Nitraria sibirica Pall., a typical halophyte that can survive under extreme drought conditions and in saline-alkali environments, exhibits strong salt tolerance and environmental adaptability. Understanding the mechanism of molecular and physiological metabolic response to salt stress of plant will better promote the cultivation and use of halophytes. To explore the mechanism of molecular and physiological metabolic of N. sibirica response to salt stress, two-month-old seedlings were treated with 0, 100, and 400 mM NaCl. The results showed that the differentially expressed genes between 100 and 400 mmol L⁻¹ NaCl and unsalted treatment showed significant enrichment in GO terms such as binding, cell wall, extemal encapsulating structure, extracellular region and nucleotide binding. KEGG enrichment analysis found that NaCl treatment had a significant effect on the metabolic pathways in N. sibirica leaves, which mainly including plant-pathogen interaction, amino acid metabolism of the beta alanine, arginine, proline and glycine metabolism, carbon metabolism of glycolysis, gluconeogenesis, galactose, starch and sucrose metabolism, plant hormone signal transduction and spliceosome. Metabolomics analysis found that the differential metabolites between the unsalted treatment and the NaCl treatment are mainly amino acids (proline, aspartic acid, methionine, etc.), organic acids (oxaloacetic acid, fumaric acid, nicotinic acid, etc.) and polyhydric alcohols (inositol, ribitol, etc.), etc. KEGG annotation and enrichment analysis showed that 100 mmol L⁻¹ NaCl treatment had a greater effect on the sulfur metabolism, cysteine and methionine metabolism in N. sibirica leaves, while various amino acid metabolism, TCA cycle, photosynthetic carbon fixation and sulfur metabolism and other metabolic pathways have been significantly affected by 400 mmol L⁻¹ NaCl treatment. Correlation analysis of differential genes in transcriptome and differential metabolites in metabolome have found that the genes of AMY2, BAM1, GPAT3, ASP1, CML38 and RPL4 and the metabolites of L-cysteine, proline, 4-aminobutyric acid and oxaloacetate played an important role in N. sibirica salt tolerance control. This is a further improvement of the salt tolerance mechanism of N. sibirica, and it will provide a theoretical basis and technical support for treatment of saline-alkali soil and the cultivation of halophytes.

Background: As an important epigenetic mark, 5-methylcytosine (5mC) methylation is involved in many DNA-dependent biological processes and plays a role during development and differentiation of multicellular organisms. However, there is still a lack of knowledge about the dynamic aspects and the roles of global 5mC methylation in wood formation in tree trunks. In this study, we not only scrutinized single-base resolution methylomes of primary stems (PS), transitional stems (TS), and secondary stems (SS) of Populus trichocarpa using a high-throughput bisulfite sequencing technique, but also analyzed the effects of 5mC methylation on the expression of genes involved in wood formation. Results: The overall average percentages of CG, CHG, and CHH methylation in poplar stems were ~ 53.6%, ~ 37.7%, and ~ 8.5%, respectively, and the differences of 5mC in genome-wide CG/CHG/CHH contexts among PS, TS, and SS were statistically significant (p < 0.05). The evident differences in CG, CHG, and CHH methylation contexts among 2 kb proximal promoters, gene bodies, and 2 kb downstream regions were observed among PS, TS, and SS. Further analysis revealed a perceptible global correlation between 5mC methylation levels of gene bodies and transcript levels but failed to reveal a correlation between 5mC methylation levels of proximal promoter regions and transcript levels. We identified 653 and 858 DMGs and 4978 and 4780 DEGs in PS vs TS and TS vs SS comparisons, respectively. Only 113 genes of 653 DMGs and 4978 DEGs, and 114 genes of 858 DMGs and 4780 DEG were common. Counterparts of some of these common genes in other species, including Arabidopsis thaliana, are known to be involved in secondary cell wall biosynthesis and hormone signaling. This indicates that methylation may directly modulate wood formation genes and indirectly attune hormone signaling genes, which in turn impact wood formation. Conclusions: DNA methylation only marginally affects pathway genes or regulators involved in wood formation, suggesting that further studies of wood formation should lean towards the indirect effects of methylation. The information and data we provide here will be instrumental for understanding the roles of methylation in wood formation in tree species.

Plant salt tolerance relies on a coordinated functioning of different tissues and organs. Salinity tissue tolerance is one of the key traits that confers plant adaptation to saline environment. This trait implies maintenance low cytosolic Na⁺/K⁺ ratio in metabolically active cellular compartments. In this study, we used Nitraria sibirica Pall., a perennial woody halophytes species, to understand the mechanistic basis of its salinity tissue tolerance. The results showed that the growth of seedlings was stimulated by 100-200 mM NaCl treatment. The ions distribution analysis showed that the leaves acted as Na⁺ sink while plant root possess superior K⁺ retention. The excessive Na⁺ absorbed from soil was mainly transported to the shoot and eventually sequestrated into mesophyll vacuoles in the leaves. As a result, N. sibirica could keep optimal balance of K⁺/Na⁺ at a tissue- and cell-specific level under saline condition. To enable this, N. sibirica increased both vacuolar H⁺-ATPase and H⁺-PPase enzymes activities and up-regulated expressions of NsVHA, NsVP1 and NsNHX1 genes. Vacuolar Na⁺ sequestration in the leaf mesophyll mediated by NsVHA, NsVP1 and NsNHX1 reduced the Na⁺ concentration in cytosol and inhibited further K⁺ loss. Meanwhile, N.sibirica enhanced the TPK expression at the transcriptional level to promote K⁺ efflux from vacuole into cytoplasm, assisting in maintaining cytosolic K⁺ homeostasis. It is concluded that the tissue tolerance traits such as vacuolar Na⁺ sequestration and intracellular K⁺ homeostasis is critical to confer adaptation of N. sibirica to soil salinity.

