# Potential Hypotheses Predicting Leaf Litter Nitrogen and Phosphorus Patterns at the Global Scale

## TL;DR

This study explores how climate and other factors influence nitrogen and phosphorus patterns in leaf litter globally, finding that different hypotheses work better for predicting phosphorus than nitrogen.

## Contribution

The study introduces new insights into the differing control mechanisms of leaf litter stoichiometry compared to green leaves.

## Key findings

- Litter nitrogen and N/P ratios decrease with latitude, while phosphorus increases.
- The Species Composition hypothesis best predicts litter phosphorus patterns.
- Environmental and biological factors explain over 40% of variations in litter stoichiometries.

## Abstract

Climate has shaped green leaf nitrogen (N) and phosphorus (P) patterns through its direct physiological effects (Temperature–Plant Physiology hypothesis), indirect pathways involving soil nutrients (Soil Substrate Age hypothesis), or vegetation composition (Species Composition hypothesis). However, the efficiencies of these hypotheses and the relative importance of the factors involved in predicting leaf litter N and P remain unresolved. We evaluated these hypotheses by analyzing 4657 global observations of leaf litter N and P concentrations and N/P ratios, demonstrating that litter stoichiometries diverged in plant functional types, and that litter N and N/P ratios declined with latitude, while P increased. The validity of each hypothesis in predicting latitudinal patterns of leaf litter P was confirmed, with the Species Composition hypothesis being the most effective model; however, all hypotheses failed to predict the litter N. Environmental and biological factors collectively explained over 40% of the variations in litter stoichiometries, with plant functional type, soil pH, and climatic factors being the most important drivers of litter N, P, and N/P ratio, respectively. The fundamentally different control mechanisms of litter stoichiometry patterns compared with those of green leaves challenge the idea that common hypotheses can predict biogeographic patterns across all leaf stages; thus, current litter element biogeochemical models and plant nutrition paradigms require revision.