The impact of the nitrification inhibitor calcium cyanamide and an icrease of soil pH on N2O emission and soil bacterial community composition. soil metagenome

Calcium cyanamide is the main component of lime nitrogen. Calcium cyanamide is gradually hydrolyzed into urea and the nitification inhibitor dicyandiamide in soil. In addition, Calcium cyanamide increase soil pH. The aim of this study was to elucidate the impacts of calcium cyanamide and an increase of soil pH on N2O emission and soil bacterial community composition. Soil incubation experiment was conducted with eleven treatments established in combination with five chemical amendments (i.e. urea [U], cyanamide [CN], calcium cyanamide [CaCN], calcium hydroxide [Ca], and urea with calcium hydroxide [CaU]) and two fertilization methods (i.e. whole mixing and local placement in the mid layer), and the control without fertilizer application [CT]. Soil was incubated up to 28 days, and the soil properties and N2O emission were monitored. Soil bacterial community compositions at 7th day were elucidated using the high throughput sequencing. In addition to CN and CaCN, CaU significantly suppressed N2O emission compared to U. The localization of the chemicals had less effect on N2O emission. CaCN, CN and CaU decreased soil bacterial alpha diversity, and Planococcaceae was the dominat family in these environments. Besides, bacterial communities of CaCN, CN and CaU were predicted to have less nitrification and denitrification genes. Compared to CT, bacterial beta diversities were gradually increased along with soil pH increase, whereas Ca showed smaller beta diversity to CT. Our results suggest that an increase of soil pH under high urea concentration could have an important role in shaping the bacterial community composition and suppress N2O emission.

氰胺化钙(Calcium cyanamide)是石灰氮(lime nitrogen)的主要成分。其在土壤中可逐步水解为尿素与硝化抑制剂双氰胺(dicyandiamide)，此外还可提升土壤pH值。本研究旨在阐明氰胺化钙与土壤pH升高对氧化亚氮(N₂O)排放及土壤细菌群落组成的影响。本研究设置11组处理开展土壤培养试验，处理组合包括5种化学改良剂：尿素(U)、氰胺(CN)、氰胺化钙(CaCN)、氢氧化钙(Ca)以及尿素与氢氧化钙复配制剂(CaU)，2种施肥方式：全层混匀施入与中层局部施入，以及不施肥的对照组(CT)。土壤培养周期为28天，期间持续监测土壤理化性质与氧化亚氮排放情况。于培养第7天，采用高通量测序技术解析土壤细菌群落组成。相较于尿素组(U)，除氰胺组(CN)与氰胺化钙组(CaCN)外，尿素-氢氧化钙复配组(CaU)可显著抑制氧化亚氮排放。药剂的施用位置对氧化亚氮排放的影响相对较小。氰胺化钙组(CaCN)、氰胺组(CN)与复配组(CaU)均降低了土壤细菌α多样性，且在上述处理的土壤环境中，动球菌科(Planococcaceae)为优势菌群。此外，研究预测氰胺化钙组(CaCN)、氰胺组(CN)与复配组(CaU)的细菌群落所携带的硝化与反硝化基因丰度更低。与对照组(CT)相比，土壤细菌β多样性随土壤pH升高呈逐渐上升趋势，而氢氧化钙组(Ca)与对照组的β多样性差异较小。本研究结果表明，在高浓度尿素条件下提升土壤pH，对于塑造土壤细菌群落组成及抑制氧化亚氮排放具有重要作用。