硝化加速热区酸性红壤酸化的作用机制及调控

Hot region is the important economic crop planting area in Yunnan province, and is the frontier of ecological barrier of Southwest China. Increasing soil nitrification caused by larger application of N fertilizer has become a major issue in red soil areas in Southern China. The process of autotrophic nitrification of NH4+ releases H+, which leads to soil acidification and causes difficulties in the improvement of the degraded red soil. In our previous study, we found that obvious acidification and enrichment of AOB T-RFs 296 in red soil was related to the high soil nitrification rate. Significant decrease in nitrification rate was also detected in the acid red soils if biochar was applied in the incubation experiment. In this project, we plan to collect the unique red soil from the surface of coffee plantation in hot region of southern Yunnan, which is characterized by both tropical and subtropical monsoon climate. The incubated soil collected from the field experiments and the 15N tracer will be used to study the effect of biochar on the fixation of inorganic nitrogen and the reduction of soil nitrification. The 454 pyrosequencing technology will be used to investigate the contribution of ammonia oxidizing bacteria and archaea to soil nitrification process in acid red soil in hot region. Acid sensitivity indictors will be measured to determine the buffer property of the biochar-mixed soil. Finally, multivariate statistical analysis will be applied to further study the mechanism of soil acidification driven by nitrification process. The results might provide scientific information for N nutrient management and farmland ecosystem sustainable development of degraded red soil in hot region of Yunnan province.

热区是云南重要的经济作物带，西南生态安全屏障的前沿。热区高温气候条件下土壤氮转化快，氮肥硝化作用释放的H+引起的土壤酸化使得退化红壤的治理面临更多困难。土壤酸化与硝化作用强度和土壤缓冲性能密切相关。前期研究表明，硝化速率较高的酸性红壤酸化明显、氨氧化细菌优势种群（T-RFs 296）富集，生物炭显著降低硝化速率。本项目拟以云南热区极具特色的咖啡种植红壤为研究对象，采用15N稀释和富集技术研究田间条件下生物炭无机氮“固定”效应、硝化作用强度及其与土壤酸化的关系；采用高通量测序技术研究施用生物炭后氨氧化微生物的群落特征、对氨氧化的贡献，明确热区酸性红壤硝化过程的主要硝化微生物；采用酸敏感性指标分析生物炭对咖啡种植红壤酸缓冲性能的影响，明确最主要的酸缓冲体系。通过上述工作，阐明生物炭降低硝化加速红壤酸化的作用机制，为云南热区红壤氮素养分管理以及农田生态系统可持续发展提供科学指导。

氮肥硝化作用释放的H+引起的土壤酸化使得退化红壤的治理面临更多困难。以咖啡种植红壤为对象，对土壤酸化与硝化作用强度和土壤缓冲性的关系进行研究，结果表明：（1）硝化速率高的土壤易酸化。0-7d土壤净硝化速率为1.83-7.42 mg·kg-1·d-1，土壤pH值是影响土壤净硝化速率的重要因子，两者之间呈极显著正相关关系（p<0.01）。培养结束后，净硝化速率高的土壤pH值显著下降，0-4d土壤初级硝化速率为1.01-3.44 mg·kg-1·d-1，初级硝化速率更高的土样pH下降幅度更大，表明硝化会加剧土壤酸化。（2）土壤氨氧化古菌Group I.1 a-associated （Candidatus Nitrosotalea）相对丰度在所有硝化细菌中最高，其相对丰度与净硝化速率没有关系，但与初级硝化速率呈极显著正相关（P < 0.01），同时与有效磷和速效钾呈显著正相关（P < 0.05）。（3）在360d培养试验中，施氮（尿素）处理土壤pH值下降1.82个pH单位，添加生物炭的土壤pH值下降2.14-2.38个pH单位，同时pH缓冲容量也在下降。土壤pH、交换性Ca2+、交换性K+和总有机碳是土壤pH缓冲容量的主要影响因子。综上，硝化速率高的土壤易酸化，初级硝化速率高的土壤中氨氧化古菌的相对丰富高。施氮会加速咖啡种植土壤酸化，生物炭缓解土壤酸化的效果不显著，其在热区酸性红壤中的应用还需进一步研究