An Energy-Rich Phosphate Compound Enhances the Growth of Lettuce Through the Activation of Photosynthesis, Growth, and Induced Systemic Resistance–Related Processes

The large inputs of chemical fertilizer in protected vegetable cultivation have caused lower plant nutrient use efficiency and soil secondary salinization. The current trend is to seek a biotype foliar fertilizer and explore its growth-promoting mechanism. Calcium fructose-1,6-diphosphate (FB), an energy-rich phosphate compound, was evaluated for growth, photosynthesis, nutrient uptake, and systemic resistance to salt in lettuce (Lactuca sativa L.) seedlings cultivated in a greenhouse. FB-mediated transcriptional regulation was examined by RNA sequencing. Metabolic activity of the rhizosphere microbial community was evaluated using Biolog™ ECO plates, and the effect of FB on biofilm formation by plant growth–promoting rhizobacteria (PGPR) was measured using the crystal violet assay. FB had a remarkable benefit in promoting plant growth by biomass accumulation, leaf net photosynthesis improvement, and absorption of P and K while enhancing salt resistance through antioxidant enzyme activation and decreasing Na⁺/K⁺ ratio in roots. FB induced a genotype-dependent response pattern, including an increase in gene expression of photosynthesis, Ca²⁺ channel protein, and lignin synthesis, and a decrease in the expression of defense response genes. Moreover, FB enhanced the metabolic activity of the original rhizosphere microbial community under non-saline conditions and had a positive effect on biofilm formation and swimming motilities of PGPR. FB promotes lettuce growth by inducing photosynthesis enhancement, nutrient absorption, and systemic resistance activation. In addition, it provides new insights into the relationship between plants and soils.