High-throughput absolute quantification sequencing reveals that high organic fertiliser use increased bacterial abundance and metabolic function in reddish paddy soil

Rational application of organic and chemical fertilizers is beneficial to improve crop yield and quality. However, the effect of combining these fertilizers on bacterial community structure and metabolic functions remains unclear, especially in reddish paddy soil. In the present study, absolute quantification 16S rRNA amplicon sequencing technology (AQS) was used to study the responses of soil bacterial community composition and its absolute abundance to environmental factors under different application ratios of organic and chemical fertilisers for two consecutive years in reddish paddy soil. The results showed that replacing the chemical fertiliser with organic fertiliser significantly increased the total nitrogen (TN), total potassium, hydrolysed nitrogen, and soil organic carbon (SOC), and significantly decreased the soil bulk density. These effects were more prominent in the treatment with 60% of organic fertilizer (60M). More importantly, AQS revealed that different fertilization treatments non-significantly affected soil bacterial diversity (Shannon) and richness (Chao1) but significantly changed the composition and abundance of bacterial communities. SOC, TN, and available potassium were the key factors shaping bacterial community structure under different fertilization regimes. The bacterial absolute abundance in the 60M treatment was 25.30% and 56.58% higher than that in the NPK and 30M treatments, respectively. Functional prediction analysis with PICRUSt2 revealed that the 60M treatment increased the abundance of species involved in xenobiotic biodegradation and metabolism, amino acid metabolism, and lipid metabolism, and further improved metabolic functions to a certain degree.