Small molecular organic acid potassium promotes rice (Oryza sativa L.) photosynthesis by regulating CBC and TCA cycle

Small molecular organic acids have been found to stimulate plant growth. However, limitition has investigated whether these acids combined with potassium (K) would be more effective in promoting plants growth and photosynthesis than chemical fertilizer KCl. In this experiment, rice ( Oryza sativa . L) seedlings were subjected to four treatments K-deficiency (CK), KCl (IOS), HCOOK (OSA), and CH 3 COOK (OSB) and photosynthesis and growth parameters were examined. The results indicated that K played a significant role in photosynthesis and growth of rice seedlings, while OSA and OSB exhibited more pronounced effects on promoting photosynthesis and growth. Moreover, the total contents of total N and total K, as well as the RuBisCO enzyme activity were higher in OSA and OSB than those in IOS. The small molecule organic acid potassium also altered the morphology of stomata, rendering it more conducive to photosynthesis. KCl reduced the relative contents of malate, citrate, isocitrate, fumarate, glutarate, and pyruvate in the tricarboxylic acid cycle (TCA cycle), which were negatively correlated with stomatal conductance. Compared with KCl, small molecule organic acids further reduced the relative contents of metabolites in the TCA cycle, and increased the relative content of 3-PGA in the Calvin-Benson cycle (carbon fixation pathway) by enhancing RuBisCO enzyme activity and upregulating photosynthetic-related gene expression. Thus, the mechanism underlying the enhanced photosynthesis by small molecule organic potassium was attributed to its promotion of K absorption, which in turn improves stomatal conductance and enhances carbon fixation capacity. This study has practical implications for increasing rice yield through the application of small molecular organic acid potassium.