Response of Nitrite-dependent Anaerobic Methane Oxidation in Paddy Fields to Slow Increase of Atmospheric CO2 Concentration

School of Applied Meteorology,Nanjing University of Information Science and Technology,Nanjing 210044,China

Slow increase of CO2 concentration%N-damo%Activity%Community structure%Paddy soil

[Objective]The process of nitrite-dependent anaerobic methane oxidation(n-damo)catalyzed by Candidatus Methylomirabilis oxyfera(M.oxyfera)-like bacteria links both the carbon and nitrogen cycles,and has attracted great attention in recent years because of its potential role acting as a microbial methane sink.This process has been reported to be a novel pathway for controlling methane emissions from paddy ecosystems.Elevated atmospheric CO₂ concentration can indirectly affect the structure and function of soil microbial communities.However,the response of n-damo to e[CO₂]is poorly known.This study aims to explore the response of n-damo activity,and the community composition and abundance of M.oxyfera-like bacteria to e[CO₂]in a paddy ecosystem.[Method]Here,ambient CO₂ treatment(CK)and a slow increase of atmospheric CO₂ treatment(EC:an increase of 40μL·L^–1 per year above CK until 160μL·L^–1)were set up based on the CO₂ automatic control platform with open-top chambers.The stable isotope tracer experiment,quantitative PCR and high-throughput sequencing were employed to investigate the n-damo activity,abundance,diversity and community composition of M.oxyfera-like bacteria in paddy soils across three key rice growth stages(tillering,jointing and flowering stages)under different CO₂ treatments.[Result]The results showed the occurrence of n-damo activity and the presence of M.oxyfera-like bacteria in the studied paddy soils.It was found that the n-damo activity ranged from 0.31 to 5.09 nmol CO₂·g^–1·d^–1,and the abundance of M.oxyfera-like bacteria varied between 7.51*10⁶ and 5.49*10⁷ copies·g^–1.Furthermore,EC treatment stimulated the n-damo activity and abundance of M.oxyfera-like bacteria,particularly at the jointing stage,in which the activity and abundance were increased by 137.9%and 96.0%,respectively.In addition,EC treatment significantly changed the community composition and diversity of M.oxyfera-like bacteria,and the diversity was increased under EC treatment.Correlation analyses showed that the soil dissolved organic carbon content,ammonium content,nitrate content and water content all had significant impacts on the community structure of M.oxyfera-like bacteria.The variations in soil dissolved organic carbon content and inorganic nitrogen content under EC treatment could probably cause the change of n-damo activity and the abundance of M.oxyfera-like bacteria.[Conclusion]Elevated atmospheric CO₂ promoted the n-damo activity and M.oxyfera-like bacterial abundance and significantly changed the community structure of M.oxyfera-like bacteria in a paddy ecosystem.In addition,the changes of soil dissolved organic carbon content,inorganic nitrogen content and water content greatly affected the n-damo activity and community structure of M.oxyfera-like bacteria.Taken together,our results showed a positive response of n-damo to the slow increase of atmospheric CO₂ concentration.