Researchers from Tohoku University developed a leaf-mounted sensor to simplify the process of determining whether a plant is prospering or dying. To satisfy ever-increasing demands, this small but powerful device could assist in increasing crop yields and resource management. The study was published in the journal Sensing and Bio-Sensing Research.
Observations of birch leaves in the autumn foliage stage over two weeks. (Top) Time-course changes across eight wavelengths. (Middle) Variation in sunlight intensity. (Bottom) Actual changes in leaf color. As the green color shifts to yellow and brown, changes in reflectance can be observed. Image Credit: Kohzuma and Miyamoto
Increasing agricultural output is critically needed as concerns about climate change and population growth increase.
Heat waves, torrential rains, and droughts are examples of extreme weather conditions that cause stress in plants, lowering crop yields and endangering the long-term viability of forests, farms, and wildlife. The need to carefully track how plants react to these changes is unfulfilled.
Drones and airplanes have made it easier to monitor plants from above, but they only record additional surface-level macro data. To track plants accurately over time, they also require changes. Since they frequently need on-site staff to install and manually inspect each sensor, other tiny sensors that may record changes at the individual plant level are troublesome.
The traditional methods may work well for some purposes, but they are difficult to operate and quite expensive. To continuously monitor small changes, we needed a new solution.
Kaori Kohzuma, Graduate School of Life Sciences, Tohoku University
A group of scientists created a unique sensor that adheres straight to the underside of plant leaves to solve these problems. This tiny gadget measures leaf color without obstructing sunlight using a spectroscopic sensor and light source.
It can also monitor variations over time in the same location. The battery-operated sensor's Wi-Fi data transfer, waterproofing, and ability to operate outside for more than a month make extended data gathering possible.
Smart agriculture is a huge time-saver. Farmers do not have time to manually check every single plant. This sensor is able to provide fine-tuned readings for what's going on in real-time. Then, they can react accordingly to areas where plants are experiencing high levels of stress.
Ko-ichiro Miyamoto, Study Corresponding Author, Department of Electronic Engineering, Tohoku University
This sensor outperformed a commercial spectrometer when tested on approximately 90 leaves from 30 distinct plant species. Its values at 620 nm were quite close to those of commercial chlorophyll meters, and it discriminated colors reliably throughout seven of its eight observable wavelengths.
Additional experiments using a mutant Arabidopsis thaliana that is sensitive to stress revealed that variations in the sensor's readings at 550 nm corresponded with the plant's stress reactions and matched the widely used Photochemical Reflectance Index (PRI).
In an outdoor experiment to evaluate performance in real-world settings, they affixed the sensor to birch leaves to monitor color changes over two weeks during autumn, fall, and aging. They could see how the plant's reaction varied with the amount of sunshine and how chlorophyll, a sign of plant stress, decreased.
This affordable sensor is a promising tool for accurately monitoring plant health and stress through leaf color and light reflection data. Its low cost makes it possible to place multiple sensors across various locations, creating a network for simultaneous monitoring in many spots.
Kaori Kohzuma, Graduate School of Life Sciences, Tohoku University
This advanced diagnostic technology enables targeted support in areas where it is most needed. The sensor has broad applications, including smart farming, forest health monitoring, and other fields requiring precise tracking of plant health.
Journal Reference:
Kohzuma, K., et al. (2024) Analysis of plant physiological responses based on leaf color changes through the development and application of a wireless plant sensor. Sensing and Bio-Sensing Research. doi.org/10.1016/j.sbsr.2024.100688.