Understanding the Morpho-Anatomical, Physiological, and Functional Response of Sweet Basil to Isosmotic Nitrate to Chloride Ratios

Sweet basil (Ocimum basilicum L.) is a leafy green with a short-production cycle that is emerging as a model species among aromatic plants. Modulating the mineral composition of the nutrient solution has proved to be a valuable tool to uncover the mechanisms and responses that higher plants adopt in relation to the availability of mineral nutrients. The aim of this work was to examine the effects on basil of four isosmotic nutrient solutions with different nitrate to chloride ratios. These two anions share uptake and transport mechanisms in plants and are often considered antagonist. To this goal, we analyzed morpho-anatomical and physiological parameters as well as quality-related traits, such as the antioxidant capacity, the leaf color, the mineral composition, and the aromatic profile in relation to the nutrient ratios. Moreover, using a full factorial design, we analyzed leaves in two consecutive harvests. The data indicated a broad, multifaceted plant response to the different nutritional ratios, with almost all the recorded parameters involved. Overall, the effects on basil can be explained by considering an interdependent combination of the nitrate and chloride roles in plant nutrition and physiology. Our work revealed the extent of the modification that can be achieved in basil through the modification of the nutrient solution. It also provided indications for more nutrient efficient growing conditions, because a moderate increase in chloride limits the expected negative impact of a sub-optimal nitrate fertilization.