Salinity is a serious limiting factor for the growth of rhizobia. Some rhizobia are tolerant to salt stress and promote plant growth, but the mechanisms underlying these effects are poorly characterized. The growth responses and osmoprotectants in four Bradyrhizobium strains were examined under salt stress in this study. Two-dimensional electrophoresis (2-DE) and mass spectrometry were conducted to investigate protein profiles in rhizobia exposed to salt stress. Subsequently, salt tolerance in stylo (Stylosanthes guianensis) inoculated with rhizobia was further detected in hydroponics. Results showed that the Bradyrhizobium strain RJS9-2 exhibited higher salt tolerance than the other three Bradyrhizobium strains. RJS9-2 was able to grow at 0.35 M NaCl treatment, while the other three Bradyrhizobium strains did not grow at 0.1 M NaCl treatment. Salt stress induced IAA production, and accumulation of proline, betaine, ectoine, and trehalose was observed in RJS9-2 but not in PN13-1. Proteomics analysis identified 14 proteins regulated by salt stress in RJS9-2 that were mainly related to the ABC transporter, stress response, and protein metabolism. Furthermore, under saline conditions, the nodule number, plant dry weight, and N concentration in stylo plants inoculated with RJS9-2 were higher than those in plants inoculated with PN13-1. These results suggest that the tolerance of RJS9-2 to salt stress may be achieved by the coordination of indole-3-acetic acid (IAA) production, osmoprotectant accumulation, and protein expression, thus promoting stylo growth.

The application of green manure is a common way to increase the soil’s level of total organic carbon (TOC) and its fractions. However, the amount of green manure to apply and how the combined application of phosphate fertilizer affects the movement of TOC, and of its fractions, is still unclear. We conducted a column experiment with two treatments of phosphate fertilizer (with and without) and green manure (0, low amount level, high amount level). The longitudinal movement distance and accumulation amount of each organic carbon fraction were investigated after 14 days and 28 days. The results indicated that green manure, phosphate fertilizer, and incubation time affected the movement of the soil organic carbon fractions by affecting the initial quality of the green manure (TOC, cellulose, and lignin content), as well as the changes in quality. Green manure significantly increased the accumulation amount of the organic carbon fractions in the soil, and the high-level input of green manure increased the movement distance and accumulation amount of the organic carbon fractions; phosphorus fertilizer did not have a significant effect on the movement distance of the organic carbon fractions, but it did significantly affect accumulation amount. The 28-day incubation period increased the movement distance and the accumulation amount of the organic carbon fractions, with the exception of the particulate organic carbon (POC), compared to the 14-day incubation period. Taken together, these findings suggest that the high-level of input of green manure combined with the application of P fertilizer is beneficial for increasing the movement of the organic carbon fractions to the depth of the soil, and promotes their accumulation, which is an important agronomic management strategy for improving soil acidity in tropical regions.

The primary challenges in fruit and vegetable preservation include extending storage duration while preserving sensory quality and nutritional value. In this study, sesbania gum (SG) was oxidized to prepare oxidized sesbania gum (OSG). An OSG/ZnO composite film was subsequently prepared, combining OSG, sodium carboxymethyl cellulose (CMC), and nano-zinc oxide (nano-ZnO). The preparation technology was determined via a response surface optimization experiment. When the addition amount of nano-ZnO exceeded 0.3 mg/mL, the composite films exhibited an antibacterial rate of over 90% against E. coli and S. aureus. For wampee (Clausena lansium (Lour.) Skeels) preservation, a OSG/ZnO-0.3 film was directly applied as a coating. The findings demonstrated favorable results in terms of the rate of rotting, soluble solids, and titrable acidity, effectively prolonging wampee fruit storage. This suggests the potential of an OSG composite film with nano-ZnO as a promising fruit packaging material, thereby expanding the application of SG and wampee fruit preservation.

Intercropping green manure (GM) may be a good solution to the problems of acid soil in tropical plantations. Soil organic nitrogen (No) may change due to the application of GM. A three-year field experiment was conducted to determine the effect of different utilization patterns of Stylosanthes guianensis GM on soil No fractions in a coconut plantation. Three treatments were set: no GM intercropping (CK), intercropping and mulching utilization pattern (MUP), and intercropping and green manuring utilization pattern (GMUP). The content dynamics of soil total N (TN) and soil No fractions including of non-hydrolysable N (NHNo) and hydrolyzable N (HN) in the cultivated soil layer was examined. The results showed that after three years of intercropping, the TN content of the MUP and GMUP treatment was 29.4% and 58.1% respectively higher (P < 0.05) than those of the initial soil, and the No fractions content of GMUP and MUP treatment was 15.1%-60.0% and 32.7%-111.0% higher (P < 0.05) than those of the initial soil. The further results indicated that after three years of intercropping, compared with CK, GMUP and MUP could increase the content of TN by 32.6% and 61.7% respectively, and No fractions content was also increased by 15.2%-67.3% and 32.3%-120.3%% respectively (P < 0.05). The No fractions content of GMUP treatment was 10.3%-36.0% higher than those of MUP treatment (P < 0.05). These results indicated that intercropping Stylosanthes guianensis GM could significantly increase the soil N including of the TN an No fractions content, and the GMUP was more effective than MUP, therefore, GMUP is a better GM utilization pattern to improve the soil fertility and should be popularized in the tropical fruit plantation.

The application of green manure (GM), particularly leguminous varieties, demonstrates significant benefits for crop cultivation in acidic soils by enhancing the soil organic nitrogen (No) pool. To maximize these agronomic advantages, it is crucial to implement scientifically grounded application strategies. To this end, an incubation experiment was conducted to investigate the content, movement distance, and accumulation of acidic soil organic N (No) at different distances from the GM application microsite. Stylosanthes GM (10 or 40 ton/ha) was applied with or without phosphate fertilizer (monocalcium phosphate, MCP) at 44 kg/ha P, placed on the surface of soil cylinders. The GM/fertilizer and soil were incubated for 14 and 28 d. The results indicated the total organic nitrogen (TNo) content—including both non-acid-hydrolyzable N (NAHNo) and acid-hydrolyzable N (AHNo) fractions—significantly (p < 0.05) increased at the GM microsite after GM application. The influence of GM generally weakened as the distance from the site increased, and the spatial impact range exhibited significant modulation by three key parameters: incubation period, GM rates, and MCP addition. Subsequent analysis revealed a positive correlation between GM rate/incubation period and the movement distance of No fractions at GM microsite, demonstrating rate-dependent temporal dynamics. They were also increased by the addition of MCP after a longer incubation period but inhibited after a shorter period. This information will improve the efficiency of GM use, with or without MCP addition, and decrease the environmental load due to N pollution caused by GM.

In this study, sesbania gum (SG) was successfully modified by using H₂O₂ as the oxidant, CuSO₄ as the catalyst, and octenyl succinic anhydride as the esterification agent. The effects of oxidation and esterification on the structure and properties of SG were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), among other techniques. By FTIR analysis it was found that the oxidation did not introduce new groups, while the ester carbonyl group was successfully introduced into the molecular chain of SG. The oxidation of SG by H₂O₂ involves the cleavage of long chains, which is also the main cause of its reduction in viscosity. Oxidation reduced the crystallinity of SG, and its crystal structure was found to be severely damaged after esterification. Both oxidation and esterification altered the thermal properties of SG, whereby the thermal stability and freeze-thaw stability of the modified SG were improved and the expansion capacity was effectively reduced.