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Updated: Oct 11, 2025
08:31
The Calibration and Use of Capacitance Sensors to Monitor Stem Water Content in Trees
Published on: December 27, 2017
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Forest system hydraulic conductance: partitioning tree and soil components.
Oliver Binks1, Lucas A Cernusak2, Michael Liddell2
1Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia.
The New Phytologist
|December 3, 2021
Summary
This study introduces a novel in-situ method to measure whole-tree hydraulic conductance (ktree) and soil conductance (ksoil) in tropical rainforests. Results show environmental factors like vapor pressure deficit significantly influence these crucial plant water transport parameters.
Area of Science:
- Plant physiology
- Ecosystem science
- Hydrology
Background:
- Soil-leaf hydraulic conductance is vital for canopy-atmosphere interactions in vegetation models.
- Current methods rely on ex-situ measurements, limiting accuracy for whole-tree and soil conductance.
- Accurate in-situ measurements are needed for tropical rainforests.
Purpose of the Study:
- To develop and apply a novel in-situ approach for estimating whole-tree conductance (ktree), functional soil conductance (ksoil), and system conductance (ksystem).
- To investigate the influence of environmental factors, species, and tree size on these hydraulic conductances at two tropical rainforest sites.
- To compare in-situ derived conductances with alternative representations.
Main Methods:
- Utilized in-situ measurements of soil water potential (Ψsoil) and sap flux data to determine functional rooting depth for each tree.
- Calculated whole-tree conductance (ktree) and functional soil conductance (ksoil) based on functional rooting depth.
- Analyzed variations in ktree and ksoil across species, size classes, seasons, height above nearest drainage (HAND), and field sites.
Main Results:
- In-situ estimates for ktree, ksoil, and ksystem were successfully derived at two tropical rainforest sites.
- ktree was lower and showed seasonal variation at the site with higher vapor pressure deficit (VPD) and rainfall.
- Soil resistance (rsoil) varied significantly with season, being negligible in the wet season and substantial in the dry season, while ktree scaled with tree circumference.
Conclusions:
- Vapor pressure deficit (VPD), rather than rainfall, may be a key driver of plot-level hydraulic conductance.
- Leaf water potentials and sap flux measurements are effective for determining tree and soil hydraulic conductances.
- Ψsoil profiles offer valuable mechanistic insights into ecosystem-level water fluxes, improving vegetation models.
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