Natural deep eutectic solvents (NADESs) coupled with microwave-assisted extraction (MAE) were applied to extract total flavonoid compounds from spent sweet potato (Ipomoea batatas L.) leaves. In this study, ten different NADESs were successfully synthesized for the MAE. Based on single-factor experiments, the response surface methodology (RSM) was applied, and the microwave power, extraction temperature, extraction time, and solid–liquid ratio were further evaluated in order to optimize the yields of total flavonoid compounds. Besides, the extracts were recovered by macroporous resin for the biological activity detection of flavonoid compounds. As a result, NADES-2, synthesized by choline chloride and malic acid (molar ratio 1:2), exhibited the highest extraction yield. After that, the NADES-2-based MAE process was optimized and the optimal conditions were as follows: microwave power of 470 W, extraction temperature of 54 °C, extraction time of 21 min, and solid–liquid ratio of 70 mg/mL. The extraction yield (40.21 ± 0.23 mg rutin equivalents/g sweet potato leaves) of the model validation experiment was demonstrated to be in accordance with the predicted value (40.49 mg rutin equivalents/g sweet potato leaves). In addition, flavonoid compounds were efficiently recovered from NADES-extracts with a high recovery yield (>85%) using AB-8 macroporous resin. The bioactivity experiments in vitro confirmed that total flavonoid compounds had good DPPH and O₂⁻· radical-scavenging activity, as well as inhibitory effects on E. coli, S. aureus, E. carotovora, and B. subtilis. In conclusion, this study provides a green and efficient method to extract flavonoid compounds from spent sweet potato leaves, providing technical support for the development and utilization of sweet potato leaves’ waste.

Beneficial microorganisms are an effective approach to ameliorate degraded soils and improve farmland productivity. At present, systematic research on the regulatory effects of plant growth-promoting bacteria on tomato growth in acidic soils is still lacking. In this study, pot experiments combined with microbiome technology were conducted to investigate the effects of Bacillus cereus BC-101, Bacillus methylotrophicus BM-25 and Bacillus amyloliquefaciens BA-11 on the growth of tomato seedlings and the structure of rhizosphere microbial communities in acidic soils. All the three tested plant growth-promoting bacteria significantly promoted the growth of tomato seedlings. The plant heights were increased by 43.01%, 94.38% and 99.20% under BC, BM and BA treatments, respectively. Meanwhile, the bacterial inoculation significantly increased plant biomass, improved leaf photosynthetic pigment contents, activated protective enzyme activities, and elevated the contents of osmotic adjustment substances and growth-promoting hormones. In addition, the bacteria could improve the physicochemical properties of acidic soils, enhance soil enzyme activities, and significantly increase the relative abundances of beneficial genera such as Pseudomonas and Bacillus in the rhizosphere. Rhizospheric inoculation of the three plant growth-promoting bacteria improved tomato growth and enhanced rhizosphere soil properties under naturally acidic soil conditions, suggesting their potential application in the biological improvement of acidic soils. This study provides practical evidence for the comprehensive improvement and application of acidic soils.