Elaeagnus angustifolia is one of the most extensively afforested tree species in environment-harsh regions of northern China. Despite its exceptional tolerance to saline soil, the intrinsic adaptive physiology has not been revealed. In this study, we investigated the growth, organ-level ionic relations and organic osmoregulation of the seedlings hydroponically treated with 0, 100 and 200 mM NaCl for 30 days. We found that the growth characteristics and the whole-plant dry weight were not obviously stunted, but instead, were even slightly stimulated by the treatment of 100 mM NaCl. In contrast, these traits were significantly inhibited by 200 mM NaCl treatment. Interestingly, as compared with the control (0 mM NaCl), both 100 and 200 mM NaCl treatments had a promotional effect on root growth as evidenced by 26.3% and 2.4% increases in root dry weight, respectively. Roots had the highest Na⁺ and Cl^- concentrations and obviously served as the sink for the net increased Na⁺ and Cl^-, while, stems might maintain the capacity of effective Na⁺ constraint, resulting in reduced Na⁺ transport to the leaves. K⁺, Ca²⁺ and Mg²⁺ concentrations in three plant organs of NaCl-treated seedlings presented a substantial decline, eventually leading to an enormously drop of K⁺/Na⁺ ratio. As the salt concentration increased, proline and soluble protein contents continuously exhibited a prominent and a relatively tardy accumulation, respectively, whereas soluble sugar firstly fell to a significant level and then regained to a level that is close to that of the control. Taken together, our results provided quantitative measures that revealed some robust adaptive physiological mechanisms underpinning E. angustifolia’s moderately high salt tolerance, and those mechanisms comprise scalable capacity for root Na⁺ and Cl^- storage, effectively constrained transportation of Na⁺ from stems to leaves, root compensatory growth, as well as an immediate and prominent leaf proline accumulation.

Using Non-invasive Micro-test Technology (NMT), the Na⁺, K⁺ and H⁺ flux profiles in the root meristem regions were investigated in Nitraria sibirica Pall. seedlings under different NaCl concentrations. NaCl stress increased the K⁺ and Na⁺ contents in the roots of N. sibirica seedlings. NaCl stress significantly increased the steady Na⁺ efflux from the N. sibirica seedling roots. Steady K⁺ effluxes were measured in the control roots (without NaCl) and in the roots treated with 200 mM NaCl, and no significant differences were observed between the two treatments. The steady K⁺ efflux from roots treated with 400 mM NaCl decreased gradually. NaCl treatment significantly increased the H⁺ influx. Pharmacological experiments showed that amiloride and sodium vanadate significantly inhibited the Na⁺ efflux and H⁺ influx, suggesting that the Na⁺ efflux was mediated by a Na⁺/H⁺ antiporter using energy provided by plasma membrane H⁺-ATPase. The NaCl-induced root K⁺ efflux was inhibited by the K⁺ channel inhibitor tetraethylammonium chloride (TEA), and was significantly increased by the H⁺-ATPase inhibitor sodium vanadate. The NaCl-induced K⁺ efflux was mediated by depolarization-activated outward-rectifying K⁺ channels and nonselective cation channels (NSCCs). Under salt stress, N. sibirica seedlings showed increased Na⁺ efflux due to increased plasma membrane H⁺-ATPase and Na⁺/H⁺ antiporter activity. High H⁺ pump activity not only restricts the Na⁺ influx through NSCCs, but also limits K⁺ leakage through outward-rectifying K⁺ channels and NSCCs, leading to maintenance of the K⁺/Na⁺ balance and higher salt tolerance.

In this study, the effects of biochar and compost on the amelioration of coastal saline soil were investigated through indoor leaching experiments and soil culture experiments. The results revealed that the multivoid structure of biochar and compost, when applied to soil, effectively improved soil hydraulic conductivity, promoted the leaching of salt ions, and reduced soil electrical conductivity. Owing to the high pH value of biochar and the lower pH value of compost, the combined application of the two has a complementary effect on improving the pH value of coastal saline soils. The calcium (Ca²⁺) and magnesium (Mg²⁺) contained in biochar and compost are exchanged with Na⁺ adsorbed by soil colloids, which reduces the sodium (Na⁺) adsorption ratio (SAR) value of the soil. Biochar and compost improve the physical properties of the soil, and the organic matter they contain helps soil particles aggregate with each other and form stable clusters, thus promoting the formation of soil agglomerates, which are conducive to the formation of clusters with a diameter of ≤0.25 mm. Biochar and compost are rich in nutrients, and their application significantly increased the contents of available nutrients and organic matter as well as the activities of urease, phosphatase, and dehydrogenase in saline soils. However, too high of an application rate of biochar increases the soil pH value, and excessive application of compost can lead to greater soil conductivity, which inhibits the activities of soil urease, phosphatase and dehydrogenase. Therefore, rational control of application rates is essential for improving coastal saline soils. Future research should further explore the synergistic effects of biochar and compost in improving soil structure, nutrient effectiveness, and microbial activity to promote their effective application in coastal saline–alkaline soil improvement.