Print PageAs 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, and whether any response differs between the wet and dry seasons. We are investigating 8 locally abundant tropical liana and tree species growing in open-top chambers in Panama.
Results/Conclusions
Preliminary results suggest that, during the wet season, lianas exhibit a larger response (change in stem height and diameter) than trees to elevated CO2 concentrations when compared to ambient concentrations. Lianas also respond with higher rates of photosynthesis and stomatal conductance. However, during the first six weeks of the dry season, the results are mixed: elevated CO2 leads to greater growth in liana diameter and leaf productivity than trees, yet trees exhibit the larger change in stem height. The liana and tree responses are each controlled by a subset of species, instead of a uniform response within growth form. This is the first study to assess whether the combination of increasing CO2 and seasonal drought is a viable explanation for the observed increase in liana size and abundance in the tropics.
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