1) 针对水田系统,利用MIMS和15N示踪手段(15N同位素配对和15NH4+化学氧化法),率先在同一体系下同时研究了水稻土中反硝化、Anammox和DNRA的发生速率和影响因素,并对室内泥浆15N加标法和土柱培养法进行了对比分析。发现反硝化是硝酸根还原的主导途径(76.9%-92.5%),Anammox和DNRA也有实质性贡献(占比分别为4.5-9.2 %和0.5-17.6%);室内泥浆15N加标法能一定程度反应土壤原位净脱氮速率,但会显著低估(Shan et al ., Environ. Sci. Technol. 2016)。进一步通过室内培养实验,明确了关键环境因子如温度、pH、有机碳、底物浓度等对土壤硝酸根还原过程动力学特征的影响,发现碳源的形态和供给及Fe2+含量是影响这些厌氧氮转化过程的关键因素(Shan et al., Biol. Fertil. Soils 2018; Rahman/Shan et al., Environ. Pollut. 2018; 李进芳等,农业环境科学学报 2019;吴敏等,土壤学报 2021),同时发现土壤和污泥中硝酸根的转化过程也对酚类有机污染物的降解转化具有潜在影响,硝基取代后的酚类有机污染物环境归趋与母体化合物具有明显差异(Wang et al., J. Hazard. Mater. 2020)。
2) 针对旱地系统,通过将RoFlow与15N-N2O site preference (SP)技术联用,揭示了集约化种植体系下果园和蔬菜地等旱地系统中碳源和硝酸根含量对反硝化速率和产物比的调节机制。发现秸秆添加可显著促进土壤N2O排放和反硝化速率,但秸秆添加对反硝化的促进作用及其对反硝化产物比[N2O/(N2O+N2)]的影响取决于土壤硝酸根的含量;通过15N-N2O SP分析显示,田间实际含水量(55-80% WFPS)情况下,细菌反硝化和硝化细菌反硝化过程是旱地系统N2O产生的主导途径;在相同土壤氮含量下,秸秆添加能够显著促进N2O的还原(N2O还原为N2)并提高N2排放峰值,与观测到的N2O还原酶(N2OR)功能基因nosZ的丰度变化趋势相一致,暗示秸秆添加可能对N2O还原功能微生物具有显著影响(Wu et al., 2018; Wei et al., 2020)。而目前已知nosZ包括两个不同的分支:较为熟知的Clade Ⅰ型分支,通常为反硝化微生物携带;以及新的Clade Ⅱ型分支,为多种类型微生物携带,其中大多数是非反硝化微生物。通过对2013-2019年间有关NosZ论文的荟萃分析发现,Clade Ⅱ型N2O还原微生物在影响N2O排放方面具有之前未认识到的重要作用,如其可以消耗非反硝化过程产生的N2O、以N2O为“电子汇”清除多余电子及解除N2O细胞毒害,同时Clade Ⅱ 型N2O还原微生物还具有不同于Clade Ⅰ 型N2O还原微生物的酶促动力学特征,且在许多生态系统的土壤中,Clade Ⅱ型N2O还原微生物的数量占据优势地位。基于上述认识,提出了N2O还原过程中Clade I 和Clade II类型微生物作用的范式图(图1),未来研究须重点关注Clade Ⅱ型N2O还原微生物在调节土壤N2O排放中作用(Shan et al., Glob. Change Biol. 2021)。
论著清单
Shan, J., Zhao, X., Sheng, R., Xia, Y.Q., Ti, C.P., Quan, X.F., Wang, S.W., Wei, W.X., Yan, X.Y., 2016. Dissimilatory nitrate reduction processes in typical Chinese paddy soils: rates, relative contributions and influencing factors. Environmental Science & Technology 50, 9972-9980.
Shan, J., Yang, P., Shang, X., Rahman, M.M., Yan, X., 2018. Anaerobic ammonium oxidation and denitrification in a paddy soil as affected by temperature, pH, organic carbon, and substrates. Biology and Fertility of Soils 54, 341-348.
Rahman, M.M., Shan, J., Yang, P., Shang, X., Xia, Y., Yan, X., 2018. Effects of long-term pig manure application on antibiotics, abundance of antibiotic resistance genes (ARGs), anammox and denitrification rates in paddy soils. Environmental Pollution 240, 368-377.
Wu, D., Wei, Z., Well, R., Shan, J., Yan, X., Bol, R., Senbayram, M., 2018. Straw amendment with nitrate-N decreased N2O/(N2O+N2) ratio but increased soil N2O emission: A case study of direct soil-born N2 measurements. Soil Biology and Biochemistry 127, 301-304.
李进芳, 柴延超, 陈顺涛, 单军, 颜晓元, 2019. 利用膜进样质谱仪测定水稻土几种厌氧氮转化速率. 农业环境科学学报 38, 1541-1549.
吴敏, 李进芳, 魏志军, 李承霖, 夏永秋, 单军, 颜晓元, 2021. 水稻土Fe2+氧化耦合DNRA及其对氧气存在和碳源添加的响应. 土壤学报(接受待刊,已网络预发表).
颜晓元等,2020. 土壤氮循环实验研究方法. 北京:科学出版社 ISBN: 978-7-03-064843-3
Wang, Y., Shan, J., Zhao, Y., Li, F., Corvini, P.F.X., Ji, R., 2020. Degradation and transformation of nitrated nonylphenol isomers in activated sludge under nitrifying and heterotrophic conditions. Journal of Hazardous Materials 393, 122438.
Wei, Z., Shan, J., Chai, Y., Well, R., Yan, X., Senbayram, M., 2020. Regulation of the product stoichiometry of denitrification in intensively managed soils. Food and Energy Security 9, e251.
Shan, J., Sanford, R.A., Chee-Sanford, J., Ooi, S.K., Loeffler, F.E., Konstantinidis, K.T., Yang, W.H., 2021. Beyond denitrification: the role of microbial diversity in controlling nitrous oxide reduction and soil nitrous oxide emissions. Global Change Biology doi: 10.1111/GCB.15545 (In press).