Embolism vulnerability in drought-deciduous and evergreen species of a tropical dry forest

Plant water status plays an important role in determining phenological patterns of leaf expansion and abscission of drought-deciduous (DC) and evergreen (EG) species co-occurring in tropical dry forests. Ii vulnerability to embolism is related to the phenological pattern, we should find that drought-deciduous species are intrinsically more susceptible than evergreen species to drought-induced embolisms. The object of this study was to assess the embolism vulnerability curves and the percentage loss of hydraulic conductivity (PLC) due to embolisms in four DC and two EG species from a tropical dry forest in Venezuela. In DC, PLC was between 8 and 19% during the wet season but a significant increase to between 38 and 79% occurred during the dry season. Increment of embolism in EG was from 30 to 35% during the wet season to between 40 and 48% during the dry season. Regarding embolism vulnerability curves, a clear-cut difference between DC and EG species was not observed. Both plant types underwent 50 PLC al a cavitation tension between 1.65 and 3.82 MPa. In conclusion, the degree of embolism in DC and EG was not determined by differences in vulnerability curves. Moreover, no interrelation was found between xylem efficiency and tension at 50 PLC embolisms. Differences in root depth and water availability between DC and EG seemed to be the underlying cause of embolism in the field. Nevertheless, the occurrence of a lower susceptibility to drought-induced embolisms in the dominant tree B. cumanensis implied that risk from xylem dysfunction may have some ecological significance.