Impact of variable [CO2] and temperature on water transport structure-function relationships in Eucalyptus

Area of Science:

• Plant Physiology
• Ecology
• Climate Change Biology

Background:

• Whitehead's hypothesis links tree hydraulic structure and function to physiological homeostasis.
• This framework has been largely unexplored concerning varying atmospheric carbon dioxide ([CO(2)]).

Purpose of the Study:

• To evaluate Whitehead's hypothesis of leaf water potential (Ψ(l)) homeostasis in Eucalyptus saplings under elevated [CO(2)] and temperature.
• To assess if structural adjustments maintain physiological homeostasis under global change drivers.

Main Methods:

• Eucalyptus saligna and E. sideroxylon saplings were grown under three [CO(2)] levels and two temperature regimes.
• Physiological (stomatal conductance, Ψ(l)) and structural (leaf area, sapwood area, height, xylem conductivity) variables were measured.
• Relationships between structural and physiological variables were analyzed.

Main Results:

• Structural components increased with [CO(2)] or temperature; stomatal conductance decreased with [CO(2)].
• Leaf water potential (Ψ(l)) did not show homeostasis; it varied with species and temperature.
• Individual structural variables were largely uncorrelated with Ψ(l), but leaf specific hydraulic conductance (K(l)) correlated with physiological K(l).

Conclusions:

• Physiological homeostasis may not hold for saplings exposed to elevated [CO(2)] and temperature.
• Whitehead et al.'s model identified K(l) as a sensitive indicator of plant structural-physiological co-variation.