Abstract. Nitrogen (N) fertilization has received worldwide attention due to its benefits with regard to soil fertility and productivity, but excess N application also causes an array of ecosystem degenerations, such as greenhouse gas emissions. Generally, soil microorganisms are considered to be involved in upholding a variety of soil functions. However, the linkages between soil cropland properties and microbial traits under different N fertilizer application rates remain uncertain. To address this, a 4-year in situ field experiment was conducted in a meadow soil from the Northeast China Plain after straw return with the following treatments combined with regular phosphorus (P) and potassium (K) fertilization: (i) regular N fertilizer (N + PK), (ii) 25 % N fertilizer reduction (0.75N + PK), (iii) 50 % N fertilizer reduction (0.5N + PK), and (IV) no N fertilizer (PK). Cropland properties and microbial traits responded distinctly to the different N fertilizer rates. Treatment 0.75N + PK had overall positive effects on soil fertility, productivity, straw decomposition, and microbial abundance and functioning and alleviated greenhouse effects. Specifically, no significant difference was observed in soil organic carbon (SOC), total N, P content, straw C, N release amounts, microbial biomass C, N content, and cellulase and N-acetyl-D-glucosaminidase activities, which were all significantly higher than in 0.5N + PK and PK. Greenhouse gas emissions was reduced with the decreasing N input levels. Moreover, the highest straw biomass and yield were measured in 0.75N + PK, which were significantly higher than in 0.5N + PK and PK. Meanwhile, 0.75N + PK up-regulated aboveground biomass and soil C:N and thus increased the abundance of genes encoding cellulose-degrading enzymes, which may imply the potential ability of C and N turnover. In addition, most observed changes in cropland properties were strongly associated with microbial modules and keystone taxa. The Lasiosphaeriaceae within the module-1 community showed significant positive correlations with straw degradation rate and C and N release, while the Terrimonas within the module-3 community showed a significant positive correlation with production, which was conducive to soil multifunctionality. Therefore, our results suggest that straw return with 25 % chemical N fertilizer reduction is optimal for achieving soil functions. This study highlights the importance of abiotic and biotic factors in soil health and supports green agricultural development by optimizing N fertilizer rates in meadow soil after straw return.

中文翻译：

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适度减氮和秸秆还田调节草甸土壤中的农田功能和微生物特性


摘要。氮 （N） 施肥因其在土壤肥力和生产力方面的好处而受到全世界的关注，但过量施用氮肥也会导致一系列生态系统退化，例如温室气体排放。通常，土壤微生物被认为参与维持各种土壤功能。然而，不同施氮量下土壤农田性质与微生物性状之间的联系仍不确定。为了解决这个问题，在秸秆还田后，在东北平原的草甸土壤中进行了为期 4 年的原位田间试验，采用以下处理并结合常规磷 （P） 和钾 （K） 施肥：（i） 常规氮肥 （N + PK），（ii） 25 % 氮肥减少 （0.75N + PK），（iii） 50 % 氮肥减少 （0.5N + PK）， （IV） 不使用氮肥 （PK）。农田性质和微生物性状对不同的氮肥用量有明显的响应。0.75N + PK 处理对土壤肥力、生产力、秸秆分解、微生物丰度和功能具有总体积极影响，并减轻了温室效应。具体而言，土壤有机碳 （SOC） 、全 N、P 含量、秸秆 C、N 释放量、微生物生物量 C、N 含量、纤维素酶和 N-乙酰-D-氨基葡萄糖苷酶活性均显著高于 0.5N + PK 和 PK，温室气体排放量随 N 输入水平的降低而减少。此外，在 0.75N + PK 中测得的秸秆生物量和产量最高，显著高于 0.5N + PK 和 PK。同时，0.75N + PK 上调地上生物量和土壤 C：N，从而增加了编码纤维素降解酶的基因的丰度，这可能意味着 C 和 N 周转的潜在能力。此外，大多数观察到的农田特性变化与微生物模块和关键分类群密切相关。模块-1 群落内的 Lasiosphaeriaceae 与秸秆降解速率和 C 和 N 释放呈显著正相关，而模块-3 群落内的 Terrimonas 与生产呈显著正相关，有利于土壤多功能性。因此，我们的结果表明，减少 25 % 化学氮肥的秸秆还田是实现土壤功能的最佳选择。本研究强调了非生物和生物因素对土壤健康的重要性，并通过优化秸秆还田后草甸土壤中的氮肥用量来支持绿色农业发展。