Lamina–petiole scaling in coordination with canopy light capture in simple-leaved woody plants

Plant function relies on coordinated investment between photosynthetic tissues and structural support, yet trait-based frameworks have largely overlooked the petiole—a key integrative organ mediating leaf mechanics and light positioning. Here, we compiled a global dataset of nine petiole and lamina traits from simple-leaved plants, encompassing up to ~1000 species across broad geographic and climatic gradients, to test three hypotheses: (1) petiole size reflects optimization for structural demands (‘optimal size’); (2) trait scaling encodes environmental constraints on size (‘allometric allocation’); and (3) lamina–petiole allometric relationships are associated with canopy light absorption (‘scaling-coordinated light capture’). We found that petiole mass increases towards low latitudes, while mechanical slenderness and relative mass are elevated at higher latitudes—trends jointly driven by temperature and precipitation. Moreover, the strength of allometric scaling between lamina and petiole traits declines with latitude, indicating reduced structural coupling in low-energy systems. Importantly, the scaling exponent between lamina and petiole explained additional variation in the fraction of absorbed photosynthetically active radiation beyond broad climatic covariates. Synthesis. Our findings reveal that petiole traits play an important role in linking organ-level allocation strategies with ecosystem-level function. Integrating both trait coordination and growth scaling into plant functional frameworks is essential for predicting ecological responses under global environmental change.