Tropical lianas and trees under elevated CO2: Growth and physiological response

Background/Question/Methods

As atmospheric CO₂ levels continue to rise, whether we can rely on forests as carbon sinks (45% of terrestrial carbon) depends on our ability to understand the dynamics behind terrestrial and atmospheric interactions. One concern is the increase in the abundance, size, and dominance of native lianas (woody climbing vines) in tropical forests. Lianas are associated with an increased risk of tree mortality, and may alter forest species composition by disproportionately colonizing non-pioneer tree species. Moreover, lianas have more efficient water transport systems and may have deeper roots, thus are capable of extending growth in the canopy during periods of seasonal drought when many tropical trees are photosynthetically less active, deciduous, or otherwise water-stressed. Our goal is to determine whether there is any difference in the growth and physiological response of tropical lianas and trees grown under elevated CO₂. We are investigating 16 locally abundant tropical liana and tree species growing in open-top chambers in Panama.

Results/Conclusions

Preliminary results suggest that, during the dry season, lianas exhibit a larger response (change in stem height) than trees to elevated CO₂ concentrations when compared to ambient concentrations. The liana response is controlled by a subset of three species, instead of a uniform increase across all eight liana species under study. On the other hand, there is little or no response to increased CO₂ among the eight tree species. If this pattern is representative of tropical liana and tree communities, we anticipate increasing liana dominance by selected species in the tropics as atmospheric levels of CO₂ continue to rise. This is one of the first studies in the tropics to assess whether increasing CO₂ is a viable explanation for the observed increase in liana size and abundance.