Straw return is a widespread agricultural practice for improving cropland nitrogen (N) stocks. However, the contribution of microbial N to the soil aggregate N pool and the underlying microbial metabolic regulation mechanisms remain uncertain. This study was based on a 13-year field experiment with rice ( L.) and wheat ( L.) rotation, using only a chemical fertilizer alone (CF) as the control. We analyzed the effects of the chemical fertilizer combined with (CS, 9500 kg ha y) and wheat (4000 kg ha y) straw on microbial derived-N, microbial carbon (C) and N limitations. We also assessed microbial N use efficiency (NUE) in various aggregates of ferric lixisols (020 cm). Rotary tillage reached a depth of 20 cm. The CS significantly increased microbial-derived N concentrations in soil aggregates and enhanced the contribution of fungal residual N to the N pool in aggregates < 0.25 mm, but did not affect those > 0.25 mm. Conversely, the bacterial contribution to the N pool was not affected by CS. Meanwhile, CS significantly increased the soil organic C and microbial biomass in the aggregates. The results of our eco-enzymatic stoichiometric model revealed that the CS significantly alleviated microbial C limitations and increased microbial NUE in soil aggregates. Structural equation modeling further revealed that the microbial biomass and soil organic C contents are key drivers of the microbial C limitation. The increased contribution of fungal residual N to the N pools in < aggregates 0.25 mm was attributed to improved microbial NUE resulting from the straw, without altering net N mineralization rates or β-1,4-N-acetylglucosidase activity. Our findings suggest that straw return promotes microbial-derived N production and sequestration by alleviating microbial C limitation. The strategies governing these microbial-derived N responses in aggregates to straw return might vary. This might be valuable for designing cropland management practices to improve N storage.

中文翻译：

---

长期秸秆还田增加了真菌残留对土壤微团聚氮库的贡献：生态酶化学计量研究


秸秆还田是改善农田氮（N）储量的一种广泛的农业做法。然而，微生物氮对土壤团聚氮库的贡献以及潜在的微生物代谢调节机制仍不确定。这项研究基于为期 13 年的水稻 (L.) 和小麦 (L.) 轮作田间试验，仅使用化肥 (CF) 作为对照。我们分析了化肥与（CS，9500 kg ha y）和小麦（4000 kg ha y）秸秆混施对微生物源氮、微生物碳（C）和氮限制的影响。我们还评估了各种铁水溶土（020 cm）聚集体中的微生物氮利用效率（NUE）。旋耕深度达到20厘米。 CS显着增加了土壤团聚体中微生物来源的氮浓度，并增强了< 0.25 mm团聚体中真菌残留氮对氮库的贡献，但不影响> 0.25 mm团聚体中的氮库。相反，细菌对氮库的贡献不受CS的影响。同时，CS显着增加了土壤有机碳和团聚体中的微生物量。我们的生态酶化学计量模型的结果表明，CS 显着缓解了微生物碳的限制并增加了土壤团聚体中的微生物 NUE。结构方程模型进一步揭示，微生物生物量和土壤有机碳含量是微生物碳限制的关键驱动因素。真菌残留氮对 0.25 mm < 聚集体中氮库的贡献增加，归因于秸秆产生的微生物 NUE 的改善，而不改变净氮矿化率或 β-1,4-N-乙酰葡萄糖苷酶活性。 我们的研究结果表明，秸秆还田可以通过缓解微生物碳限制来促进微生物源氮的产生和固存。控制这些微生物源氮对秸秆还田的聚集体反应的策略可能会有所不同。这对于设计农田管理实践以改善氮储存可能很有价值。