Hydraulic vulnerability segmentation between branches and roots
increases with environmental aridity
Abstract
The hydraulic vulnerability segmentation hypothesis proposes that plant
branches are more resistant to cavitation than roots, namely, the
difference in vulnerability to cavitation between branches and roots is
positive ( P 50 root - branch > 0).
However, it is not clear how this phenomenon can vary along
environmental aridity gradients. We compiled the above hypothesis with
105 woody species from four biomes with increasing aridity, by compiling
functional traits related to hydraulic properties and anatomical
structures of branches and roots. We investigated the relationships
between P 50 root - branch and several
environmental factors that are associated with aridity. We found a
positive P 50 root - branch across species, which
supported the hydraulic vulnerability segmentation hypothesis, and
P 50 root - branch increased significantly with
environmental aridity. Branch xylem hydraulic conductivity changed from
“more efficient” (e.g., wider conduit, higher hydraulic conductivity)
to “safer” (e.g., narrower conduit, more negative P
50) in response to increased aridity, while root xylem
hydraulic conductivity remained unchanged across aridity gradients. Our
results demonstrated that hydraulic vulnerability segmentation is more
pronounced for species from arid regions. Changes in branch traits may
be responsible for hydraulic vulnerability segmentation between branches
and roots.