Salicylic acid alleviates tidal flooding and salinity toxicity on Barringtonia racemosa seedlings by activating the stress defense mechanism

The tidal flooding and salinity stress caused by global warming and rising sea level challenge the survival of mangrove wetland plants. Salicylic acid (SA) is an important endogenous signaling molecule that enhances the ability of plants to tolerate abiotic stress by regulating growth, physiological and metabolic processes. Consider that the semi-mangrove plant Barringtonia racemosa (L.) Spreng is already listed as endangered because of habitat degradation. In this study, exogenous hormone SA was sprayed on the leaf surface to regulate the tolerance of B. racemosa to the tidal flooding and salinity stress. Results revealed that SA application (0.5-1.5 mmol L-1) considerably altered morpho-growth indices (leaf and root morphology and total biomass) in plants through increasing key substance that balances the osmotic potential including proline content and leaf soluble protein content, photosynthetic indexes (chlorophyll a, b and total chlorophyll, chlorophyll stability index) and secondary metabolic substance (total phenolic content (TPhe) and flavonoid content). The utilization of correlation analysis, membership function evaluation and principal component analysis, encompassing all 20 variables, yielded valuable insights into the categorization of salt-tolerant treatments according to their reaction to SA. Specifically, the application of SA spray has been found to enhance the concentration of TPhe, thereby significantly or even remarkably modulating the positive impact of the 50% index. The most effective outcome in terms of alleviating tidal flooding and salinity stress (15 and 16.5 parts per thousand) was observed when SA was administered at a concentration of 1.0 and 1.5 mmol L-1. These results suggest SA (1.0 and 1.5 mmol L-1) could be used as an effective, economic, easily available and safe phenolic agent against tidal flooding and salinity stress in B. racemosa.