The functional mechanism behind latitudinal pattern of liana diversity: freezing-thaw embolism reduces the ecological performance of liana species.

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