摘要:翻耕会使耕层土壤发生显著位置交换。耕层土壤位置交换会通过影响土壤物理、化学和生物性状，改变氮素转化过程。本文研究了土层交换对黄淮海平原南端砂姜黑土硝化、反硝化过程和玉米生长及氮素利用的影响，为该区域选择合理的耕作方式、减少氮素损失及提高氮素利用效率提供理论依据。试验在人工气候室条件下，以土壤（0~35 cm）田间原位分层作为常规土层处理（CK），以原位0~10 cm和10~20 cm土层交换后作为土层交换处理（SE），并用20 μm的尼龙网区分非根际和根际土壤。于玉米小喇叭口期利用荧光定量PCR技术测定土壤氨氧化微生物和反硝化菌群丰度，并结合非根际和根际土壤的硝化潜势、土壤呼吸、反硝化能力、反硝化潜势、土壤理化性质和玉米总氮含量及根系形态的测定，探讨土层交换对土壤氮素转化和玉米生长及氮素利用的影响。结果显示，SE处理的玉米植株氮吸收量比CK处理显著降低8.9%（P < 0.05）。土层交换显著影响根际而不是非根际土壤的硝化潜势，使其显著降低13.5%（P < 0.05）；并使非根际和根际土壤的反硝化能力分别提高36.6%（P < 0.05）和8.4%（P < 0.05）。土层交换使非根际和根际土壤的可溶性有机碳含量分别提高11.7%（P < 0.05）和5.2%。相关分析显示硝化潜势与氨氧化细菌（AOB）丰度呈显著正相关（r=0.91**），与氨氧化古菌（AOA）丰度无显著相关关系；反硝化能力与土壤可溶性有机碳和呼吸速率呈显著正相关（r=0.89**和0.93**），与nirK、nirS拷贝数无显著相关性；玉米植株氮吸收量与根际土壤的硝化潜势、根表面积×AOB拷贝数都呈显著正相关（r=0.83*和0.86*），而与反硝化能力呈显著负相关（r=-0.88**）。以上结果表明砂姜黑土土壤硝化速率的降低和反硝化速率的增强，是土层交换后玉米氮素利用效率低的重要原因。AOB是硝化速率的主要驱动微生物。土层交换后土壤可溶性有机碳是反硝化能力的关键主导因子。在翻耕条件下，有效调节土壤可溶性有机碳含量是提高作物氮肥利用效率的关键。
关键词:土层交换/
玉米/
根际/
硝化/
反硝化/
氮素利用
Abstract:Soil layers are exchanged during tillage practices, which may change the nitrogen (N) transformation process by affecting the physicochemical and biochemical properties of the soil. In this study, the effects of soil layers exchange on the nitrification and denitrification of lime concretion black soil, maize growth, and N utilization were studied to provide a theoretical basis for selecting reasonable tillage methods, reducing N loss, and improving N use efficiency in the southern region of the Huang-Huai-Hai Plain. In an artificial climate chamber, a normal soil layer distribution (0-35 cm of soil placed in a root box according to in situ soil layers) was used as the control treatment (CK). In-situ 0-10 cm and 10-20 cm soil layers were exchanged and placed in another group of root boxes, which were used as the soil layers exchange (SE) treatment group. A 20 μm nylon mesh was used to separate the rhizosphere and the bulk soil. To investigate the effects of soil layer exchange on soil N transformation, nitrification potential, respiration, denitrifying capacity, denitrification potential, physicochemical properties of the rhizosphere and bulk soil, as well as maize growth, and N use, total N content, and root morphology were investigated at the maize small trumpet stage. The results showed that maize N uptake in SE treatment was 8.9% lower than that of CK (P < 0.05). Soil layer exchange significantly affected the rhizosphere rather than the bulk soil, which reduced its nitrification potential by 13.5% (P < 0.05) and increased the denitrification capacity of the rhizosphere and the bulk soil by 36.6% (P < 0.05) and 8.4% (P < 0.05), respectively. Soil layers exchange increased the soluble organic carbon content of the rhizosphere and bulk soil by 11.7% (P < 0.05) and 5.2%, respectively. Correlation analysis showed that nitrification potential was significantly positively correlated with the abundance of ammonia-oxidizing bacteria (AOB, r=0.91**), but was not significantly correlated with the abundance of ammonia-oxidizing archaea (AOA). Denitrification capacity was significantly positively correlated with soluble organic carbon and soil respiration (r=0.89** and 0.93**), but showed no correlation with nirK or nirS gene copy number. N uptake by maize plants was positively correlated with the nitrification potential of the rhizosphere and the total root surface area×AOB gene copy number (r=0.83* and 0.86*), but was significantly negatively correlated with denitrification capacity (r=-0.88**). These results indicated that a decrease in the nitrification rate and an increase in the denitrification rate in lime concretion black soil could result in low N use efficiency by maize after soil layers exchange. The nitrification rate was driven more by AOB abundance. After soil layers exchange, soil soluble organic carbon was the key driving factor for denitrification capacity. Effective regulation of soil soluble organic carbon content is the key to improving crop nitrogen use efficiency under tillage conditions.
Key words:Soil layer exchange/
Maize/
Rhizosphere/
Nitrification/
Denitrification/
Nitrogen utilization
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