Green manure and soil conditioner improve soil properties, regulates microbial communities, and increase yields and quality of Uncaria rhynchophylla

Uncaria rhynchophylla is an important traditional herbal medicine in China, and the yield and quality of Uncaria rhynchophylla can be improved by suitable soil conditioners with green manure because of changing the soil properties. In this paper, Uncaria rhynchophylla associated alkaloid and soil microbial community were investigated. The field experiment was set up with the following control group: (M1, no soil conditioner) and different soil conditioner treatment groups (M2, biomass ash; M3, water retention agent; M4, biochar; M5, lime powder and M6, malic acid). The results showed that M2 significantly increased the fresh and dry weight and the contents of isorhynchophylline, corynoxeine, isocorynoxeine and total alkaloids. Acidobacteria, Proteobacteria, Actinobacteria and Chloroflexi were major bacterial phyla. Correlation analysis showed that fresh and dry weight was significantly positively correlated with Acidobacteria phylum, while alkali-hydrolyzable nitrogen, phosphatase activity, fresh and dry weight, corynoxeine and isocorynoxeine were significantly negatively correlated with Chloroflexi phylum. The application of soil conditioner M2 increased the abundance of Acidobacteria phylum and decreased the abundance of Chloroflexi phylum, which contributed to improving the soil nutrient content, yield and quality of Uncaria rhynchophylla. In summary, biomass ash may be a better choice of soil conditioner in Uncaria rhynchophylla growing areas.