Effects of fertilization regimes on active microbial groups in photosynthetic carbon utilization

• MNPK and NPK treatments significantly increased the net 13 C incorporation into plant-soil system. • MNPK fertilization enhanced fungal assimilation and raised F:B ratio in later C decomposition. • M fertilizer reduced photosynthetic C in PLFAs but enhanced its incorporation into G- bacteria. Fertilization is an essential management method to maintain and increase soil carbon (C) in agroecosystems, while the role of soil microbes in rhizodeposited C utilization remains largely unknown. We conducted in-situ 13 CO 2 pulse labeling to track the newly fixed photosynthetic 13 C from maize ( Zea mays L.) to soil and rhizodeposited C utilization by soil microbes under five-year of fertilization regimes, including no fertilizer as a control (CK), organic fertilizer (M), inorganic fertilizer (NPK), and organic–inorganic fertilizer (MNPK), respectively. We measured the 13 C incorporated into plant, soil and phospholipid fatty acids ( 13 C-PLFAs) on days 1, 7, and 21 after labeling to determine the 13 C partitioning in the plant-soil system and utilized by different microbial groups. The findings indicated that MNPK and NPK treatments significantly increased the net 13 C incorporation into shoots, roots, and soil compared to CK and M treatments, due to larger biomass, higher available phosphorus, and nitrate nitrogen. The MNPK treatment significantly enhanced fungal 13 C assimilation (particularly in the 18:2ω6c biomarker), increasing the fungi-to-bacteria (F:B) ratio over sampling time. MNPK showed a higher F:B ratio than NPK on day 21, with total soil 13 C retention positively correlating with this ratio in later stages. The CK treatment exhibited greater 13 C assimilation in PLFA on day 1, suggesting more active initial photosynthetic C utilization of microbes. M fertilizer application decreased the 13 C-PLFA, while increasing the 13 C incorporated in G- bacteria during photosynthetic C utilization. Our findings clarify the functional partitioning of rhizodeposited C utilization among distinct microbial guilds, revealing that organic–inorganic fertilization promotes fungal-mediated processes during late decomposition. These insights advance the understanding of microbial-mediated C cycling under different fertilization regimes.