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Lianas are more abundant in seasonal forests than in wetter forests and
are thought to perform better than trees when light is abundant and water
is limited. We tested the hypothesis that lianas perform better than trees
during seasonal drought using a common garden experiment with 12
taxonomically diverse species (6 liana and 6 tree species) in 12
replicated plots. We irrigated six of the plots during the dry season for
four years, while the remaining 6 control plots received only ambient
rainfall. In year 5, we measured stem diameters for all individuals and
harvested above- and belowground biomass for a subset of individuals to
quantify absolute growth and biomass allocation to roots, stems, and
leaves, as well as total root length and maximum rooting depth. We also
measured photosynthesis, intrinsic water use efficiency (iWUE), pre-dawn
and midday water potential, and a set of functional and hydraulic traits.
During the peak of the dry season, lianas in control plots had 54% higher
predawn leaf water potentials (ΨPD), and 45% higher photosynthetic rates
than trees in control plots. By contrast, during the peak of the wet
season, these physiological differences between lianas and trees become
less pronounced and, in some cases, even disappeared. Trees had higher SLA
than lianas; however, no other functional trait differed between growth
forms. Trees responded to the irrigation treatment with 15% larger
diameters and 119% greater biomass than trees in control plots. Liana
growth, however, did not respond to irrigation; liana diameter and biomass
were similar in control and irrigation plots, suggesting that lianas were
far less limited by soil moisture than were trees. Contrary to previous
hypotheses, lianas did not have deeper roots than trees; however, lianas
had longer roots per stem diameter than did trees. Our results support the
hypothesis that lianas perform better and experience less physiological
stress than trees during seasonal drought, suggesting clear differences
between growth forms in response to altered rainfall regimes. Ultimately,
better dry-season performance may explain why liana abundance peaks in
seasonal forests compared to trees, which peak in abundance in less
seasonal, wetter forests.
406 views reported since publication in 2019.