Biostimulants and their role in improving the nutrition of plants in hydroponic conditions

Consumers are increasingly appreciating the production of high quality, healthy fruits and vegetables, especially when they are obtained through activities with minimal impact on the environment. New approaches have been proposed to increase the sustainability of agricultural productions and improve the quality of crops and crop-derived products. A promising tool is the use of biostimulants in the form of mixtures of substances and/or microorganisms. The application of these products to plants leads to positive metabolic changes. For these reasons, the development of new biostimulants are in focus of scientific interest. Among their different roles, biostimulants influence plant growth and metabolism, especially because of their content in signaling molecules. A significant increase in root hair length and density is often observed in plants treated with biostimulants, suggesting that these substances induce a “nutrient acquisition response” that favours nutrient uptake in plants via an increase in the absorptive surface area. Unfortunately, the physiological mechanisms underlying plant-biostimulant interactions remain partially unknown. In this context, hydroponic cultivation systems (i.e., substrate culture, nutritional film technique, floating system) are the most effective in evidencing the biostimulant effects, thanks to the precise control of plant nutrition that permit the modulation of bioactive compounds. Vegetable production under hydroponic cultivation seems to be an efficient tool for increasing phytochemicals and/or beneficial nutrients in plants as well as for controlling anti-nutrients accumulation such as nitrates.