Synergistic effects of biochar and organic fertilizer on root exudates, microbial community, and yield in dry direct-seeded rice

Dry direct-seeded rice (DDSR) offers significant water-saving potential but often suffers from unstable yields, low nutrient-use efficiency, and disrupted root-soil-microbe interactions under alternating wet-dry cycles. Although biochar and organic fertilizers have been widely reported to improve soil quality and microbial function, their synergistic effects on DDSR root exudates, microorganisms, and crops require further investigation. Therefore, we conducted a field experiment with six treatments integrating biochar application (0, 5, and 10 t/hm²) and organic fertilizer substitution (0 % or 20 % fertilizer N) to investigate their synergistic regulation of root exudates, microbial communities, and yield. The findings revealed that the root exudative capacity of DDSR was enhanced (metabolites of B1N2 up 17, down 9 and B2N2 up 9, down 6) by the synergistic effect of biochar and organic fertilizer. Random forest modeling identified lipids and lipid-like molecules and organic acids and derivatives as the most critical metabolome between treatments under biochar and organic fertilizer application. Over-Representation Analysis (ORA) revealed that arginine and proline, glycine, serine, threonine, and glycerophospholipid were the key regulatory pathways of biochar and organic fertilizer. Secondly, stochastic processes dominated the assembly process of soil microorganisms, and root exudates and soil physicochemical properties under biochar and organic fertilizers combined to promote mutual shifts in soil microbial community assembly drivers, which altered soil microbial community diversity. Notably, the microbial community-root exudates-soil physicochemical property interactions under the effect of biochar and organic fertilizers were dominated by synergistic effects and supplemented by antagonistic effects, which together promoted the root development of dry direct-seeded rice and significantly increased rice yield (3.96–11.64 %). In conclusion, the results of the study confirmed the feasibility of stable and high rice yield and microecological regulation in dry direct-seeded paddy fields by regulating key root exudates and microbial diversity.