Straw return plays an important role in improving soil fertility and crop yield. Straw combined with nitrogen (N) fertilizer can alleviate soil nutrient stress caused by N competition between soil microorganisms and crops during straw decomposition. Nevertheless, the microbial mechanisms by which N application regulates the allocation of straw-derived carbon (C) and N in soil–plant systems remain unresolved. In this study, we explored microbial roles in straw nutrient release and transfer under N fertilization using a pot wheat experiment with four treatments (i.e., no straw and no N fertilizer, S0N0; N fertilizer alone, S0N1; C/N double-labeled maize straw alone, S1N0; and C/N double-labeled maize straw plus N fertilizer, S1N1). We found that S1N1 significantly increased wheat above-ground biomass, by 16.69–43.82%, compared with the other treatments. Soil mineral N contents (NO-N and NH-N) in S1N1 gradually decreased over time, whereas more abundant soil microbial biomass N (MBN) and dissolved organic N (DON) were detected at the later stage of wheat growth. This result, which suggested a persistent N supply potential under straw return accompanied by N fertilization, was supported by evidence that the transfer of straw N to plants in S1N1 was 1.92 times higher than that in S1N0. Moreover, S1N1 strongly stimulated the proliferation of soil Actinobacteria, Proteobacteria, and Ascomycota and increased microbial network complexity. Five bacterial biomarkers (, , , , and ) and two fungal biomarkers ( and ) were detected in S1N1 at the early stage, whereas biomarkers newly abundant in the late stage of S1N1 were more diverse. According to functional prediction analysis, these S1N1-induced microbiota were associated with cellulolysis, chitinolysis, and N-cycling. Partial least squares path modeling revealed that N fertilization-induced regulation of the distribution of straw-derived C and N was mainly through the bacterial community, not the fungal community. Overall, these results suggested that chemical N fertilization promoted the release of straw-derived N and their transfer to crops by regulating microbial community composition, metabolic functions, and microbial biomass turnover.

中文翻译：

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施氮肥下微生物在增强秸秆氮向小麦转移中的作用

秸秆还田对于提高土壤肥力、提高农作物产量具有重要作用。秸秆配施氮肥可缓解秸秆分解过程中土壤微生物与作物氮竞争造成的土壤养分胁迫。然而，施氮调节土壤-植物系统中秸秆来源的碳（C）和氮的分配的微生物机制仍未解决。在本研究中，我们通过盆栽小麦试验，采用四种处理（即无秸秆且无氮肥，S0N0；仅施氮肥，S0N1；C/N 双标记玉米），探讨了氮肥下微生物在秸秆养分释放和转移中的作用。单独秸秆，S1N0；C/N 双标记玉米秸秆加氮肥，S1N1）。我们发现，与其他处理相比，S1N1 显着增加了小麦地上生物量，增加了 16.69-43.82%。S1N1土壤矿物质氮含量（NO-N和NH-N）随着时间的推移逐渐下降，而在小麦生长后期检测到更丰富的土壤微生物量N（MBN）和溶解性有机氮（DON）。这一结果表明，在秸秆还田并施氮的情况下，具有持续的氮供应潜力，并得到了证据的支持，即S1N1中秸秆氮向植物的转移是S1N0中的1.92倍。此外，S1N1强烈刺激土壤放线菌、变形菌和子囊菌的增殖，并增加微生物网络的复杂性。在S1N1早期阶段检测到5种细菌生物标志物（、、、、和）和两种真菌生物标志物（和），而在S1N1后期新丰富的生物标志物更加多样化。根据功能预测分析，这些 S1N1 诱导的微生物群与纤维素分解、几丁质分解和氮循环相关。偏最小二乘路径模型表明，施氮引起的秸秆来源碳和氮分布的调节主要是通过细菌群落，而不是真菌群落。总体而言，这些结果表明，化学施氮肥通过调节微生物群落组成、代谢功能和微生物生物量周转，促进秸秆来源的氮的释放及其向作物的转移。