地表覆盖和施氮对黄土高原塿土团聚体尺度碳氮转化的影响

Evaluating soil C and N transformations in aggregate is crucial for elucidating the development of soil quality under different agricultural practices. The coupled application of soil surface mulching and N fertilization prevails in the Loess Plateau because of its beneficial effects on reducing irrigation and enhancing crop yield. However, the information about their impacts on soil C/N transformation remains limited. Contradictory results were also reported for soil C/N transformation in response to N fertilization and plastic film/straw mulching, and the limited studies were scarcely conducted in soil aggregate. Thus, the present study is conducted on a 15-year field experiment associated with mulching and N fertilization in Lou soil of the Loess Plateau, and aims to examine soil C and N distribution and humus structure in different particle-size aggregates, and determine soil microbiological characteristics including soil extracellular enzymes and functional microorganisms involved in soil C and N cycling. The results will be conducive to exploring the characteristics and the underlying mechanism of C and N cycling in Lou soil affected by long-term soil surface mulching and N fertilization, and thus provide a new theory for optimizing agricultural management in the Loess Plateau.

团聚体尺度碳氮转化特征研究对揭示不同农田管理措施下土壤质量演变规律至关重要。覆盖施肥作为黄土高原典型的节水增产模式，其对土壤碳氮转化影响的研究仍比较薄弱；不同覆盖模式（如地膜、秸秆）及施氮下土壤碳氮响应特征亦是报道各异，且相关研究尚未深入到团聚体水平。因此，本项目以黄土高原长达15年的塿土节水培肥定位试验为平台，从土壤团聚体水平，系统研究土壤碳氮分布与腐殖质结构变化特点、碳氮转化相关胞外酶作用规律以及碳氮转化相关功能微生物响应特征，旨在揭示长期地表覆盖和施氮下土壤碳氮转化特征及潜在作用机制，为优化黄土高原农田管理提供新的科学依据。

地表覆盖和施氮是提高旱区作物产量的主要措施。本文基于黄土高原2003年开始的覆盖施氮定位试验，研究长期覆盖（无覆盖，CT；秸秆覆盖，SM；垄上覆膜+沟内覆秸秆，RF）和施氮（不施氮，N0；推荐施氮量，N120；习惯施氮量，N240）下土壤质量演变、碳氮功能基因变化，以及团聚体尺度碳氮分布及其酶学特性。.（1）与CT相比，RF和SM显著提高土壤含水量、速效钾、β-葡萄糖苷酶（βG）、磷酸酶和PLFA总量； SM对土壤有机碳（SOC）、纤维二糖苷酶（CBH）、乙酰氨基葡萄糖苷酶（NAG）等生物化学指标提高效果高于RF。与N0相比，N120和N240提高全氮（TN）、NAG、α-葡萄糖苷酶（αG）、微生物量碳（MBC）、微生物量氮（MBN）、革兰氏阴性细菌，但降低土壤pH、有效磷和速效钾。.（2）覆盖模式间土壤质量指数（SQI）表现为SM (0.698) > RF (0.642) > CT (0.620)；不同氮肥管理SQI表现为N240 (0.680) > N120 (0.650) > N0 (0.630)；SM+N240处理SQI最高。塿土土壤质量评价最小数据集：含水量、pH、硝态氮、有效磷、NAG和放线菌。.（3）与CT相比，SM显著提高氨氧化古菌（AOA）和氨氧化细菌（AOB），而RF则降低AOA。覆盖模式下，AOB随施氮量增加而增高，土壤硝化潜势与AOB变化规律一致。习惯施氮量下，cbhI和GH48基因丰度分别表现为SM > RF ≈ CT和SM ≈ RF > CT。.（4）与CT相比，RF和SM显著提高大团聚体比例及团聚体稳定性。与N0相比，施氮提高土壤微团聚体以及大团聚体中微团聚体含量。SOC和TN随团聚体粒径的增大而升高，覆盖增加大团聚体、微团聚体和大团聚体中微团聚体中SOC，其SM增加效果高于RF。土壤团聚体中TN变化规律与有机碳相似。与N0相比，N120和N240显著提高大团聚体中TN；而施氮对团聚体中SOC无显著影响。.（5）覆盖和施氮提高团聚体尺度CBH、αG、NAG、亮氨酸氨基肽酶活性。碳循环相关水解酶和NAG在粉黏粒中最高；酚氧化酶和过氧化物酶活性则在微团聚体中最高；MBC、MBN在大团聚中最高。覆盖和施氮显著提高大团聚体中微生物量，且以SM+N240处理MBC含量最高。.总之，该研究成果将为西北旱区农田秸秆还田提供重要的理论依据和数据支撑。