生物炭对桉树人工林酸性土壤N2O排放的影响及微生物响应机制

The soil acidification of Eucalyptus plantation in the southern Chinese province was obvious recently,which aggravated soil nitrous oxide (N2O) emissions in acidic Eucalyptus plantation to some extent. Soil nitrification and denitrification is usually occurring simultaneously.The mechanism of microbe and its contribution to N2O emissions need to be studied further because that ammonia oxidizing bacteria(AOB),ammonia oxidizing archaea(AOA) and fungi may all play an important role in nitrification of acid soil. Wastes from forestry is an ideal material for biochar,which are helpful to reduce soil N2O emissions etc. It is important for us to explore the source of soil N2O emission and microbial transformation in Eucalyptus plantation under the regulatory role of biochar addition especially now. On the basis of our previous research ,we already had some biochar that were made from forestry waste of Eucalyptus plantation. Therefore, a biochar addition control experiment will be designed in Eucalyptus plantation acid soil in Guangxi province, which were the largest district of Eucalyptus plantations in China. Effects of biochar on soil N2O emission will be measured by the static chamber-gas chromatography method. The contributions of nitrification and denitrification to soil N2O emission will be calculated by the barometric process separation (BaPS) method and stable isotope techniques (δ15N，δ18O) . At the same time, the key processes and microbial mechanisms of biochar on soil N2O emission were also studied through modern molecular biology methods, such as real time fluorescence quantitative PCR, DNA sequencing and phylogenetic analysis ,and so on.The relative contribution of fungi to soil N2O emission was determinated by substrate induced respiration and 15N natural abundance method respectively. These results will provide some information for applying biochar to reduce soil N2O emission in forest production. The scientific data for the forest sustainable management policy would be suggested for Eucalyptus Plantation.

目前我国桉树人工林土壤出现酸化现象，加剧了酸性土壤N2O的排放。土壤硝化作用与反硝化作用通常耦合发生，氨氧化细菌，氨氧化古菌和真菌都有可能在酸性土壤硝化作用中起重要作用，其反应机制及其对N2O排放的贡献还需进一步明确。生物炭在减缓土壤N2O排放等方面有重要的作用，生物炭调控下，识别桉树人工林酸性土壤N2O排放的来源途径及微生物响应机制，对于桉树人工林N2O减排具有重要意义。该研究以广西桉树人工林酸性土壤为研究对象，开展生物炭(前期桉树废弃物制备)施用试验，通过静态箱—气相色谱法，结合气压过程分离法(BaPS)和稳定性同位素技术(δ15N，δ18O)，探讨土壤N2O的排放特征及来源途径；借助实时荧光定量PCR等现代分子生物学手段，揭示生物炭对土壤氨氧化微生物群落结构的影响，通过底物诱导呼吸抑制法和15N自然丰度，阐明真菌在土壤N2O排放的相对贡献，旨在为桉树人工林可持续经营提供科学依据。

我国桉树人工林土壤出现酸化现象，加剧了酸性土壤N2O的排放。土壤硝化作用与反硝化作用通常耦合发生，氨氧化细菌，氨氧化古菌和真菌都有可能在酸性土壤硝化作用中起重要作用。生物炭在减缓土壤N2O排放等方面有重要的作用，生物炭调控下，识别桉树人工林酸性土壤N2O排放的来源途径及微生物响应机制，对于桉树人工林N2O减排具有重要意义。该研究以广西桉树人工林酸性土壤为研究对象，开展生物炭施用试验，明确了土壤N2O的排放特征及来源途径，揭示了生物炭对土壤氨氧化微生物群落结构的影响，探讨了真菌在土壤N2O排放的相对贡献。结果表明，施用生物炭是提高土壤碳储量和活性有机碳含量的有效措施。生物炭处理下土壤平均净硝化速率相比对照降低了37.15% ~89.08%，生物炭添加抑制了土壤的硝化作用，对氮素硝化作用的抑制作用随施用量的增加而增强。硝化过程是 N2O的主要来源且主导了N2O排放，反硝化作用产生的N2O较少。来自自养硝化作用产生的N2O约占78.6 %~86.7 %，异养硝化作用约占0.84 %~0.96 %，反硝化作用约占 12.46 %~20.44 %，施用生物炭对自养硝化、异养硝化、反硝化作用产生N2O的相对贡献有影响显著。生物炭通过增加AOB、AOA、amoA、nirS 和 nirK基因丰度间接降低N2O排放，同时通过增加nosZ基因丰度促进N2O还原，整体表现为降低了桉树人工林土壤N2O的排放，4%生物炭量施用下对硝化作用抑制和N2O的减排综合效果最好。生物炭增大了可以还原氧化亚氮的细菌的活性，促进完全反硝化。土壤N2O排放与pH值之间呈极显著负相关关系，土壤pH值的升高可能也是引起N2O排放量降低的重要原因。施用生物炭能改善桉树人工林酸化土壤性质，增加功能基因丰度，降低土壤N2O排放，是一种固碳和N2O减排的较好措施。