Ultra-Fine Bubble Distributions in a Plant Factory Observed by Transmission Electron Microscope with a Freeze-Fracture Replica Technique.

Tsutomu Uchida,Hitoshi Nishikawa,Masashi Asano,Naoki Noda,Nobuki Sakurai

doi:10.3390/nano8030152

Tsutomu Uchida, Hitoshi Nishikawa + Show 3 more

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https://doi.org/10.3390/nano8030152

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Abstract

Water containing ultra-fine bubbles (UFB) may promote plant growth. But, as UFBs are too small to distinguish from other impurities in a nutrient solution, it is not known if UFBs survive transport from the water source to the rhizosphere. Here we use the freeze-fracture replica method and a transmission electron microscope (TEM) to observe UFBs in the nutrient solutions used in a crop-growing system known as a plant factory. In this factory, TEM images taken from various points in the supply line indicate that the concentration of UFBs in the nutrient solution is conserved, starting from their addition to the nutrient solution in the buffer tank, through the peat-moss layer, all the way to the rhizosphere. Measurements also show that a thin film formed on the surface of UFBs in the nutrient solution, with greater film thickness at the rhizosphere. This film is considered to be made from the accumulation of impurities coming from solute and the peat-moss layer.

Highlights

Recent attention has been given to industrial application of ultra-fine bubbles, or UFBs, which are bubbles of diameter below 1 μm
UFBs of about 300 nm in diameter were found to exist at an average number density of 4 × 108/mL
UFBs were measured in the control solution, a solution made with tap water without the UFB generator, and found to have about half the total number of UFBs

Summary

Introduction

Recent attention has been given to industrial application of ultra-fine bubbles, or UFBs, which are bubbles of diameter below 1 μm. In agriculture, UFB-added solution has been tested as a growth promoter. In one such test, Ebina et al [1] showed that the growth of hydroponically cultivated Brassica campestris over four weeks was significantly promoted in air-UFB-added water compared to that with normal water. Liu et al [4] showed that the germination rate of barley seeds was significantly increased by O2-UFB-added water. These studies have shown that the growth of plants can be promoted by using UFB-added water.

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