At present, the interference of human activities on the nitrogen cycle is far greater than other elements, greatly accelerating the changes in the earth's ecological environment, triggering serious adverse effects such as severe imbalances in the nitrogen cycle, intensification of nitrogen pollution, and an increase in greenhouse gas emissions. It is estimated that only about 40-60% of the world's nitrogen is generated by denitrification and returned to the atmosphere. Under the dual pressure of global warming and increased pollution, whether there is a new type of nitrogen cycle is worth exploring. The discovery of anammox reactions is a clear example. Anaerobic ammonia oxidation directly oxidizes ammonia nitrogen to nitrogen with nitrite as electron acceptor under anaerobic conditions, avoids the production of powerful greenhouse gas N2O, and completes closed nitrogen production cycle .
Zhu Guibing Research Group, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, proposed that the interface of two-phase materials, especially anoxic-aerobic, was discovered after the discovery of the presence of an anaerobic ammonia oxidation reaction zone in the land-rain transition zone of the Baiyang Lake depression-gully system. At the interface, a wide range of anammox reactions are likely to occur.
First of all, I wish the Guibing Research Group and the researcher Zhu Yongguan to cooperate on the scale of micrometers and centimeters to demonstrate that there is an extensive anaerobic ammonia oxidation reaction at the anoxic-aerobic interface. The typical rice rhizosphere and non-rhizosphere soils were collected and CARD-FISH, qPCR, and isotope tracing methods were used to prove that significant anaerobic ammonia oxidation occurred in the rice rhizosphere soil. The amount of nitrogen produced accounted for 30-40 of the total production. %, but the amount of nitrogen produced in the non-rhizosphere soil is only 2-3% of the total nitrogen production, demonstrating significant anaerobic ammonia oxidation reactions in rice rhizosphere soils at micrometer and cm scale. The paper was published in The ISME Journal.
After the above-mentioned small-scale verification, Zhu Guibing’s research group expanded its research site, conducted large-scale verification nationwide, and also estimated the contribution of anaerobic ammonia oxidation reactions to the nitrogen cycle of China’s aquatic ecosystem.
A large-scale sampling study of 10 256 samples from 40 different regions has confirmed that anaerobic ammonia oxidation is ubiquitous in terrestrial water ecosystems, even in extreme environments such as high temperatures (greater than 75°C). Anaerobic ammonia oxidation reactions occur in different water bodies at low temperatures (below -25°C), high pH values ​​(greater than 9), low pH values ​​(less than 4), eutrophication, and oligotrophic salts. The anaerobic ammonia oxidation reaction occurs mainly in the area above 50 cm in surface sediments and plays an important role in the nitrogen cycle. Compared with river systems, lakes have more significant anaerobic ammonia oxidation reactions. The reaction rate is an order of magnitude multiple of the anammox reaction rate in rivers, where the lake shoreline is the heat of anaerobic ammonia oxidation in the entire aquatic ecosystem. Area. The anaerobic ammonia oxidation reaction occurs extensively in the paddy field system, supplementing the nitrogen cycle theory system of soil ecosystems, providing scientific reference for the accurate calculation of N2O emissions from rice field systems in China. The widespread occurrence of anaerobic ammonia oxidation reactions in swamp wetlands will increase scientists' understanding of the conditions under which anaerobic ammonia oxidation occurs, from traditional high-nitrogen, low-carbon environments to high-carbon, low-nitrogen environments, combined with various wetlands and waters. Based on the area of ​​the ecosystem, the nitrogen loss (2.0TgNyr-1) generated by anaerobic ammonia oxidation was calculated to be 11.4% of the total amount. The paper was published in Scientific Reports and Environmental Microbiology Reports.
At the same time, Zhu Guibing’s research group also conducted functional microbes that symbiotic with anaerobic ammonia bacteria, such as ammonia oxidizing archaea (AOA) and nitrite-dependent anaerobic methane oxidization (N-DAMO). Related research papers published in Scientific Reports and Environmental Microbiology Reports.
The above results have an important impact on the flux calculation of N2O, the global climate change model, and the nitrogen cycle flux in China. In the past, the calculation of nitrous oxide fluxes was based on the model and the amount of chemical fertilizers applied, as well as the actual measured values ​​of some of the sites. No consideration was given to the efficacy of anaerobic ammonia oxidation. Therefore, the N2O flux at the national scale is likely to be less than the current estimate.
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