Woody species of a semi-arid community are only moderately resistant to cavitation

Vulnerability to drought-induced cavitation and seasonal water relations of six shrub species with different functional traits (deep v. superficial roots; evergreen v. summer deciduous; leaves v. cladodes) were measured in a semi-arid plant community strongly limited by water availability. The underlying hypotheses were that species would differ in their hydraulic properties and resistance to drought, reflecting different adaptations to a common environment and that individual adaptations may involve tradeoffs that would cause hydraulic properties to co-vary. Species experiencing the lowest minimum leaf water potentials generally had lower stomatal conductance, but they were not more resistant to xylem embolism than species with higher leaf water potentials and stomatal conductance. Overall, the studied species were more vulnerable to xylem embolism than expected and experienced high rates of native embolism and percent of leafless branches during summer drought. However, recovery rates from leafless branches were also high. Xylem resistance to embolism varied between species but had no relationship with minimum leaf water potential, suggesting that (i) adaptation to arid environments does not necessarily imply high resistance to embolism; and (ii) the costs associated with embolism resistance can be compensated by other components of the hydraulic strategy of a given species.