Effects of water and fertilizer optimization on rhizosphere priming and regenerating capacity of perennial rice

As the ratoon season progresses in perennial rice, strengthening rhizosphere regulation during late growth is important for improving the soil micro-ecological environment, preventing stubble-related continuous-cropping constraints, and sustaining high and stable yields in perennial systems. Here, we used Yunda 25 (YD25) and conducted a pot experiment with three water and fertilizer regimes applied at the ratoon tillering stage: flooded irrigation without seedling-boost fertilizer (S), alternate wetting and drying without seedling-boost fertilizer (G), and alternate wetting and drying with seedling-boost fertilizer (GF). We assessed the effects of these regimes on ratoon-season yield, rhizosphere soil enzyme activities, and microbial functional diversity.The water–fertilizer treatments significantly affected rhizosphere redox potential and soil enzyme activities. Compared with S, GF and G significantly increased polyphenol oxidase, peroxidase, urease, and sucrase by 36.17%–39.01%, 5.56%–18.23%, 30.92%–56.83%, and 38.11%–64.16%, respectively. Ratoon-season yield increased by 34.47%–36.69% under GF and by 19.51%–22.23% under G. Microbial functional diversity in carbon-source metabolism also differed significantly among treatments. Relative to S, GF and G increased substrate utilization of amino acids, polymers, amines, carboxylic acids, and carbohydrates by 34.40%–39.23%, 67.62%–69.92%, 63.10%–75.56%, 18.48%–42.71%, and 53.53%–66.72%, respectively.Chessboard scores and correlation analyses further indicated that water and fertilizer coupling promoted positive feedbacks in the rhizosphere micro-ecosystem and increased the relative abundance of beneficial functional genera, including Bacillus, Pseudomonas, Burkholderia, Streptomyces, and Nitrosospira. These changes improved soil micro-ecological conditions and enhanced nitrogen cycling, as indicated by higher expression and mineralization related to ammonia-oxidation genes amoA (AOA) and amoA (AOB), nitrate-reduction gene narG, and denitrification genes nirK, nirS, and nosZ. As a result, rhizosphere nutrient activation and effective nutrient supply increased, root vigor improved, and plants achieved faster early growth and higher yield. Overall, alternate wetting and drying combined with seedling-boost fertilizer (GF) showed the strongest regulating effect during the ratoon season.