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. 2.- Our aim was to establish
the functional mechanism behind the loss of liana diversity along a
latitudinal temperature gradient. We evaluate the ecological liana
performance as the apical growth rate in ten liana species, and
functional traits associated with efficiency (maximum hydraulic
conductivity and percentage of lost conductivity) and the safety (vessel
diameter, vessel density, wood density and root pressure) of water
transport. 4.- We found that in the southern site (colder) of the
latitudinal gradient lianas species the have low performance, with a
5-fold decrease in their apical growth rate compared to the northern
sites (warmer). 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 unmistakable evidence that cold
temperature restricts liana performance, in cold environment liana
species exhibit a strong decrease in performance, a low efficiency and
higher safety of water transport. On the other hand, in warmer sites, we
found that liana species exhibit functional strategies associated with
higher performance, higher efficiency and low safety of water transport
capacity. This trade-off between efficiency and safety of water
transport and their effect over performance would explain the
latitudinal pattern of liana diversity