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WHOLE PLANT AND ECOPHYSIOLOGY

Do Xylem Fibers Affect Vessel Cavitation Resistance?¹

Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824–1312 (A.L.J., F.W.E., W.A.P); and Natural Science Division, Pepperdine University, Malibu, California 90263 (R.B.P., S.D.D.)

Possible mechanical and hydraulic costs to increased cavitation resistance were examined among six co-occurring species of chaparral shrubs in southern California. We measured cavitation resistance (xylem pressure at 50% loss of hydraulic conductivity), seasonal low pressure potential (P_min), xylem conductive efficiency (specific conductivity), mechanical strength of stems (modulus of elasticity and modulus of rupture), and xylem density. At the cellular level, we measured vessel and fiber wall thickness and lumen diameter, transverse fiber wall and total lumen area, and estimated vessel implosion resistance using (t/b)_h², where t is the thickness of adjoining vessel walls and b is the vessel lumen diameter. Increased cavitation resistance was correlated with increased mechanical strength (r² = 0.74 and 0.76 for modulus of elasticity and modulus of rupture, respectively), xylem density (r² = 0.88), and P_min (r² = 0.96). In contrast, cavitation resistance and P_min were not correlated with decreased specific conductivity, suggesting no tradeoff between these traits. At the cellular level, increased cavitation resistance was correlated with increased (t/b)_h² (r² = 0.95), increased transverse fiber wall area (r² = 0.89), and decreased fiber lumen area (r² = 0.76). To our knowledge, the correlation between cavitation resistance and fiber wall area has not been shown previously and suggests a mechanical role for fibers in cavitation resistance. Fiber efficacy in prevention of vessel implosion, defined as inward bending or collapse of vessels, is discussed.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.058404.

^* Corresponding author; e-mail jacob115{at}msu.edu; fax 517–353–1926.

Received December 17, 2004; returned for revision May 16, 2005; accepted June 14, 2005.

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