Petioles Occupy a Partly Distinct Functional Spectrum From Laminae in Broadleaved Woody Plants

The global spectrum of plant form and function has advanced our understanding of ecological strategies, yet the role of petioles has been largely overlooked. Using 7 petiole and 6 lamina traits from 304 broadleaved woody species (2060 individuals) spanning a 4000-km transect in China, we examined the composition of petiole functional structure and its integrated trait space patterns with laminae. Petiole traits define a distinct two-dimensional functional space, structured by orthogonal axes of structural investment and hydraulic efficiency. This space is independent from, and expands beyond, the lamina economics spectrum. Temperature emerges as the dominant driver of petiole structural design and hydraulic efficiency. These findings reveal petiole as a major, independent axis of functional diversity, challenging the lamina-centric paradigm and highlighting its critical role in plant adaptation to environmental heterogeneity.