Stomatal structure and physiology do not explain differences in water use among montane eucalypts

Area of Science:

• Physiological ecology
• Forest hydrology
• Plant water relations

Background:

• Understanding whole-tree water use is crucial for predictive hydrology in forested catchments.
• Eucalypt species dominate high-elevation catchments in southeastern Australia.

Purpose of the Study:

• To investigate if whole-tree water use in three eucalypt species relates to stomatal anatomy, stomatal conductance (g(s)) sensitivity, and sapwood area.
• To determine the primary regulators of water use at the whole-tree scale in montane eucalypts.

Main Methods:

• Quantified daily tree water use across three eucalypt species.
• Assessed stomatal anatomy, stomatal conductance (g(s)) sensitivity to vapor pressure deficit (VPD), and maximum potential stomatal conductance (g(max)).
• Measured sapwood area and sap velocity.

Main Results:

• Daily tree water use varied sixfold among species, with parallel variation in sap velocity and sapwood area.
• Stomatal structure and physiology did not explain species-specific water use differences.
• Fastest (E. delegatensis) and slowest (E. pauciflora) water-using species showed high physiological control of g(s) (VPD sensitivity) and low anatomical control (high g(max)).
• E. radiata (intermediate water use) had g(s) insensitive to VPD and lowest g(max).

Conclusions:

• Stomatal anatomy knowledge aids understanding of leaf-level water loss regulation but has limited utility for explaining whole-tree water use in montane eucalypts at catchment scales.
• Sapwood area and sap velocity appear to be more significant predictors of whole-tree water use in these species.
• Further research into the interplay of hydraulic and anatomical traits is needed for comprehensive water use modeling.