experience and cavitation resistance in six shrubs from the Great Basin

Shrubs of the Great Basin desert in Utah are subjected to a prolonged summer drought. One poten-tial consequence of drought is a reduced water transport capability of the xylem. This is due to drought-induced cavitation. We used the centrifuge method to measure the vulnerability of root and stem xylem to cavitation in six native shrub species. The shrubs fall into three categories with regards to rooting depth, vegetative phenology and plant water status during drought. The “sum-mer green ” group (Chrysothamnus viscidiflorus, Atriplex canescens, Atriplex confertifolia) sustains summer drought with a relatively shallow root system (<2.5 m), but maintains leaf area. A “drought deciduous ” group (Grayia spinosa, Tetradymia glabrata) has shallow roots but responds to drought by dropping leaves. A “phreatophytic ” group (e.g. Chrysothamnus nauseosus) avoids low water potentials by developing a deep root system that gives them access to deeper soil mois-ture. We hypothesized that cavitation resistance across these groups was adjusted to the amount of drought stress a species experienced. Drought experience was quantified by measuring plant water potentials over two growing seasons. As expected, we found a significant relationship between the cavitation resistance of roots and stems of a species and the minimum seasonal water potential