Stable stomatal number per minor vein length indicates the coordination between leaf water supply and demand in three leguminous species

The coordination between minor vein density (MVD) and stomatal density (SD) has been found in many plants. However, we still know little about the influence of leaf node on this correlation relationship. Here, we devised the new functional trait ‘stomatal number per minor vein length’ (SV). By measuring leaflet area (LA), MVD, SD, and SV, we demonstrated the significance of this functional trait in Arachis hypogaea (peanut) grown under different light regimes and in sun leaves of Dalbergia odorifera and Desmodium renifolium. We found that SV did not change significantly with leaflet node or with LA within each light treatment, while shading caused a significant decrease in SV. The positive correlation between SD and MVD was found in peanut under each light regime. Sun leaves of D. odorifera and D. renifolium also had stable SV along the leaflet node, with a positive correlation between MVD and SD. We conclude that under a certain light regime, a stable SV similar to the positive correlation between MVD and SD can also indicate the coordination between leaf water supply and demand. Our findings highlight the significance of SV and provide new insight into the coordination between stomatal number and minor vein length.