What is the appropriate content of HCO3− irrigated into tomato cultivation soil for enhancing its carbon fixation?

To improve the carbon fixation capacity of crops, ${\mathrm{HCO}}_3^{-}$ is applied to the rhizosphere under a suitable pH value, which can enhance the utilization of CO₂ by crops. This study aimed to clarify the maximum fixation capacity of ${\mathrm{HCO}}_3^{-}$ in tomato plants by exploring the optimal concentration of ${\mathrm{HCO}}_3^{-}$ in their cultivation environment. The results showed that the tomato could maintain both the net increase of ${\mathrm{HCO}}_3^{-}$ fixation and normal growth, when the maximum concentration of ${\mathrm{HCO}}_3^{-}$ in the cultivation surroundings was discovered during the growth period: 25 mmol/L NaHCO₃-solution in seed germination, 14 g-NaHCO₃/kg-soil in the cotyledon development, 8 to 10 g-NaHCO₃/kg-soil during the seedling, 6 g-NaHCO₃/kg-soil in the flowering, and 9 g-NaHCO₃/kg-soil in the fruiting. However, excessive ${\mathrm{HCO}}_3^{-}$ could impair the development of tomato plants, especially the vegetative growth at seedling/flowering stages and the root growth at fruiting stage due to the increased soil pH and EC by ${\mathrm{HCO}}_3^{-}$. On the other hand, H${}_2$O produced by the decomposition of ${\mathrm{HCO}}_3^{-}$ by tomato plants could alleviate physiological stress under severe conditions. Therefore, ${\mathrm{HCO}}_3^{-}$ became the main inorganic carbon source of tomato assimilation under extreme stress. This study provides a data basis for selecting and optimizing the appropriate ${\mathrm{HCO}}_3^{-}$ application amount when CO₂ is used for agricultural eco-fixation in the form of ${\mathrm{HCO}}_3^{-}$ in the future.