https://www.jstage.jst.go.jp/article/ecb/60/4/60_195/_article
Previous studies have reported that ultrafine bubbles (UFBs) can promote
plant growth. However, the optimum application of UFBs has not been
sufficiently clarified yet. In this study, we investigated the optimum UFB
content index for lettuce cultivation. Content index (CI) was defined as
the product of the pass numbers (Pn) and dilution ratio (D) and taken
to be indicative of UFB density; where Pn was the number of times water
was passed through the UFB generator. UFB treatment comprised three
different Pn: 10 passes (P1), 25 passes (P2), and 100 passes (P3). Six UFB
treatments were conducted for each Pn in six D treatments as: control,
UFB 10%, UFB 30%, UFB 50%, UFB 75%, and UFB 100%. The results confirmed
that there was an appropriate level of CI to accelerate the growth of lettuce
in a hydroponic solution, that is, a UFB CI of 7.5―30 and 18.75―30 in the
nursery and cultivation stages, respectively. However, lettuce growth was
significantly smaller on CI of 100. In addition, DPPH and NBT tests were
conducted to measure the total antioxidant capacity (TAC) and superoxide
radical on lettuce. TAC and superoxide radical accumulation were influenced by
the UFB content index
Lettuce growth was significantly influenced by the
UFB content in the nutrition solutions of the experiment.
In this study, UFB content index was defined the product
of Pn and D which was indicative UFB density in nutrient
solution. UFB contents of 7.5―30 and 18.75―30 were
observed to promote lettuce growth in nursery and cultivation
stages, respectively. A previous study reported that
UFB density was positively correlated with the extent of
exogenous ROS generation, which in UFB treatment
involves the hydroxyl radical (OH). It could stimulate the
accumulation of superoxide radicals in leaf lettuce which
led to observed promotional or inhibitory effects of UFB
on lettuce growth. An appropriate level of UFB content
index in the nutrient solution can enhance lettuce growth.
However, high UFB content index can inhibit lettuce
growth. In addition, TAC appeared to be significantly influenced
by different UFB treatments. The quantitative measurement of
exogenous and endogenous ROS production
should be further investigated to determine its effect on
plant growth in more detail
