The determination of plant vessel structure is fundamental for further understanding vascular function in different plant groups. Vessel dimorphism may be an important hydraulic strategy and ecological adaptation of plants. Previous studies have found that lianas, a common tropical and subtropical plant growth form, generally have larger vessel diameters than co-occurring trees. However, these results may differ among vegetation types.
In a study published in American Journal of Botany, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences developed a theoretical model to predict how vessel diameters vary between lianas and trees and across sites (Xishuangbanna tropical seasonal rainforest, Yuanjiang savanna and Ailaoshan subtropical evergreen broadleaf forest in Yunnan).
The researchers evaluated variation in liana and tree vessel diameter distributions and six xylem hydraulic traits (mean vessel diameter, hydraulically weighted vessel diameter, vessel density, theoretical hydraulic conductivity, vessel area fraction, and sapwood density).
They found that lianas had greater vessel diameter, vessel area fraction, dimorphism, theoretical hydraulic conductivity, and lower sapwood density than trees. Furthermore, these differences were consistent across contrasting forest types.
In contrast, they found that trees had consistently conservative hydraulic traits, with relatively small vessel diameter and low vessel dimorphism due to the lack of large vessels. The difference in liana and tree hydraulic traits may explain why lianas and trees tend to have different distributions and relative abundances in tropical environments.
"Our results suggest that lianas have large vessels, even in dry and cold habitats," said Prof. ZHNAG Jiaolin of XTBG.
According to the researchers, a dimorphic vessel pattern may allow lianas to grow well when water is available and also to reduce their risk of embolism when water becomes limiting, ensuring both high hydraulic efficiency and safety, which may contribute significantly to the occurrence and survival of lianas in seasonal, dry, cold habitats.
