Although previous studies have suggested that lianas exhibit superior growth compared to trees during dry seasons, their strategies for acquiring water remain poorly understood. This study investigated the water uptake depth and above-ground functional traits of 10 liana species and 11 tree species coexisting in a seasonally dry tropical evergreen forest in Cambodia. Using stable oxygen isotopes, we estimated dry-season water uptake depths and compared five functional traits, including specific leaf area (SLA), leaf nitrogen (LNC) and phosphorus content (LPC), stable carbon isotope ratio (δ13C) of leaves, and wood density (WD). Both lianas and trees absorbed water mainly from middle to deep soil layers, with no significant difference in water uptake depth. We found substantial variation in water uptake depth even within the same life-form, with some species relying on shallow soil water and others accessing much deeper sources, indicating diverse water acquisition strategies during the dry season. With slightly higher SLA and lower WD, lianas showed a relatively acquisitive carbon- and nutrient-use strategy compared to trees; however, there was no significant difference in water use efficiency, as represented by leaf δ13C. Patterns of trait coordination among multiple organs differed between lianas and trees. In lianas, deeper water uptake was positively correlated with less negative leaf δ13C, whereas in trees this relationship was negative as well as weak. This divergence highlights different functional strategies even under similar environmental pressures. Our findings underscore the fact that lianas did not consistently use deeper water or show higher water use efficiency than trees in this ecosystem. Instead, trait variations and the coordination between above- and below-ground traits may help explain the success of lianas in seasonally dry environments.
Hiiragi et al. (Thu,) studied this question.