Zhen,Y.,Sara, K.,Tianran,S.,Ruben, K. and Andreas,K. Effect of Redox Activity and Conductivity of Biochar Particles on Methane Emission and Fe(III) Reduction in Anoxic Paddy Soil Zhen,Y.,Sara, K.,Tianran,S.,Ruben, K. and Andreas,K.

Electron Transfer by Biochar Redox activity electrons accepted and donated by functional groups of biochar Conductivity a rapid electron transfer by carbon matrice in biochar Arrow thickness indicates e- transfer kinetics Pathway 2. 600-700 °C Pathway 3. 700-800 °C Geoconductor mechanism Geobattery mechanism External electron acceptors Pathway 1. 400-600 °C External electron donors e- e- flow (Klüpfel, L. et al., 2014) 2 (Sun, T.R. et al., 2017)

Biochar as Electron Shuttle Biochar functions as an electron shuttle (e- transfer via functional groups of biochar) transferring electrons between microbes and Fe(III) minerals Biochar addition influences the rate and extent of microbial Fe(III) reduction ferrihydrite hematite Fe(III) mineral Shewanella oneidensis MR-1 e- O OH (Kappler. A et al., 2014 ; Xu. S. et al., 2017) 3

Competition for Electron Donor between Microbial Fe(III) Reduction and Methanogenesis Oxic Anoxic acetate Fe(III) reduction methanogenesis FeIII FeII e- CO2 CH4 Fe(III)-reducing bacteria methanogenic archaea CO2 4

Competition for Electron Donor between Microbial Fe(III) Reduction and Methanogenesis Oxic Anoxic acetate Fe(III) reduction methanogenesis FeIII FeII e- CO2 CH4 Fe(III)-reducing bacteria methanogenic archaea CO2 5

Biochar addition stimulate microbial Fe(III) reduction (in paddy soil) Competition for Electron Donor between Microbial Fe(III) Reduction and Methanogenesis Biochar addition stimulate microbial Fe(III) reduction (in paddy soil) Oxic Anoxic acetate Fe(III) reduction methanogenesis Biochar Redox functional groups and conductive carbon matrices in biochar FeIII FeII e- CO2 CH4 Fe(III)-reducing bacteria methanogenic archaea CO2 6

Competition for Electron Donor between Microbial Fe(III) Reduction and Methanogenesis Biochar:Fe(III) mineral ratios control microbial Fe(III) reduction by functioning as electron shuttle, conductor and capacitor (in Shewanella MR-1 suspension) Oxic Anoxic acetate Fe(III) reduction methanogenesis Biochar Redox functional groups and conductive carbon matrices in biochar FeIII FeII e- CO2 CH4 Fe(III)-reducing bacteria methanogenic archaea CO2 (Submited) 6

Competition for Electron Donor between Microbial Fe(III) Reduction and Methanogenesis Biochar addition was shown to inhibit or stimulate methanogenesis with partially controdictory results in the literatures Oxic Anoxic acetate Fe(III) reduction methanogenesis Biochar Redox functional groups and conductive carbon matrices in biochar FeIII FeII e- CO2 CH4 Fe(III)-reducing bacteria methanogenic archaea CO2 7

Research Questions Do biochar particle size and biochar:Fe(III) mineral ratios influence the competition between microbial Fe(III) reduction and methanogenesis? Is this associated with changes in the microbial community composition? 8

Results and Conclusions Biochar particle sizes and biochar:Fe(III) mineral ratios influence microbial communities and electron transfer pathways This controls the competiton between microbial Fe(III) reduction and methanogenesis in anoxic paddy soil Welcome to poster board 429 in Session 12f, Wednesday @ 17:30 - 19:30 ! 9

Acknowledgements Geomicrobiology group (Tübingen) Center for Applied Geosciences Geomicrobiology Acknowledgements Geomicrobiology group (Tübingen) Microbial Ecology group (Tübingen) D. Straub (University of Tübingen, Geoscience) J. G. Usack (University of Tübingen, Environmental Biotechnology) 10