Jerkins, Evin G. , Pratt, R. Brandon , Jacobsen, Anna L. , Ewers, Frank W. , Davis, Stephen D. .
Xylem Cavitation Resistance among Chaparral Seedlings Grown in Shade versus Sun.
THE ability to resist xylem cavitation was examined among three species of chaparral seedlings grown in a common garden under full sun and deep shade treatments. The three species selected were Ceanothus megacarpus, Ceanothus oliganthus, and Rhamnus californica. These species represent three different life history types among chaparral shrubs: non-sprouters after fire (NS), facultative sprouter after fire (FS), and obligate sprouters after fire (OS). Typically NS recruit seedlings into open canopy microsites, FS into mixed microsites, and OS into deeply shaded microsites. We tested two hypotheses: 1) shade treated seedlings are more susceptible to water stress-induced cavitation of their stem and root xylem than seedlings grown in full sunlight and 2) plasticity in cavitation resistance between sun and shade treatments will be greatest for NS, intermediate for FS, and least for OS. We constructed vulnerability curves to xylem cavitation for all three species using a centrifuge method. The stems of the non-sprouter, C. megacarpus, grown in shade, reached 50% cavitation at a xylem pressure of -2 MPa whereas seedlings gown in sun reached 50% cavitation at -8 MPa. In the case of the obligate sprouter, R. californica, the difference between shade and sun treatment was -1.8 MPa versus -2.2 MPa. The resulting differences in water potential at 50% cavitation between sun and shade (?50) was 6 MPa for the non-sprouter, 4 MPa for the facultative sprouter, and 0.4 MPa for the obligate sprouter. Root susceptibility to xylem cavitation between sun and shade followed a similar pattern. These results suggest that seedlings grown in the shade have lower drought tolerance characteristics of their stem and root xylem than seedlings grown in sun and are consistent with life history type; non-sprouters are impacted more than sprouters.
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1 - Michigan State University, Department of Plant Biology, 166 Plant Biology Building, East Lansing, Michigan, 48824-1312, USA
2 - California State University Bakersfield, Department of Biology, 9001 Stockdale Hwy., Bakersfield, California, 93311-1099, USA
3 - Pepperdine University, Natural Sciences Division, 24255 Pacific Coast Highway, Malibu, California, 90263-4321, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, August 1st, 2006
Time: 9:15 AM