Hydraulic differences along the water transport system of South American Nothofagus species: Do leaves protect the stem functionality?

S.J. BUCCI; F. G. SCHOLZ; P. I. CAMPANELLO; L. MONTTI; M. JIMENEZ; F. ROCKWELL; L. LAMANNA; P. GUERRA; P. LOPEZ BERNAL; O. TRONCOSSO; J. ENRICCI; M.N. HOLBROOK; G. GOLDSTEIN

TREE PHYSIOLOGY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2012 p. 1 - 14

0829-318X

Hydraulic traits were studied in six species and two populations of three species the Nothofagus genus from temperate forests of South America, with the goal of determining if properties of the water conductive pathway in stems and leaves are functionally coordinated and to assess if leaves are more vulnerable to cavitation than stems consistent with the theory of hydraulic segmentation of trees along the vascular system in ecosystems subjected to seasonal drought. Vulnerability to cavitation, hydraulic conductivity of stems and leaves, leaf water potential, wood density, and water relations of leaves were examined. Large variation in vulnerability to cavitation of stems and leaves were observed across populations and species, but leaves were consistently more vulnerable than stems. Water potential at 50% loss of maximum hydraulic efficiency (P50) ranged from –0.94 to -2.44 MPa in leaves and from-2.6 to -5.3 MPa in stems across species and populations. Populations of three species in the driest sites had sapwood and leaves more vulnerable to cavitation than those grown in the wettest sites. Stronger diurnal down-regulation in leaf hydraulic conductance compared to stem hydraulic conductivity apparently has the function to slow down potential water loss in stems and protect stem hydraulics from cavitation. Species-specific differences in wood density and leaf hydraulic conductance (KLeaf) were observed. Both traits were functionally related: species with higher wood density had lower KLeaf. Other stem and leaf hydraulic traits were functionally coordinated resulting in Nothofagus species with an efficient delivery of water to the leaves. Integrity of the more expensive woody portion of the water transport pathway thus can be maintained at the expenses of the replaceable portion (leaves) of the stem-leaf continuum under prolonged drought. Compensatory adjustments between hydraulic traits may help to decrease the rate of embolisms formation in the populations more vulnerable to cavitation.