长期施肥下稻麦轮作体系土壤团聚体碳氮转化特征

Soil aggregate is key component of soil structure, and is an important mechanism contributing to soil fertility as it mediates the turnover rate of soil organic matter and nutrition cycling. Understanding the transformation characteristics of carbon (C) and nitrogen (N) in soil aggregates is thus very important for balanced fertilization. Based on a long-term fertilizer experiment over 33 years in a paddy soil derived from yellow-brown earth, we characterize the distribution of C and N and the chemical structure of humus in soil aggregates, and analyze the soil biological characteristics, including microbial biomass C and N and enzyme activities involved in the cycling of C and N. We also reveal comprehensively the microbial community structure in different particle-size aggregates by illumina MiSeq platform. The abundance and diversity of the functional genes involved in cellulose degradation, nitrification and denitrification are also investigated. This research will contribute to explore the underlying mechanism of interaction between soil structure, microorganism and nutrient cycling, and the outcome through this research would be of great practical significance to balanced fertilization, improvement of the quality of cultivated land, so as to realize sustainable utilization of farmland.

团聚体是土壤的最基本结构单元，是土壤肥力的物质基础，是有机质分解与积累、养分迁移与转化的主要场所，理解不同施肥制度下土壤团聚体碳氮转化特征是科学施肥的关键所在。因此，本项目拟以代表华中地区典型土壤的黄棕壤性水稻土长达33年的肥料长期定位试验为基础，研究长期施用有机肥料和无机肥料条件下土壤团聚体有机碳、氮的分布特点及腐殖质结构特征，团聚体微生物量碳、氮的消长规律，土壤胞外酶在团聚体碳、氮转化中的作用特点，以及不同粒径团聚体中微生物的群落结构特征和参与碳、氮转化的功能微生物数量和多样性。研究结果对于理论上深入揭示土壤结构-微生物-土壤养分三者之间的相互作用机制，实践上指导平衡施肥，提高耕地质量，实现农田可持续利用具有重要意义。

本研究以稻麦轮作体系有机培肥长期定位试验为基础，利用交叉极化-魔角旋转固态13C核磁共振技术（CP/MAS 13C-NMR）、磷脂脂肪酸分析（PLFA）、定量PCR（qPCR）、末端限制性片段长度多态性（T-RFLP）、454高通量测序等现代分子生态学技术，研究不同粒径团聚体碳氮分布、腐殖质结构特征、与碳氮转化相关的胞外酶活性、微生物群落结构分异特征、参与土壤氨氧化及纤维素分解过程的功能微生物多样性。研究取得了如下主要进展：（1）长期施肥影响了黄棕壤性水稻土土壤团聚体组成，麦季土壤以粉粒和大团聚体为主，稻季以粗砂和粉粒为主，细砂含量在两季均最低。有机无机肥料配施显著降低了大团聚体的比例，提高了粗砂粒径的比例，改善了土壤结构。细砂粒径的有机碳、全氮含量及碳氮比显著高于其他粒径，施用有机肥显著提高了团聚体土壤有机碳、全氮含量，降低了土壤碳氮比。（2）土壤胞外酶活性与土壤有机碳、全氮、碳氮比显著相关。十种胞外酶除磷酸酯酶和硫酸酯酶外，其余胞外酶均在细砂土壤中活性最高。有机无机配施显著提高了土壤团聚体胞外酶活性。（3）磷脂脂肪酸总量均呈大粒径团聚体（>63 μm）大于粉粘粒（63-0.1 μm）的规律，以粉粒中最低。施用有机肥提高了耕层及各土壤团聚体的磷脂脂肪酸总量。（4）稻季土壤的氨氧化微生物数量高于麦季，有机无机配施处理显著提高了氨氧化细菌丰度。尽管氨氧化古菌数量是氨氧化细菌数倍，氨氧化细菌群落结构对施肥及团聚体粒径的响应更为敏感。（5）参与纤维素转化的真菌糖苷水解酶cbhI基因和细菌糖苷水解酶GH48基因丰度均在细砂中最高，粘粒中最低，且在有机肥的施用下普遍增加。纤维素分解基因在腐殖化程度较低的粒径中（>63 μm）较为丰富，而在腐殖化程度较高的粒径（63-0.1 μm）中丰度较低。. 施肥影响了土壤团聚体组成，施肥措施与团聚体粒径与胞外酶活性、微生物群落结构、氨氧化微生物和水解酶基因丰度有显著相关关系。研究表明,有机无机配施改良了土壤结构，促进了土壤团聚体碳氮转化，有利于土壤肥力提升。