Resource-based explanations for species abundance and distribution remain challenging in high diversity systems such as tropical forests. Trees and lianas, two important components of tropical forests, apparently compete strongly for resources. Lianas may compete particularly well with trees during seasonal drought, since recent studies show that lianas grow most in high-light, low rainfall conditions. However, few studies have examined whether differences in resource competition between trees and lianas can be quantified using different physiological functional traits. Here, we test the hypothesis that lianas have physiological functional traits that confer greater competitive ability than those of trees, and that differences between these traits are magnified during the dry season. We measured leaf hydraulic conductance, stomatal conductance and turgor loss point in six species of trees and six species of lianas growing in multiple plots in a common garden in Panama. All trees and lianas were planted at the same time and were allowed to grow for six years in full sun. We used the evaporative flux method (EFM) for maximum hydraulic conductance and stomatal conductance measurements, and osmometry to measure turgor loss point.
Results/Conclusions
Leaf hydraulic conductance and stomatal conductance in both trees and lianas were significantly higher during the wet season compared to the dry season (Mean Kleaf dry season: Lianas=6.54 ± 1.25, Trees=5.11 ± 1.35; Wet season: Lianas=11.25 ± 2.1, Trees=6.82 ± 2.52 mol H20 m-2 s-1). Seasonal differences indicate that plants adjust their leaf hydraulic physiology and stomatal conductance in the dry season due to water limitation. However, none of the physiological functional traits that we analyzed were different between lianas and trees within seasons. We found no significant differences in turgor loss point between seasons or life forms. Therefore, we did not find evidence to support the hypothesis that lianas have physiological functional traits that would confer greater competitive ability over that of trees. Instead, our findings indicate that the physiological functional traits that are thought to confer an advantage to liana during seasonal drought do not differ between lianas and trees.