Ultrafine bubbles effectively enhance soybean seedling growth under nutrient deficit stress

Abstract

Ultrafine bubbles (UFBs) exhibit a number of unique physical characteristics; however, reports on plant growth enhancement by UFB application are controversial. Here, we report experiments conducted to test whether UFB technology effectively promotes plant growth. We analyzed the effects of three experimental factors: water (UFB addition), hypoxia (aeration), and fluid movement (stirring) on the growth of soybean seedlings cultured hydroponically under low and high nutrition levels in a controlled environment room under artificial lighting for 8 days. When no nutrients were supplied, positive UFB water effects were evident, but low nutrition reduced UFB water-mediated growth enhancement and high nutrition totally obliterated any growth enhancement by UFB water. We concluded that UFB water-induced growth enhancement was effective and significant under nutrient deficit stress but no growth enhancement was observed, and even negative effects were evident, under favorable plant growth conditions.

Promotive or suppressive effects of ultrafine bubbles on crop growth depended on bubble concentration and crop species

“…First, shoot growth promotion under zero-nutrition (Figure 3 (a)) occurred in all six species tested. This is consistent with previous research results (Iijima et al, 2020). A clearly defined interspecific difference was observed in the UFB concentration effects.…”

“…species tested, consistent with our previous research (Iijima et al, 2020). In soybean shoot growth, UFB even showed statistically suppressive effect in the low level UFB concentration, which supports the result of tomato grown in air UFB (Armed et al, 2018).…”

“…The solution was replaced every two days. As observed in our previous study (Iijima et al, 2020), UFB treatment did not affect pH, electrical conductivity (EC), and dissolved oxygen (DO) during seedling growth. Pre-germination was done at 30°C in the dark for 28, 30, 48, 28, 30, and 48 hours for wheat, rice, maize, soybean, cowpea, and adzuki bean, respectively, as identified by preliminary trials.…”

“…This short-term experiment was performed using the same conditions described in our previous report (Iijima et al, 2020). Briefly, plants were grown in different levels of Hoagland solution in a plant growth room at 28/23°C day/night temperature, under 14 h photoperiod and 318 ± 2 µmol m −2 s −1 of photosynthetically active radiation (PAR) at the top canopy level.…”

“…Therefore, it is necessary to clarify the growth conditions that always promote the growth of major crop species by UFB application. In our previous report on UFB effects on plant growth, the environmental conditions of the water culture such as nutrient levels, fluid movement, and aeration effects were investigated (Iijima et al, 2020). The results clearly showed that the growth promotion of young soybean seedling (8 days after germination) was remarkable under nutrient stress when cultured using a deionized water medium with UFB.…”