Cavitation Resistance Among 26 Chaparral Species of Southern California

Abstract

Resistance to xylem cavitation depends on the size of xylem pit membrane pores and the strength of vessels to resist collapse or, in the case of freezing-induced cavitation, conduit diameter. Altering these traits may impact plant biomechanics or water transport efficiency. The evergreen sclerophyllous shrub species, collectively referred to as chaparral, which dominate much of the mediterranean-type climate region of southern California, have been shown to display high cavitation resistance (pressure potential at 50% loss of hydraulic conductivity; P 50 ). We examined xylem functional and structural traits associated with more negative P 50 in stems of 26 chaparral species. We correlated raw-trait values, without phylogenetic consideration, to examine current relationships between P 50 and these xylem traits. Additionally, correlations were examined using phylogenetic independent contrasts (PICs) to determine whether evolutionary changes in these xylem traits correlate with changes in P 50 . Co-occurring chaparral species widely differ in their P 50 (À0.9 to À11.0 MPa). Species experiencing the most negative seasonal pressure potential (P min ) had the highest resistance to xylem cavitation (lowest P 50 ). Decreased P 50 was associated with increased xylem density, stem mechanical strength (modulus of rupture), and transverse fiber wall area when both raw values and PICs were analyzed. These results support a functional and evolutionary relationship among these xylem traits and cavitation resistance. Chaparral species that do not sprout following fire but instead recruit post-fire from seed had the greatest resistance to cavitation, presumably because they rely on post-fire survival of seedlings during the summer dry period to persist in the landscape. Raw values of hydraulic vessel diameter (d h ), maximum vessel length, and xylem-specific hydraulic conductivity (K s ) were correlated to P 50 ; however, d h , maximum vessel length, and K s were not correlated to P 50 when analyzed using PICs, suggesting that these traits have not undergone correlated evolutionary change. We found no difference in xylem traits between species occurring at freezing vs. nonfreezing sites, although freezing has been shown to affect the survival and distributions of some chaparral species. Stem mechanical strength, fiber properties, and post-fire regeneration type appear to be key factors in the evolution of cavitation resistance among chaparral shrubs.

Morphological traits and water use strategies in seedlings of Mediterranean coexisting species

“…High photosynthetic rates and the correspondingly high stomatal conductance must be supported by high hydraulic conductance (Mencuccini and Comstock 1999;Hubbard et al 2001;Sellin and Kupper 2007). Under optimal soil water supply, high K As allows more efficient water transport from stems into photosynthetic organs to compensate leaf water loss and consequently maintain daily water potential high (Ackerly 2004;Jacobsen et al 2007b). However, in this study there was no significant correlation among sapwood area: photosynthetic area ratio (A S :A P ) and K As .…”

“…These results suggest that changes in xylem anatomy (i.e., vessel size and density) among species could be related to plant functional strategies. Previous studies have suggested that there may be a range of ecologically significant vessel strategies available to species (Ackerly 2004;Preston et al 2006;Jacobsen et al 2007b).…”

Hydraulic integration and shrub growth form linked across continental aridity gradients

“…The stem segmentation index S and integration index F were not significantly correlated with each other (n ϭ 61; r ϭ Ϫ0.207; P ϭ .109; PICs: n ϭ 52; r ϭ Ϫ0.224; P ϭ .088). Stem-splitting shrubs compared with nonsplitting shrubs from dry environments ( Table 3) had higher vessel densities, smaller vessel hydraulic diameters, higher wood densities, and higher vessel implosion resistance, indicating strong resistance to drought-induced embolism formation (7,13,32).…”

The Developmental Process of Xylem Embolisms in Pine Wilt Disease Monitored by Multipoint Imaging Using Compact Magnetic Resonance Imaging

“…completely air filled; Utsumi et al, 1999Utsumi et al, , 2003Ball et al, 2006). Generally, woody plants have excellent adaptable water-conducting systems that enable them to survive through the seasonal stresses of the regional climates in which they grow (Sperry et al, 1994;Maherali et al, 2004;Jacobsen et al, 2007). However, some pathogens (e.g.…”