Lianas (woody vines) are an abundant and diverse polyphyletic group of plants that contribute substantially to the floristic, structural, and functional diversity of tropical forests. Lianas compete intensely with trees and exhibit peak abundance in tropical forests with strong seasonal droughts. However, it remains unclear how lianas respond physiologically to seasonal drought in tropical forests and whether lianas have a dry season advantage over co-occurring trees in terms of water use and whole-plant physiology.
Dr. CHEN Yajun of Xishuangbanna Tropical Botanical Garden (XTBG) of Chinese Academy of Sciences and his teachers conducted a research in liana-rich Xishuangbanna to test the water-use depth in lianas and other trees across forests that differ in water availability. The specific goals of the study were to qualify the spatial partitioning of soil water use for lianas and cooccurring trees in the dry and wet seasons among sites, determine the seasonal changes in leaf physiological performance for lianas and trees, and characterize the regulation of whole-plant water use.
The researchers selected three primary tropical forests (karst forest, tropical seasonal forest, and flood plain forest) that differed in their dry season soil water status and established a 20 m x 30 m study plot in each forest. They measured the depth of water acquisition from the soil, as well as the sap flow and leaf eco-physiological traits for 99 individuals of 15 lianas and 34 co-occurring tree species from three forests during the dry and wet seasons.
The study showed that both lianas and trees in the dry season switched to uptake water from deep soil layers in forests with severe seasonal soil water deficits. However, lianas were able to utilize a higher proportion of deep soil water than co-occurring trees. Lianas exhibited strong stomatal control to maximize carbon fixation while minimize dry season water loss, which could reduce water loss and maintain better leaf water status under extreme water deficit (in karst forest). In addition, lianas had a much higher maximum photosynthetic rates and sap flux density in the wet season and a lower proportional decline in photosynthesis in the dry season compared with those of trees.These proved the hypothesis that lianas would use more water from the deep soil layer and thus maintain better water status and ecophysiological performance than trees during the dry season.
The results suggested that lianas are adapted to seasonal water deficit and thus the increase in drought conditions may explain increasing liana abundance in tropical forests.
The study entitled “Water-use advantage for lianas over trees in tropical seasonal forests” has been published online in New Phytologist.
