Ecological implications of xylem cavitation for several Pinaceae in the Pacific Northern USA

Abstract

1. Xylem hydraulic properties and vulnerability to cavitation(determined using the air-injection method) were studied in six Pinaceaeof the northern Rocky Mountains: Pinus ponderosa, Pseudotsuga menziesii,Larix occidentalis, Pinus contorta, Pinus albicaulis and Abieslasiocarpa. We tested whether species extending into drier habitatsexhibited increased resistance to water stress-induced cavitation, andwhether there is a trade-off between xylem transport capacity andresistance to cavitation.2. At lower elevations the more drought-tolerant P. ponderosa was muchless resistant to cavitation than the codominant P. menziesii. Greatervulnerability to cavitation in P. ponderosa was compensated for, atleast in part, by increased stomatal control of water loss (inferredfrom carbon isotope discrimination) and by increased sapwood to leafarea ratios. Similar differences, but less pronounced, were found incodominant species at higher elevations.3. Leaf specific hydraulic conductivity was negatively correlated withmean cavitation pressure. When species were separated into pines andnon-pines, sapwood specific conductivity and mean cavitation pressurewere also negatively correlated within each of the two groups.4. Our results indicate that within the evergreen conifers examined,greater resistance to water stress-induced cavitation is not requiredfor survival in more xeric habitats, and that there is a trade-offbetween xylem conductance and resistance to cavitation.