National Natural Science Foundation of China(41771266,41401243),National Key Research and Development Project(No. 2018YFD0800606). Research Fund of State Key Laboratory of Soil and Sustainable Agriculture,Nanjing Institute of Soil Science,Chinese Academy of Science(No. Y812000005),the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2017391)
Nitrous oxide (N2O), a potent greenhouse gas, is produced and reduced mainly under the mediation of functional microorganisms in soil. In terrestrial ecosystems, soil is an important source of N2O emission. Soil aggregates, a key structural component of the soil, consist of sand, silt, clay (primary particles), organic matter (binding agents) and pore spaces. According to the hierarchy theory, soil aggregates can be divided into four fractions by size, that is, large macroaggregates (>2 mm), small macroaggregates (2-0.25 mm), microaggregates (0.25-0.053 mm) and silt plus clay-sized particles (<0.053 mm). Large macroaggregates are high in pore connectivity and oxygen diffusion rate, fast in turnover, and rich in organic matter, and microaggregates high in water retention capacity and stable carbon content, and capable of protecting microorganisms from being predated. Hence, soil aggregates different in size may offer heterogeneous microhabitats for fungi and bacteria. And each independent microhabitat could be regarded as a biogeochemical reactor producing greenhouse gas. Nitrifiers and denitrifiers, which carry functional genes amoA, narG/napA, nirK/nirS, are identified as the major contributors to N2O production. However, N2O reduction is primarily a single process catalyzed by N2O reductase, encoded by nosZI and nosZII genes, which are present in bacteria and archaea capable of complete denitrification and acting as non-denitrifiers in N2O reduction to N2. These microorganisms are distributed separately in polymerized reactors different in size, driving N2O production and transportation as affected by soil moisture status, substrate availability, and porous connectivity. However, so far little is known about community structure of the nitrifiers and denitrifiers in aggregates relative to particle size and its influences on N2O emission. Nowadays, a numerous of studies have been reportedly devoted to soil N2O emission characteristics in different ecosystems, but limited knowledge was achieved on N2O emission and relative contribution of soil aggregates relative to size fraction. Therefore, with the clarification of functional microbial distribution at the aggregate scale, hot-spots of N2O production and reduction in soil microhabitats could be specified. In this review, advances in the recent research are summarized on divergence of N2O emission from soil aggregates. Large macroaggregates and small macroaggregates were found emitting more N2O than microaggregates did. However, studies were also found reporting conversely that microaggregates emitted N2O more vigerously. Papers in the literature also reported relationships between aggregate turnover(the formation, stabilization and disintegration of soil aggregates)and microbial structure dynamics. Bacteria contribute strongly to the formation of both macro- and microaggregates, while fungi play an important role in the formation of large macroaggregates. Hence, the mechanisms of soil microbes producing and reducing N2O in soil microhabitats could be summed up. A large number of studies have shown that ammonium oxiders are abundant in macroaggregates (>0.25 mm) and a dominant denitrifier community in microaggregates (<0.25 mm), and environmental factors affect N2O emission via redistributing these functional microorganisms. Based on the current results, discussions are done of some perspectives for future investigations: potential hot-spots for soil N2O production at the aggregate scale as heterogenetic living niches existing in soil aggregates different in size, critical values of key environmental parameters impacting soil N2O production and reduction, and holistic research on functional gene groups and enzymes instead of some individual gene due to the complex participation of soil microbes in N2O production and reduction. It is expected that this study will provide a reference for modeling and parameter optimization and a solid theoretical basis for mitigation of N2O emissions.
李文娟,蔡延江,朱同彬,黄平.土壤团聚体氧化亚氮排放及其微生物学机制研究进展[J].土壤学报,2021,58(5):1132-1144. DOI:10.11766/trxb202008240311 LI Wenjuan, CAI Yanjiang, ZHU Tongbin, HUANG Ping. Release of Nitrous Oxide from Soil Aggregates and Its Microbial Mechanism[J]. Acta Pedologica Sinica,2021,58(5):1132-1144.复制