Functional traits of lianas differ from those of trees in a lowland tropical forest

Background/Question/Methods

Lianas (woody vines) are currently increasing in abundance and biomass in Neotropical rainforests which is likely to have significant impacts on these ecosystems, yet our understanding of why lianas are increasing is limited. Research suggests that lianas may be better adapted to the environmental conditions of global climate change (increased CO₂, temperature, drought) through their functional traits, however these studies have focused primarily on leaves. We examined root and leaf functional traits of lianas and trees on Barro Colorado Island, Panama, in order to determine trait patterns and relationships that may be associated with the increasing ecological success of lianas. Our questions were: 1) Do leaf and root traits of lianas differ from those of trees?  2) Do correlations exist between aboveground (leaf) and belowground (root) traits of lianas and trees, and if so, how do they differ between growth forms? To test this we sampled fine roots and leaves from 6 pairs of intra-familial liana and tree species (12 species total) and calculated a suite of morphological, chemical, and symbiont root and leaf functional traits. Tree-liana pairs were utilized to control for extraneous phylogenetic variation that may have hindered the detection of functional trait differences between growth forms. 

Results/Conclusions

Liana roots and leaves possessed traits for rapid resource acquisition including higher specific leaf area and specific root length, lower leaf and root tissue density, smaller root diameter, higher root branching intensity, lower leaf and root carbon (C), higher root nitrogen (N) and phosphorus (P), and lower mycorrhizal colonization than trees. These findings suggest that lianas create leaves and fine roots that efficiently acquire resources at a lower expenditure of C, but as a result, have poor structural integrity, and are likely to turnover more quickly than in trees. We also observed distinct suites of above and belowground trait relationships for each growth form. In lianas we found correlations between leaf and root tissue density, leaf thickness and root diameter, and leaf and root P concentrations, while in trees we found correlations between leaf and root N concentrations. This suggests that lianas and trees experience differing constraints on whole-plant trait coordination and highlights the integrated liana strategy of rapid resource acquisition both above and belowground. Overall, lianas may use specialized root and leaf trait syndromes to gain an ecological advantage over co-occurring trees. This study provides important insight into the mechanisms underlying liana increase in neotropical forests.