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(American Journal of Botany. 2007;94:809-818.)
© 2007 Botanical Society of America, Inc.

Physiology and Biochemistry

Drought response of two Mexican oak species, Quercus laceyi and Q. sideroxyla (Fagaceae), in relation to elevational position1

H. M. Poulos2, U. M. Goodale and G. P. Berlyn

School of Forestry and Environmental Studies, Yale University, 370 Prospect St., New Haven, Connecticut 06511 USA

ABSTRACT

To investigate the relationship between the altitudinal distribution of Quercus laceyi and Q. sideroxyla and their physiological responses to drought, we measured relative water content (RWC), water potentials ({Psi}predawn and {Psi}midday), photosynthesis (Amax), stomatal conductance (g), chlorophyll fluorescence (Fv/Fm), and spectral reflectance (400–1100 nm) five times during a 7 wk acute drought. Quercus laceyi was drought tolerant, while Q. sideroxyla was a drought avoider; Q. laceyi tolerated lower RWC (Q. sideroxyla = 54%, Q. laceyi = 44%), {Psi}pd (Q. sideroxyla = –2.6 MPa, Q. laceyi = –3.3 MPa), and {Psi}md (Q. sideroxyla = –4.5 MPa, Q. laceyi = –6.6 MPa). The Fv/Fm also declined first in Q. sideroxyla in wk 6, whereas Fv/Fm did not decline in Q. laceyi until wk 7. Amax and g fell in wk 4, 6, and 7 in drought seedlings of both species, suggesting a decline in CO2 assimilation during the drought. Leaf spectral reflectance increased with time in response to decreases in leaf photosynthetic pigment concentrations in latter weeks of the drought. The results suggest a close association between the altitudinal distributions of these species and their adaptation to water stress.

Key Words: chlorophyll fluorescence • elevation gradient • Fagaceae • photosynthetic efficiency • Quercus • spectral reflectance • stress physiology • water relations






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