Abstract:

In this study, we measured the branch xylem structure of 85 woody plant species at the Shanghai Chenshan Botanical Garden to compare vessel characteristics among different life forms and check their phylogenetic signals. The trade-off between vessel density and vessel size was subsequently compared among different life forms. The results showed that: ① The vessel diameter ((28.55 ± 8.84) μm) and vessel ratio (8.7% ± 2.89%) of evergreen woody plants were significantly smaller than the vessel diameter ((35.81 ± 13.92) μm) and vessel ratio (12.7% ± 4.82%) of deciduous woody plants; meanwhile, there was no significant difference observed in the vessel density between evergreen plants ((149.3 ± 75.62) N/mm²) and deciduous plants ((164.5 ± 154.28) N/mm²). The vessel diameter of trees ((35.86 ± 13.5) μm) was significantly larger than that of shrubs ((26.24 ± 8.84) μm), but there was no significant difference observed in the vessel ratio and vessel density between trees (12.09% ± 5.01%; (151.9 ± 142.73) N/mm²) and shrubs (10.59% ± 2.99%; (208.7 ± 126.37) N/mm²). ② There were significant phylogenetic signals observed in vessel diameter and vessel density, and the signal of vessel density was larger than that of vessel diameter. There was, however, no obvious phylogenetic signal in the vessel ratio. ③ The standardized major axis test indicated that the trade-off between vessel density and vessel size existed in all life forms, with a common slope coefficient of –0.89 and a 95% confidence interval (–0.98 ~ –0.79). However, the intercept of evergreen trees was significantly smaller than that of deciduous trees, suggesting that deciduous trees have a larger vessel diameter than evergreen trees for a given vessel density.

Key words: plant functional traits, vessel traits, life form, density-size trade-offs, phylogeny