The hydraulic efficiency–safety trade‐off differs between lianas and trees

Abstract

Hydraulic traits are important for woody plant functioning and distribution. Associations among hydraulic traits, other leaf and stem traits, and species’ performance are relatively well understood for trees, but remain poorly studied for lianas. We evaluated the coordination among hydraulic efficiency (i.e., maximum hydraulic conductivity), hydraulic safety (i.e., cavitation resistance), a suite of eight morphological and physiological traits, and species’ abundances for saplings of 24 liana species and 27 tree species in wet tropical forests in Panama. Trees showed a strong trade‐off between hydraulic efficiency and hydraulic safety, whereas efficiency and safety were decoupled in lianas. Hydraulic efficiency was strongly and similarly correlated with acquisitive traits for lianas and trees (e.g., positively with gas exchange rates and negatively with wood density). Hydraulic safety, however, showed no correlations with other traits in lianas, but with several in trees (e.g., positively with leaf dry matter content and wood density and negatively with gas exchange rates), indicating that in lianas hydraulic efficiency is an anchor trait because it is correlated with many other traits, while in trees both efficiency and safety are anchor traits. Traits related to shade tolerance (e.g., low specific leaf area and high wood density) were associated with high local tree sapling abundance, but not with liana abundance. Our results suggest that different, yet unknown mechanisms determine hydraulic safety and local‐scale abundance for lianas compared to trees. For trees, the trade‐off between efficiency and safety will provide less possibilities for ecological strategies. For lianas, however, the uncoupling of efficiency and safety could allow them to have high hydraulic efficiency, and hence high growth rates, without compromising resistance to cavitation under drought, thus allowing them to thrive and outperform trees under drier conditions.

Lianas have a seasonal growth advantage over co‐occurring trees

“…; C. M. Smith‐Martin, C. L. Bastos, O. R. Lopez, J. S. Powers, and S. A. Schnitzer, unpublished data ), and by maintaining healthy water status and maintaining high hydraulic conductivity during the dry season (e.g., van der Sande et al., ), lianas are particularly well suited to take advantage of high dry‐season light availability. By contrast, trees appear to suffer more water stress (C. M. Smith‐Martin, C. L. Bastos, O. R. Lopez, J. S. Powers, and S. A. Schnitzer, unpublished data ) and have a more conservative hydraulic conductivity strategy than lianas (van der Sande et al., ), and thus trees may not be able to capitalize as well as lianas on the high dry season light. The ability of lianas to capitalize on high solar radiation while maintaining healthy water status may also explain their extremely high abundance in such high‐light areas as treefall gaps, forest edges, and young tropical forests (reviewed by Schnitzer ).…”

“…In an examination of physiological traits of liana and tree saplings that were growing along roadsides in wet and seasonal forests in Panama, van der Sande et al. () reported that trees had the expected trade‐off between hydraulic conductance and hydraulic safety, whereas lianas did not, suggesting that lianas had the capacity to maintain high conductivity and thus high growth rates while resisting embolism. Collectively, these studies suggest that lianas are better able to grow during the dry season than co‐occurring trees, and thus are able to capitalize on high dry season light availability.…”

Long‐term dynamics of liana seedlings suggest decelerating increases in liana relative abundance over time

“…The proliferation of lianas appears to be driven by both higher survival and higher recruitment of lianas compared to trees, particularly in the first eight years of the study. Higher recruitment could reflect a past increase in liana seed production, while both higher recruitment and survival likely reflect a potential physiological advantage that allows liana seedlings to establish and survive better than tree seedlings (van der Sande et al, ). Despite the hypothesized effects of water availability and canopy gaps in driving the increasing prevalence of lianas, we did not find differences in demography between liana and tree seedlings related to habitat type, nor any relationship between changes in liana seedling relative abundance and annual rainfall, dry season length or proportion of area in gaps.…”

Wood allocation trade‐offs between fiber wall, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees

“…An evolutionary trade‐off between xylem water transport efficiency and xylem hydraulic and mechanical safety has been proposed to explain interspecific differences in drought resistance (Baas, Ewers, Davis, & Wheeler, ; Chave et al, ). However, recent studies show that generally, there is a weak trade‐off between hydraulic safety and efficiency, with many species showing both a low hydraulic safety and low hydraulic efficiency (Gleason et al, ; van der Sande, Poorter, Schnitzer, Engelbrecht, & Markesteijn, ). These findings limit the generalization and broader implementation of the safety‐efficiency trade‐off hypothesis in modeling frameworks and illustrate that the underlying mechanisms driving interspecific differences in drought resistance are still poorly understood in highly diverse tropical forests.…”