# Effect of life cycle and venation pattern on the coordination between stomatal and vein densities of herbs

## TL;DR

This study explores how the life cycle and venation pattern of herbs influence the coordination between vein and stomatal densities, revealing differences in water use strategies.

## Contribution

The study identifies that vein density, not stomatal density, is more adaptable in coordinating leaf water supply and demand across different herb types.

## Key findings

- A linear correlation between total vein length per area and stomatal density was found in perennial and reticular vein herbs.
- Major vein density and minor vein diameter were significantly influenced by the interaction of life cycle and venation pattern.
- Parallel vein and annual herbs showed higher leaf area and vein diameter but lower vein density compared to reticular and perennial herbs.

## Abstract

Life cycle (annual vs perennial) and leaf venation pattern (parallel and reticular) are known to be related to water use strategies in herb species and critical adaptation to certain climatic conditions. However, the effect of these two traits and how they influence the coordination between vein density (vein length per area, VLA) and stomatal density (SD) remains unclear. In this study, we examined the leaves of 53 herb species from a subtropical botanical garden in Guangdong Province, China, including herbs with different life cycles and leaf venation patterns. We assessed 21 leaf water-related functional traits for all species, including leaf area (LA), major and minor VLA, major and minor vein diameter (VD), SD and stomatal length (SL). The results showed no significant differences in mean SD and SL between either functional group (parallel venation vs reticular venation and annual vs perennial). However, parallel vein herbs and perennial herbs displayed a significantly higher mean LA and minor VD, and lower minor VLA compared to reticular vein herbs and annual herbs, respectively. There was a linear correlation between total VLA and SD in perennial and reticular vein herbs, but this kind of correlation was not found in annual and parallel vein herbs. The major VLA and minor VD were significantly affected by the interaction between life cycle and leaf venation pattern. Our findings suggested that VLA, rather than SD, may serve as a more adaptable structure regulated by herbaceous plants to support the coordination between leaf water supply and demand in the context of different life cycles and leaf venation patterns. The results of the present study provide mechanistic understandings of functional advantages of different leaf types, which may involve in species fitness in community assembly and divergent responses to climate changes.

We examined 21 leaf water-related functional traits of 53 herb species with different life cycles and leaf venation patterns. The results showed that there was a linear correlation between total vein length per area (VLA) and stomatal density (SD) in perennial and reticular vein herbs, but this kind of correlation was not found in annual and parallel vein herbs. The major VLA and minor vein diameter were significantly affected by the interaction between life cycle and leaf venation pattern. Our findings suggested that VLA, rather than SD, may serve as a more adaptable structure regulated by herbaceous plants to support the coordination between leaf water supply and demand in the context of different life cycles and leaf venation patterns.