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Contrasting hydraulic strategies in two tropical lianas and their host trees
Johnson DM; Domec JC; Woodruff DR; McCulloh KA; Meinzer FC
American Journal of Botany
Premise of the study: Tropical liana abundance has been increasing over the past 40 years which has been associated with reduced rainfall. The proposed mechanism allowing lianas to thrive in dry conditions is deeper root systems than co-occurring trees although we know very little about fundamental liana hydraulic physiology.\r\n• Methods: To test the hypothesis that two abundant liana species would physiologically outperform their host tree under reduced water availability we measured rooting depth hydraulic properties plant water status and leaf gas exchange during the dry season in a seasonally-dry tropical forest. We also used a model to compare water use by one of the liana species and the host tree during drought.\r\n• Key results: All species measured were shallowly rooted. The liana species were more vulnerable to embolism than host trees and experienced water potentials that were predicted to result in substantial hydraulic losses in both leaves and stems. Water potentials measured in host trees were not negative enough to result in significant hydraulic losses. Model results predicted the liana to have greater gas exchange than its host tree during drought and non-drought conditions. \r\n• Conclusions: The host tree species had a more conservative strategy for maintenance of the soil-to-leaf hydraulic pathway than did the lianas it supported. The two liana species experienced embolism in stems and leaves based on vulnerability curves and water potentials. These emboli were presumably repaired prior to the next morning. However in the host tree species reduced stomatal conductance prevented leaf or stem embolism.
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