Topography strongly affects drought stress and xylem embolism resistance in woody plants from a karst forest in Southwest China

1. Xylem resistance to drought-induced embolism is an important trait
determining plant distribution. In the karst hills of Southwest China,
with a relatively small variation in altitude, soil depth and water
availability strongly decrease from the foot towards the top, and woody
plant species display distinct spatial distribution. 2. For testing the
hypothesis that embolism resistance of leaf and stem xylem reflects the
spatial distribution across species along a topographical gradient of the
karst hills, we measured the xylem water potential in the dry season,
vulnerability to drought-induced embolism in stems and leaves, and
relevant anatomical traits in 17 evergreen species with a different
topographical distribution. 3. We found that from the foot towards the
hill top, plant water potential sharply decreased, and both stem and leaf
xylem showed increasing resistance to hydraulic dysfunction and
drought-resistant anatomical characteristics, but non-significant
variation in specific hydraulic conductivity. Also, hydraulic safety
margins increased with relative altitude and thus increasing water
deficit, which underlies the local distribution of the species, but does
not come at the cost of hydraulic efficiency. 4. Our results demonstrate
that plant hydraulic safety largely shape the niche differentiation and
hence community assembly in highly heterogeneous and water-limited
landscapes.