Bimodal pattern of allometric scaling along grapevine shoots

Each branch internode, with the organs growing on it, can be seen as a single morphological phytomer subunit made of structurally and functionally interrelated components. However, allometric relationships between the anatomy and morphology of these subunits remain unclear, particularly in the axial context. The aim of this study was to address this knowledge gap by measuring morpho-anatomical parameters and their allometric relationships along grapevine shoots.

To facilitate comparison, shoot length was normalized, and a relative position index was calculated for each internode, ranging from zero at the base to one at the apex. Scaling relationships between morpho-anatomical parameters along the axis were developed and validated by statistical modelling.

Most morpho-anatomical parameters displayed an axial behaviour of increasing then decreasing in size from base to apex, with the exception of shoot diameter and shoot vessel density. A relative position index of 0.2 acted as the data turning point for most variables analysed. During the first phase (relative position index of <0.2), the traits of the phytomer organs are uncoupled and show weak allometric correlation, and during the second phase the traits exhibit strong allometric relationships.

Our findings suggest that allometric relationships along grapevine shoots are not constant; they exhibit a bimodal pattern, possibly influenced by seasonal temperatures. This work could aid in managing productivity shifts in agricultural and natural systems under global climate change and adds to basic knowledge of differentiation and development of growth units in plants.