Endogenous salicylic acid maintains photosynthetic performance and redox balance to support short-term cadmium stress tolerance in <i>Monochoria korsakowii</i>

was exposed to 0.1 or 0.3 mM Cd for six days and foliar-sprayed with SA biosynthesis inhibitors (2-aminoindane-2-phosphonic acid and 1-aminobenzotriazole) to elucidate endogenous SA functions under short-term Cd stress. The results showed that Cd stress reduced total chlorophyll content, the net photosynthetic rate, and the performance index on an absorption basis. The upregulation of specific antioxidant enzymes and non-enzymatic antioxidants contributed to limiting malondialdehyde accumulation. Lastly, Cd stress enhanced the activities of benzoic acid 2-hydroxylase (BA2H) and phenylalanine ammonia-lyase (PAL), two key enzymes involved in SA biosynthesis. However, SA inhibitors reversed the Cd-induced upregulation of PAL and BA2H activities and aggravated the Cd-induced decline in photosynthetic performance. Furthermore, compared with the corresponding Cd treatments, SA inhibitors, reduced antioxidant enzyme activities and proline levels, and exacerbated Cd-induced malondialdehyde accumulation. Finally, SA inhibitors significantly increased the levels of phytochelatins and non-protein thiols. These results indicate that SA is a critical endogenous signal for enhancing plant Cd tolerance, which lays a theoretical foundation for developing phytohormone-based phytoremediation strategies.