Tatsuya Yamashita

Growth control of leaf lettuce with exposure to underwater ultrasound and dissolved oxygen supersaturation

The growth rate of vegetables in plant factories can be regulated by environmental factors including light, temperature, and chemicals, which might give rise to mutation in leaf health. Here, we aim to devise a new way that allows for controlling the growth rate of plants in hydroponics as well as maintaining the product quality; we apply underwater ultrasound and dissolved oxygen supersaturation as external stimuli to plants. As an example, we examine the growth of leaf lettuce in hydroponics with exposure to 28-kHz ultrasound and dissolved oxygen supersaturation up to 36 mg/L at 20 °C. Our results show that exposure to the ultrasound of peak-to-peak pressure at 20 kPa or larger works as the growth inhibitor of the leaves and the roots, while the oxygen supersaturation as the growth promoter, without any degradation of chlorophyll in the leaves. This suggests that these external stimuli can be used in the growth control system of plant factories.

Effect of underwater ultrasound exposure on growth of plant roots and leaves

Growth control is an important technique in plant markets, for appropriate shipping time of plants (e.g., flowers and fruits) allows for reducing production costs for post harvesting storage and pesticide. It is favorable to control plant growth without any chemicals; physical stresses are attractive candidates for this purpose. Here, we propose an ultrasound-based technique to control plant growth.