Curvature-induced stiffening in leaf*

Water stress directly affects crop growth and is used as a key indicator in evaluating the crop yield. There were several non-destructive approaches suggested to utilize the relationship between water stress and leaf vibration frequency, but the tendency of the frequency due to the dryness was controversial. Here, we proposed a new perspective of leaf surface curvature effect to vibration frequency in order to understand this discrepancy. The change of leaf curvature due to dryness was measured through a 3D scan of individual leaves each day it underwent drought conditions. The leaves were observed to undergo two types of drying patterns. In some leaves, drought conditions led to an increase in upward transversal curvature, while in others, they wilted without significant change in surface curvature. We show that topological changes due to dryness influence the overall stiffness of the leaf and contribute to increasing the frequency when vibrating. These results indicate that the morphological feature of leaves is key to the vibration frequency.