Salinity is not only a threat to organisms and ecosystems, but also a major factor restricting the development of agricultural production. This study aimed to explore the modification effect of in-situ Jerusalem artichoke (genotype NY-1) cultivation on the rhizosphere micro-ecological environment in the saline-alkali region along the southeast coast of China. We analyzed the change of carbon and nitrogen in the saline soil from a microbial perspective, through the quantification of the area of root channels, rhizosphere secretions and soil microbiome (cbbL, cbbM and nifH). The root channels of NY-1 not only improved the physical structure of saline soil, but also provided a living space for microorganisms, afforded basic conditions for the optimization of the soil micro-ecological environment. In addition, rhizosphere secretions (from roots of NY-1 as well as microorganisms), such as carbohydrates, hydrocarbons, acids, etc., could be considered as a way to improve the saline-alkali soil habitat. NY-1 increased the diversity and abundance of autotrophic and nitrogen-fixing bacteria in saline soil (rhizosphere > bulk soils), which should be a biological way to increase the amount of carbon and nitrogen fixation in soil. Moreover, some of the detected genera (Sideroxydans, Thiobacillus, Sulfuritalea, Desulfuromonas, etc.) participate in the carbon and nitrogen cycles, and in the biogeochemical cycle of other elements. In short, Jerusalem artichoke can improve not only the physical and chemical properties of saline-alkali soil, but also promote material circulation and energy flow in the micro-ecological rhizosphere environment of saline soils.
Quinoa (Chenopodium quinoa), a herbaceous annual, has been widely cultivated in recent years because of its high nutritional value and strong tolerance to abiotic stresses. The study was conducted at two planting densities (LD, 10 plants/m2; HD, 65 plants/m2) on ameliorated coastal mudflats in Jiangsu Province, China (118° 46′ E, 32° 03′ N). The results showed soil salinity and organic matter were higher in the HD than LD treatment, and salinity of the rhizosphere soil was higher than that of the non-rhizosphere soil. Quinoa grown in HD was taller, with thicker stalks and lower yields per plant, but higher yield per unit area. Amplicon sequencing showed that Proteobacteria, Bacteroidota and Acidobacteria were the dominant bacterial phyla. Regarding the rhizosphere soil, the Shannon index was higher in the HD than LD, and Proteobacteria and Bacteroidota were more abundant in the HD treatment. Fifty-one differential metabolites were identified by metabolomic assays, belonging to 14 annotated metabolic pathways. S-adenosylmethionine was the most abundant and up-regulated metabolite (fold change >1.67), and was more abundant in the roots from the LD than HD treatment. Docosahexaenoic acid was more abundant in the HD than LD treatment, and was down-regulated metabolite. In conclusion, planting density was an important factor affecting quinoa yield; compared with unplanted soil, planting quinoa at low density increased the content of the important metabolite S-adenosylmethionine in the root system of quinoa, and high density cultivation of quinoa increased soil salinity and microbial abundance and diversity.
Soil salinization is a serious problem leading to ecological degradation. Melia azedarach is highly salt-tolerant, and its application to saline-alkali land is a promising strategy for restoring degraded lands. In this study, we analyzed the soil properties and metabolome of M. azedarach roots grown in low- (< 3 g/kg; L), medium- (5~8 g/kg; M), and high- (> 10 g/kg; H) salinity soils to explore the amelioration effect and adaptation mechanism of M. azedarach to soils with differential salinity. Cultivation of M. azedarach was associated with a decrease in the concentration of Na and increases in organic matter content and alkaline phosphatase and urease activities in the rhizosphere soil. The metabolome analysis revealed that a total of 382 (ESI+) and 277 (ESI-) differential metabolites (DEMs) were detected. The number of DEMs in roots rose with increased soil salinity, such as sugars and flavonoids in H vs. L, and amino acids in M vs. L. The most up-regulated DEMs were 13-S-hydroxyoctadecadienoic acid, 2’-Deoxyuridine and 20-hydroxyleukotriene B4. Combined analysis of soil properties and M. azedarach DEMs indicated that alkaline phosphatase activity was positively correlated with traumatic acid concentration. Taken together, these results indicate that M. azedarach has the potential to reduce soil salinity and enhance soil enzyme activity, and it can adapt to salt stress by regulating metabolites like sugars, amino acids, and flavonoids . This study provided a basis for understanding the mechanism underlying the adaptation of M. azedarach to saline-alkali soil and its amelioration.
Soil salinization leading to ecological degradation and Melia azedarach can be effective in improving soil characteristics, such as reducing soil salinity. However, the mechanisms underlying the adaptation of Melia azedarach to saline-alkali land are unknown. In this study, we analyzed the soil properties and metabolome of Melia azedarach roots grown in high-salt (11.5 g/kg), medium-salt (7.5 g/kg), and low-salt soils (0.37 g/kg) to explore the mechanisms of adaptation of Melia azedarach to salt stress. Soil Na was decreased, while soil organic matter, alkaline phosphatase and urease activities were increased when Melia azedarach was planted in low-, medium- and high- saline alkali soil. The metabolome analysis showed that the number of differential metabolites (DEMs), especially the up-regulated DEMs rose with the soil salinity increased. The sugar, amino acid and flavonoid DEMs produced by Melia azedarach were mostly up-regulated with the increase of soil salinity. The results demonstrated Melia azedarach was able to alleviate saline stress and reduce soil salinity. We propose that in situ bioremediation with Melia azedarach could be considered to ameliorate the coastal saline-alkali soil.
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