Variation in leaf vein traits of Pinaceae plants on the eastern Qinghai-Tibet Plateau, China.

To explore the adaptative strategies of single-veined plants along the environmental gradient, we collec-ted leaves of 57 Pinaceae species (including , and ) from 48 sites along a latitudinal gradient (26°58'-35°33' N) on the eastern Qinghai-Tibet Plateau. By measuring three traits of leaf vein, including vein length per leaf area, vein diameter, and vein volume per unit leaf volume, we analyzed the trade-off between vein traits and their relationship with environmental changes. The results showed no significant difference in vein length per leaf area among different genera, but significant difference in vein diameter and vein volume per unit leaf volume. There was a positive correlation between vein diameter and vein volume per unit leaf volume for all genera. There was no significant correlation of vein length per leaf area with vein diameter and vein volume per unit leaf volume. With the increases of latitude, vein diameter and vein volume per unit leaf volume significantly decreased. In contrast, vein length per leaf area did not show a latitudinal trend. Mean annual temperature was the main factor driving the variation in vein diameter and vein volume per unit leaf volume. The relationships between vein length per leaf area and environmental factors were relatively weak. These results indicated that the single-veined Pinaceae plants have a special adaptative strategy to environmental changes through adjusting vein diameter and vein volume per unit leaf volume, which is quite different from complex vein structures such as reticular veins.