The functional mechanism behind latitudinal pattern of liana diversity:
freezing-thaw embolism reduces the ecological performance of liana
species.
Abstract
1.- There is a strong decrease in liana diversity along latitudinal and
altitudinal gradients at global scale, and there is a marked difference
in liana diversity between tropical and temperate ecosystems. From these
observations it has been proposed that cold temperatures would restrict
the liana ecological patterns, because of the vulnerability of their
vascular system to freezing-thaw embolism. However, there is scarce
empirical evidence that support this idea in natural conditions. 2.- The
goal of our study was to establish the functional mechanism behind the
loss of liana diversity towards higher latitudes. For this purpose, we
evaluated the change in liana performance and the trade-off between
safety and efficiency of water transport along a latitudinal gradient in
temperate rainforests of South America. We measured the ecological liana
performance as the apical growth rate in ten liana species along a
latitudinal gradient, and we related it with functional traits
associated with the safety (vessel diameter, vessel density, wood
density and root pressure) and efficiency of water transport (maximum
hydraulic conductivity and percentage of lost conductivity). 4.- We
found that lianas species inhabiting the southern (colder) site of the
latitudinal gradient have low performance, with a 5-fold decrease in
their apical growth rate compared to the northern sites. These would be
consequence of a much lower water transport efficiency (26.1-fold
decrease) respect to liana species that inhabit northern (warmer) sites,
as an outcome of a higher freezing-thaw embolism (37.5% of PLC) and
reduction of vessel diameter (3 times narrower). 5.- These results are
clear evidence that cold temperature restricts liana performance and
would act as a modeler of their latitudinal diversity pattern.