Soil microbial nitrate (NO₃⁻) immobilization plays a vital role in enhancing the nitrogen (N) retention in the subtropical montane agricultural landscapes. However, how and why the potential microbial NO₃⁻ immobilization and the relative contribution of fungi and bacteria vary across different land use types remain still unclear in the subtropical mosaic montane agricultural landscapes. Thus, in the present study, soil gross microbial NO₃⁻ immobilization rates as well as the respective contribution of fungi and bacteria were determined throughout the whole soil profiles for three land use types (woodland, orchard, and cropland) by using the ¹⁵N tracing and amino sugar–based stable isotope probing (Amino sugars-SIP) techniques. The soil gross microbial NO₃⁻ immobilization rates in woodland soils were significantly higher than those in cropland and orchard soils across different soil layers (p < 0.05), and those of topsoil were significantly higher than those for subsoils (e.g., 20–40 cm) across different land use types (p < 0.05). Soil microbial biomass C (MBC) and N (MBN), organic C (SOC), total N (TN), and dissolved organic C (DOC) contents and C/N ratios were closely associated to gross microbial NO₃⁻ immobilization rates. Fungi played a greater role than bacteria in immobilizing soil NO₃⁻ in woodland and orchard soils, but the opposite occurred in cropland soils that over 85% of the variations in fungal and bacterial NO₃⁻ immobilization rates could be explained by their respective phospholipid fatty acid–derived (PLFA-derived) biomass. The present study indicated that afforestation may be effective to enhance soil NO₃⁻ retention in alkaline soils, thereby likely decreasing the risk of NO₃⁻ losses in subtropical mosaic montane agricultural landscapes through enhancing the soil NO₃⁻ immobilization by both fungi and bacteria.

土壤微生物硝酸盐（NO ₃ ^-）固定对于增强亚热带山地农业景观中氮（N）的保留起着至关重要的作用。然而，在亚热带马赛克山地农业景观中，潜在的微生物NO ₃ ^-固定以及真菌和细菌的相对贡献在不同土地利用类型中如何以及为何存在差异仍不清楚。因此，在本研究中，^通过使用₁₅ ^N示踪和基于氨基糖的稳定同位素探测（氨基糖-SIP）技术。不同土层林地土壤总微生物NO ₃ ^-固定率均显着高于农田和果园土壤（p  < 0.05），表土显着高于下层土（如20~40 cm）。 ）跨越不同的土地利用类型（p  < 0.05）。_{土壤微生物生物量C (MBC)和N (MBN)、有机C (SOC)、总N (TN)和溶解有机C (DOC)含量和C/N比与总微生物NO 3} ^-固定率密切相关。在林地和果园土壤中，真菌在固定土壤 NO ₃ ^-方面发挥着比细菌更大的作用，但在农田土壤中则相反，超过 85% 的真菌和细菌 NO ₃ ^-固定率变化可以通过各自的磷脂脂肪来解释酸衍生（PLFA 衍生）生物质。本研究表明，植树造林可能有效增强碱性土壤中 NO ₃ ^{- 的}保留，从而可能通过增强真菌和细菌对土壤 NO 3 - 的固定_来^降低亚热带镶嵌山地农业景观中 NO 3 - 损失_的^风险。