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.

Soilless cultivation technology is a key means of overcoming traditional agricultural resource limits, providing an important path to efficient and sustainable modern agriculture by precisely regulating crop rhizospheric environments. This paper systematically reviews the technical system of soilless cultivation, nutrient solution management strategies, the interaction mechanism of rhizosphere microorganisms, and future development directions, aiming to reveal its technical advantages and innovation potential. This review shows that solid and non-solid substrate cultivation improves resource utilization efficiency and yield, but substrate sustainability and technical cost need urgent attention. The dynamic regulation of nutrient solution and intelligent management can significantly enhance nutrient absorption efficiency. Rhizosphere microorganisms directly regulate crop health through nitrogen fixation, phosphorus solubilization, and pathogen antagonism. However, the community structure and functional stability of rhizosphere microorganisms in organic systems are prone to imbalance, requiring targeted optimization via synthetic biology methods. Future research should focus on the development of environmentally friendly substrates, the construction of intelligent environmental control systems, and microbiome engineering to promote the expansion of soilless cultivation towards low-carbon, precise, and spatial directions. This paper systematically references the theoretical improvements and practical innovations in soilless cultivation technology, facilitating its large-scale application in food security, ecological protection, and resource recycling.

Aeration is considered beneficial for hydroponics. However, little information is available on the effects of aeration, and even less on solutions that use bubble flow and their agronomic effects. In this study, the effects of aeration intensity on plants were studied through cultivation experiments and flow field visualization. It was found that the growth of plants did not increase linearly with an increase in aeration intensity. From the results of this study, when the aeration intensity was within the low range (0.07–0.15 L·L⁻¹ NS·min⁻¹), increasing the aeration intensity increased the plant growth. However, after the aeration intensity reached a certain extent (0.15–1.18 L·L⁻¹ NS·min⁻¹), some indicators did not change significantly. When the aeration intensity continued to increase (1.18–2.35 L·L⁻¹ NS·min⁻¹), growth began to decrease. These results show that for increasing dissolved oxygen and promoting plant growth, the rule is not “the higher the aeration intensity, the better”. There is a reasonable range of aeration intensity within which crops grow normally and rapidly. In addition, increasing the aeration intensity means increasing energy utilization and operating costs. In actual hydroponics production, it is very important to find a reasonable aeration intensity range.

Unlike in soil culture, a substrate (nutrient solution) in a hydroponics system can flow, and this can affect both nutrient uptake and plant growth. In this study, we hydroponically cultivated Swiss chard (Beta vulgaris L. ssp. cicla) under different flow rates to analyze changes in the growth, nutrient uptake, and nutrient use efficiency. When the flow rate was intensified from 2 to 4 L/min, leaf area, the fresh weight, dry weight, and root length increased. However, when the flow rate was increased from 4 to 8 L/min, values of these growth parameters decreased. The nutrient uptake had a similar trend relative to the growth parameters and nutrient use efficiency of macronutrient elements, increased as the flow rate increased. This indicates that the flow rate affects plant growth by influencing the nutrient uptake, and an increase in the flow rate can aid in improving nutrient use efficiency. In hydroponics, regulating the flow rate at a reasonable volume is recommended to increase yield by enhancing nutrient use efficiency, but too intensive a flow rate may cause excessive physical stimulation to plants and inhibit their growth. Therefore, it is important to choose an appropriate substrate flow rate for optimal hydroponics production.

The principal difference between hydroponics and other substrate cultivation methods is the flowing liquid hydroponic cultivation substrate. Our previous studies have revealed that a suitable flowing environment of nutrient solution promoted root development and plant growth, while an excess flow environment was unfavorable for plants. To explain the thigmomorphogenetic response of excess flow-induced metabolic changes, six groups of lettuce (Lactuca sativa L.), including two flow conditions and three time periods, were grown. Compared with the plants without flow, the plants with flow showed decreased root fresh weight, total root length, root surface area, and root volume but increased average root diameter and root density. The roots with flow had more upregulated metabolites than those without flow, suggesting that the flow may trigger metabolic synthesis and activity. Seventy-nine common differential metabolites among six groups were screened, and enrichment analysis showed the most significant enrichment in the arginine biosynthesis pathway. Arginine was present in all the groups and exhibited greater concentrations in roots with flow than without flow. It can be speculated from the results that a high-flowing environment of nutrient solution promotes arginine synthesis, resulting in changes in root morphology. The findings provide insights on root thigmomorphogenesis affected by its growing conditions and help understand how plants respond to environmental mechanical forces.