Sapium sebiferum (L.) Roxb. is an economically important tree in eastern Asia, and it exhibits many traits associated with good forestation species in coastal land. However, scarce research has been conducted to elucidate the effects of rhizosphere bacterial diversity on the adaptability and viability of S. sebiferum trees grown in the coastal environment. Field trials were conducted, and rhizosphere soil samples were collected from typical coastal and forestry nursery environments. Rhizosphere bacterial communities were evaluated using 16S rRNA pyrosequencing. A total of 43 bacterial phyla were detected in all the coastal and nursery rhizospheric soil samples. Relatively higher rhizosphere community diversity was found in coastal field-grown trees. Proteobacteria, Acidobacteriota, Bacteroidota, Chloroflex, and Gemmatimonadota were dominant bacterial phyla in rhizosphere communities of tallow trees. However, the rare groups in the coastal rhizosphere soils, with a relative abundance lower than 1%, including Latescibacterota, Methylomirabilota, NB1-j, and Nitrospirota, were largely absent in the nursery field-grown tree’s rhizosphere soils. LEfSe analysis identified a total of 43 bacterial groups that were more significantly abundant in the coastal rhizosphere environment than in that of forestry nursery grown trees. Further, our cladogram analysis identified Nitrospirota, Methylomirabilota, NB1-j, and Latescibacterota as biomarkers for the coastal environment at the phylum taxonomic level. These results suggested that the adaptability of S. sebiferum trees in coastal environment might be promoted by rhizosphere microbial interactions. Complex tree–microbe interactions might enhance the resistance of the trees to coastal environment, partially by recruiting certain bacterial microbiome species, which is of high saline-alkali resistance.

The water lily (Nymphaea tetragona) is an ancient angiosperm that belongs to the Nymphaeaceae family. As a rooted floating-leaf plant, water lilies are generally cultivated in fresh water, therefore, little is known about their survival strategies under salt stress. Long-term salt stress causes morphological changes, such as the rapid regeneration of floating leaves and a significant decrease in leaf number and surface area. We demonstrate that salt stress induces toxicity soon after treatment, but plants can adapt by regenerating floating leaves that are photosynthetically active. Transcriptome profiling revealed that ion binding was one of the most-enriched GO terms in leaf-petiole systems under salt stress. Sodium-transporter-related genes were downregulated, whereas K⁺ transporter genes were both up- and downregulated. These results suggest that restricting intracellular Na⁺ importing while maintaining balanced K⁺ homeostasis is an adaptive strategy for tolerating long-term salt stress. ICP-MS analysis identified the petioles and leaves as Na-hyperaccumulators, with a maximum content of over 80 g kg⁻¹ DW under salt stress. Mapping of the Na-hyperaccumulation trait onto the phylogenetic relationships revealed that water lily plants might have a long evolutionary history from ancient marine plants, or may have undergone historical ecological events from salt to fresh water. Ammonium transporter genes involved in nitrogen metabolism were downregulated, whereas NO₃⁻-related transporters were upregulated in both the leaves and petioles, suggesting a selective bias toward NO₃⁻ uptake under salt stress. The morphological changes we observed may be due to the reduced expression of genes related to auxin signal transduction. In conclusion, the floating leaves and submerged petioles of the water lily use a series of adaptive strategies to survive salt stress. These include the absorption and transport of ions and nutrients from the surrounding environments, and the ability to hyperaccumulate Na⁺. These adaptations may serve as the physiological basis for salt tolerance in water lily plants.

Water lilies (Nymphaea L.) are ancient angiosperms that can be cultivated in both fresh and brackish water. Water lily plants have adapted morphologically and physiologically to the aqueous environment. Nonetheless, little is known about the regulatory mechanisms that enable water lily to acclimate to saline conditions, restricting its production and distribution. To illustrate the role of roots in water lily salinity tolerance, we investigated the adaptive regulation of the water lily root system under high salinity. Aspects of its root architecture, including root length, surface area, volume, and tip number, were significantly reduced by salt stress. Transcriptome sequencing showed that 120 genes were upregulated and 1214 genes were downregulated under salt stress. The differentially expressed genes were mainly enriched in oxidoreductase activity, structural molecule activity, and transmembrane transporter activity. Most ion transporter genes were downregulated, suggesting that water lily may partially close ion channels and/or transporters to avoid excessive ion accumulation or ion imbalance under long-term salt stress. Genes related to NO₃⁻ transport were both up- and downregulated, whereas genes related to ammonium transport were uniformly downregulated, suggesting that transcriptional changes may play a role in balancing nitrogen metabolism under long-term saline conditions. The roots showed relatively high concentrations of Na⁺ and had the ability to hyper-accumulate Na⁺ under salt stress. These findings provide insight into the regulatory mechanisms that enable water lily roots to tolerate salinity and lay a foundation for the breeding of salt-tolerant cultivars.