends of leaf phosphorus (P) concentration: the Temperature-Plant Physiological Hypothesis (TPH), Soil-Nutrient Hypothesis (SNH) and Evergreen-Deciduous Hypothesis (EDH). However, these hypotheses only address leaf total P, preventing a deeper insight into the underlying physiological mechanisms. We extended these hypotheses to include variations in leaf P fractions with different physiological functions (extended TPH, SNH and EDH, respectively). We analysed latitudinal variation in leaf P fractions and their correlations with mean annual temperature (MAT), soil total P concentration (soil TP), and leaf habit. Leaf total P and P-fraction concentrations increased with increasing latitude in the Northern Hemisphere, with metabolic P increasing most. The concentrations of all leaf P fractions, higher in deciduous than in evergreen plants, increased with decreasing MAT and increasing soil TP. The proportion of metabolic P was higher at low MAT and in deciduous plants, while that of residual P increased with increasing soil TP. MAT had a much stronger influence than other factors on leaf P fractions, especially for their allocation proportions. Our results predominantly supported the extended TPH, but also generally supported the other two hypotheses, highlighting eco-physiological mechanisms underpinning the macroecology of plant P-use strategy.