生物质炭对土壤N2O消耗的影响及其微生物影响机理

生物质炭在温室气体减排方面具有很大的发展前景，它不仅能实现固碳，对于在大气中停留时间长且增温潜势大的N₂O也能发挥积极作用。本研究采用室内厌氧培养试验，按照生物质炭与土壤质量比（0、1%和5%）加入一定量生物质炭，土壤重量含水率控制在20%。利用Robotized Incubation平台实时检测N₂O和N₂浓度变化，通过测定土壤中反硝化功能基因丰度（nirK、nirS、nosZ）分析生物质炭对N₂O消耗的影响及其微生物方面的影响机理。结果表明：经过20 h厌氧培养后，0生物质炭处理的反硝化功能基因丰度（基因拷贝数·g^-1）分别为6.80×10⁷（nirK）、5.59×10⁸（nirS）和1.22×10⁸（nosZ）。与0生物质炭处理相比，1%生物质炭处理的nirS基因丰度由最初的2.65×10⁸基因拷贝数·g^-1升至7.43×10⁸基因拷贝数·g^-1，nosZ基因丰度则提高了一个数量级，由4.82×10⁷基因拷贝数·g^-1升至1.50×10⁸基因拷贝数·g^-1，然而nirK基因丰度并无明显变化；5%生物质炭处理的反硝化功能基因丰度并未发生显著变化。试验结束时，添加生物质炭处理的N₂/（N₂O+N₂）比值也明显高于0生物质炭处理。相关性分析结果表明，nirS基因丰度和nosZ基因丰度均与N₂O浓度在0.01水平上显著相关。试验末期nirS基因丰度和nosZ基因丰度均随着N₂O浓度的降低而升高。因此在本试验中，添加1%生物质炭可显著提高nirS和nosZ基因型反硝化细菌的丰度，增大N₂/（N₂O+N₂）比值，促进N₂O彻底还原成N₂。生物质炭对于N₂O主要影响机理是增大了可以还原氧化亚氮的细菌活性，促进完全反硝化。

Biochar's effect on soil N2O consumption and the microbial mechanism

Biochar is a promising material for mitigating greenhouse gas emissions. In addition to carbon sequestration, it has positive effect on the ozone-depleting gas nitrous oxide (N₂O), which is with long residence time and strong warming potential. In this research effort, an anaerobic incubation experiment was conducted. Three treatments with different biochar application rates were set, taking account of biochar to soil ratio (w/w):0 (0BC), 1% (1%BC) and 5% (5%BC). Soil gravimetric water content was controlled at 20%. According to the robotized incubation platform providing real-time determination of N₂O and N₂ concentrations and soil denitrification functional gene abundance measurement, we analyzed the impact of biochar on N₂O consumption and biological mechanisms. The main results indicated that after a 20-hour anaerobic incubation, the denitrification functional gene abundance of 0BC treatment was 6.80×10⁷ (nirK), 5.59×10⁸ (nirS), 1.22×10⁸ (nosZ) gene copies per gram soil, respectively. Compared with 0BC treatment, the nirS gene abundance of 1%BC treatment increased from the initial 2.65×10⁸ to 7.43×10⁸ gene copies per gram soil, while, the nosZ gene abundance increased by an order of magnitude from 4.82×10⁷to 1.50×10⁸ gene copies per gram soil. However, there was no significant change in nirK gene abundance. And the denitrification functional gene abundance of 5%BC treatment did not show marked variations. In conclusion, the N₂/(N₂O+N₂) ratio of treatments with biochar application was clearly higher than 0BC treatment. The results of correlation analysis showed that nirS and nosZ gene abundance was significantly correlated with the N₂O concentration at 0.01 level, and the abundance of nirS and nosZ genes all increased as N₂O concentration declined at the end of the experiment. Therefore, in the present trial, a 1% biochar addition significantly increased the abundance of denitrifying bacteria with nirS and nosZ genotypes and N₂/(N₂O+N₂) ratio, and promoted the complete reduction of N₂O to N₂. The main mechanism of the biochar effect on N₂O emission was the enhanced reduction activities and gene expression of nosZ-containing microorganisms, resulting in complete denitrification.