Lianas have more acquisitive traits than trees in a dry but not in a wet forest

Lianas are increasing in relative abundance and biomass in many tropical
forests. We tested the hypothesis that lianas conform to the fast and
acquisitive end of the continuum of plant strategies, allowing lianas to
acquire resources faster than trees. We assessed functional traits
representative of the leaf (LES) and wood economics spectrum (WES),
including plant hydraulics, in 16 liana and 16 tree species in the canopy
of two tropical forests at the extremes of the climatic and geological
gradient across the Isthmus of Panama. For both forests, we observed a
trade-off between the construction of more productive leaves with rapid
turnover and expensive leaves with slower turnover. We also found trait
variation associated with wood and hydraulic traits. These two axes were
orthogonal, suggesting that trade-offs at the leaf and stem, including
plant hydraulics, operate independently. For the dry forest, lianas had
cheaper and more efficient leaves than trees. For the wet forest, lianas
and trees overlapped in leaf and stem characteristics. Moreover, the
duration of green foliage highly explained the variation between dry
forest species, reflecting different adaptations to drought. In the wet
forest, fast-growing species benefited from a higher return on investments
of leaf vascular tissues than slow-growing species and they had a higher
capacity to transport water through the leaf. A higher capacity to
construct more productive leaves and display leaves with lower costs may
favour lianas over trees in light interception, photosynthetic rates, and
growth under high light and nutrient availability in dry forests.
Synthesis: Lianas in a dry tropical forest had a more acquisitive strategy
than trees, characterized by more productive leaves and more efficient
display for light interception. In dry environments, lianas appear to
benefit from high-light and nutrient-rich soils and thus take advantage of
higher resource conditions compared to trees. By contrast, in a wet
tropical forest, lianas and trees overlapped in leaf and stem
characteristics and lianas were not more acquisitive than trees. In wet
environments, low light availability and nutrient-poor soils in a context
of low water limitation may constrain variation in resource acquisition
strategies between lianas and trees.