Physiological and morphological evidence of niche segregation between two co-occurring species ofAdenostomain California Chaparral

Abstract

Abstract:We tested the hypothesis that co-occurring, congeneric species of Adenostoma (chamise = A. fasciculatum and red shank = A. sparsifolium) in the Santa Monica Mountains of southern California have physiological differences in water relations that possibly contribute to niche segregation and species coexistence. We did this by comparing (1) seasonal changes in water potential at predawn and midday, (2) diurnal changes in water potential, stomatal conductance to water vapor diffusion and transpiration rates in spring and fall, (3) vulnerability of xylem to water stress-induced embolism, and (4) hydraulic transport properties of stem xylem. A. fasciculatum showed greater seasonal water stress than A. sparsifolium in the fall of 1990 after 4 years of drought (midday water potentials of -8 MPa versus -4 MPa) and also in the fall of 1991 after a year of normal precipitation (-5 MPa versus -3 MPa). A. fasciculatum had higher stomatal conductance and transpiration rates than A. sparsifolium during spring m...