Scientists have developed an open-source instrument that can measure how much water plants have without hurting them, helping us understand plants better and use water for farming more wisely.

Scientists have long sought new ways to continuously monitor how changing water availability affects plants. Traditional methods of measuring water potential, a key indicator of plant water stress, require invasive sampling that damages tissue. Now researchers have developed entirely open-source instruments capable of tracking plant water status with unprecedented high frequency and non-destructive precision. The development, carried out in the USDA, was published in AoB PLANTS.

Dendrometers are sensors that measure radial stem changes driven by plant water dynamics. Most existing designs have limitations for long-term continuous monitoring. However, a team led by Sean Gleason has created a novel contact dendrometer that overcome these issues. By combining dendrometer data with periodic conventional water potential measurements, their device can estimate water potential every minute or less with minimal disturbance on plant tissues exhibiting little or no secondary growth (petioles, monocotyledon stems).  

Our focus with this study was not to confirm the already reported relationship between diameter variation and water potential, but rather, to describe the development of an inexpensive sensor that would make high-resolution diameter measurement devices available to anyone with a need for diameter data, as well as traits that can be derived  from these data. As such, the sensor, software and analysis tools required to collect and make sense of these measurements needed to be entirely open-source, free or  inexpensive and straightforward to build, modify and share with others. 

Gleason et al. 2024

In laboratory trials, the researchers tested both dendrometers on sunflower and corn during simulated drying and watering cycles. The contact sensor is affixed directly to plant stems, while the optical version employs a non-touching technique. Remarkably, the two methods showed very close agreement with each other and with direct water potential readings. They detected subtle 50 kPa differences corresponding to slight changes in transpiration, vapor pressure and soil moisture levels. 

Contact dendrometer design and use. Adjustable PLA filament version of contact dendrometer requiring elastic bands (A), non-adjustable PLA filament version of contact dendrometer (B) and resin-printed compression spring design (C). Contact dendrometer placed on Helianthus petiole (D), and Zea stem (E). Source: Gleason et al. 2024

To demonstrate real world use, the team deployed the contact dendrometer on sumac (Rhus typhina) branches in an outdoor setting for a week. It continuously recorded natural fluctuations in branch diameter driven by the plant’s water status.  

Two key advantages to using this new dendrometer for quantifying water potential are its high temporal sampling frequency, measuring in seconds, and the ability to sample at multiple points across the same plant or organ. Additionally, all hardware designs, software and instructions are published openly for anyone to replicate and improve upon the design. 

Being able to monitor plant water relations so frequently and non-invasively opens new opportunities for research. Scientists can gain deeper insights into physiological responses under stressful conditions, and growers may find ways to manage irrigation more sustainably by precisely tracking crop water needs. With open sourcing ensuring accessibility, these novel dendrometers have the potential to advance our understanding and management of plant water relations worldwide, offering a game-changing tool for both research and sustainable agriculture. 

READ THE ARTICLE 

Gleason S., Stewart J., Allen B., Polutchko K., McMahon J., Spitzer D. and Barnard D.  (2024). “Development and application of an inexpensive opensource dendrometer for detecting xylem water potential and radial stem growth at high spatial and temporal resolution” AoB PLANTS.  Available at: https://doi.org/10.1093/aobpla/plae009

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