Development and application of an inexpensive open-source dendrometer for detecting xylem water potential and radial stem growth at high spatial and temporal resolution

Authors: Gleason, Sean; STEWART, JARED - Collaborator; Allen, Brendan; Polutchko, Stephanie; McMahon, Jordan; Barnard, David; Spitzer, Daniel

Submitted to: AoB Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2024
Publication Date: 2/28/2024
Citation: Gleason, S.M., Stewart, J.J., Allen, B.S., Polutchko, S.K., McMahon, J.E., Barnard, D.M., Spitzer, D.B. 2024. Development and application of an inexpensive open-source dendrometer for detecting xylem water potential and radial stem growth at high spatial and temporal resolution. AoB Plants. 16(2). Article plae009. https://doi.org/10.1093/aobpla/plae009.
DOI: https://doi.org/10.1093/aobpla/plae009

Interpretive Summary: There is a need for a low-cost, non-invasive method to measure the potential energy of liquid water (hereafter: water potential) in plant tissue precisely and quickly. We developed a novel application of an already existing tool, called a "dendrometer" to address this. Our open source dendrometer can detect very small changes in stem and petiole diameter (1 micron). Combined with periodic measurements using standard devices, our calibrated dendrometer offers water potential readings in time steps less than five seconds. The dendrometer works well on grass stems and the petioles and branches of woody plants. The dendrometer is easy to connect to a computer in a lab or outdoors using open-source software and costs under $10 to build. We compared it to another tool, the "optical" dendrometer, and tested both on different plants (sunflower and maize) in controlled settings. We also used it to track changes in woody dicotyledon branches (sumac) in the field. Both dendrometers aligned well with each other and matched measurements taken using commercially available devices and effectively captured small shifts in stem water potential resulting from small differences in light, vapor pressure, and soil moisture. The optical dendrometers slightly outperformed our design due to their non-contact design. Detailed information, including setup and software, is provided in this study.

Technical Abstract: There is currently need for inexpensive, continuous, non-destructive water potential measurements at high temporal resolution (< 1 min). We describe here the development and testing of an entirely open source dendrometer that, when combined with periodic Scholander pressure bomb measurements, provides sub-minute resolution in water potential when placed on tissues exhibiting little or no secondary growth (petioles, monocotyledon stems). The dendrometer can also be used to measure radial growth on stems and branches when placed on woody dicotyledons. The dendrometer can be interfaced directly with a computer in real time in the lab or greenhouse, or be interfaced with an open source datalogger for long periods of use in the field on batteries. The entire system (four dendrometers, control board/datalogger) can be built from non-brand electronics and run on entirely open source software (preferred) for less than ten US dollars. We compare our device (hereafter “contact” dendrometer) with another recently developed open source dendrometer (“optical” dendrometer; https://cavicams.com/) on a herbaceous dicotyledon (Helianthus annuus) and monocotyledon (Zea mays) grown for one week in a walk-in growth chamber. We also demonstrate the ability of the device to record branch and trunk diameter variation in the field on a woody dicotyledon (Rhus typhina). Overall, contact and optical dendrometers were well aligned with one another, with Pearson correlation coefficients ranging from 0.77 to 0.97 for all contact vs optical correlations. Both dendrometer devices were also well aligned with pressure chamber measurements on adjacent “sacrifice” plants, with calibration curves exhibiting significant non-linearity, especially at water potentials below the point of incipient plasmolysis, with pseudo-r2 values (Eron) ranging from 0.89 to 0.99. Overall, the both dendrometers detected subtle changes in stem water potential (~50 kPa) resulting from light-induced changes in transpiration, VPD, and drying/wetting soils, although the optical dendrometers performed better sensing small increases in stem water potential, owing to their non-contact design. All hardware designs, alternative configurations, software, and build instructions for the contact dendrometers are provided.