Crop production under hydroponic environments has many advantages, yet the effects of solution flow rate on plant growth remain unclear. We conducted a hydroponic cultivation study using different flow rates under light-emitting diode lighting to investigate plant growth, nutrient uptake, and root morphology under different flow rates. Swiss chard plants were grown hydroponically under four nutrient solution flow rates (2 L/min, 4 L/min, 6 L/min, and 8 L/min). After 21 days, harvested plants were analyzed for root and shoot fresh weight, root and shoot dry weight, root morphology, and root cellulose and hemicellulose content. We found that suitable flow rates, acting as a eustress, gave the roots appropriate mechanical stimulation to promote root growth, absorb more nutrients, and increase overall plant growth. Conversely, excess flow rates acted as a distress that caused the roots to become compact and inhibited root surface area and root growth. Excess flow rate thereby resulted in a lower root surface area that translated to reduced nutrient ion absorption and poorer plant growth compared with plans cultured under a suitable flow rate. Our results indicate that regulating flow rate can regulate plant thigmomorphogenesis and nutrient uptake, ultimately affecting hydroponic crop quality.

In hydroponics, the flow pattern of nutrient solution in a cultivation container affects the growth of plants. Even if the flow rate of nutrient solution is the same between containers, the flow pattern may differ based on the size and shape of the containers. Therefore, the flow pattern cannot be comprehensively described by flow rate alone. In order to identify the relationship between plant growth, root morphology, nutrient uptake, and flow pattern, a hydroponic cultivation of Swiss chard was carried out. In addition, in order to describe the flow pattern in a specific cultivation container, hydroponic flow patterns were observed via flow field visualization using particle image velocimetry. As a result, with the increase in flow rate, it was found that a specific flow rate can form an ideal flow pattern for plant growth. Under this flow pattern, nutrient absorption is promoted and roots are elongated, thereby absorbing more nutrients and further promoting plant growth. However, when the flow rate exceeds the ideal value, plant growth is hindered. In summary, identifying the ideal nutrient solution flow pattern in hydroponics can facilitate better crop production.