4. Discussion
In the present study, we compared hydraulic and
anatomical traits of woody
species from different biomes, tested the vulnerability segmentation
hypothesis (i.e., plant branches are more resistant to cavitation than
their roots, P 50 root - branch > 0),
and analyzed the coordination between P 50 root -
branch and environmental variables, so as to provide new insights into
how environment factors drive the vulnerability segmentation between
branches and roots. Our results showed that P 50
root - branch > 0 was common across different biomes
(tropical seasonal forest, temperate seasonal forest,
woodland/shrubland, and desert), which are consistent with the
vulnerability segmentation hypothesis. Moreover, the degree of
vulnerability segmentation between roots and branches increased with
environmental aridity, which may be attributed to the decoupling of root
and branch xylem anatomical traits, e.g., hydraulically weighted
diameters (D h) increased significantly with
aridity in branches but not in roots.