Biogeography of community canopy leaf traits and their links to global forest photosynthesis

Leaf traits influence biotic interactions and ecosystem functions in forests. However, biogeographic drivers of leaf traits remain highly uncertain, limiting their integration into global vegetation models. Using a global dataset of forest plots, we show that community canopy leaf traits align along three dimensions: leaf economy, leaf density, and nitrogen-to-phosphorus (N:P) ratio. Changes in these trait dimensions across forest communities were driven by different variables: leaf economy was primarily shaped by the proportion of deciduous trees, leaf density by soil available P and temperature, and leaf N:P ratio by temperature. These three leaf trait dimensions together explained 60.2% of the variation in ecosystem-scale forest maximum photosynthesis, with the leaf N:P ratio showing the strongest association, followed by the dimensions of leaf economy and leaf density. Forests with moderate leaf N:P ratios and more acquisitive traits had higher photosynthesis than other forests. Our findings highlight the potential of community canopy leaf traits in predicting biogeographic variation in ecosystem-scale forest functioning.