Aerobic release and biodegradation of dissolved organic matter from frozen peat: Effects of temperature and heterotrophic bacteria

• Published in: Chemical Geology
• Main Authors: Payandi-Rolland, Daheydrey, S.Shirokova, Liudmila, Nakhle, Paty, Tesfa, Marawit, Abdou, Ahmed, Causserand, Carole, Lartiges, Bruno, Rols, Jean-Luc, Guerin, Frédéric, Benezeth, Pascale, S.Pokrovsky, Oleg
• Other Authors: Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDE]Environmental Sciences; [SDU]Sciences of the Universe [physics]; Arctic; Climate change; permafrost; Thermokarst
• Online Access: https://hal.science/hal-03004332; https://hal.science/hal-03004332/document; https://hal.science/hal-03004332/file/uncorrected%20proof%20-%20Aerobic%20release.pdf; https://doi.org/10.1016/j.chemgeo.2019.119448

International audience Understanding the conditions of dissolved organic matter (DOM) release from thawing peat in the Arctic regions and identifying the pathways of processing DOM by soil and aquatic heterotrophic bacteria are critical in the context of rapid climate change. Until now, experimental approaches did not allow quantitative predictions of temperature and biota effects on carbon release from peat in permafrost-affected aquatic environments. In this study, we incubated frozen peat and its aqueous leachate at various temperatures (4, 25 or 45°C), with and without culturable heterotrophic bacteria Iodobacter sp., extracted from thermokarst lakes, to quantify the release and the removal rate of organic carbon (OC) with time. The metabolic diversity of the native microbial community associated with the substrates involved in OC processing was also characterized. Transmission electron microscopy revealed that, after degradation, the associated bacteria are mostly located in the inner parts of plant cells, and that the degradation of organic matter around bacteria is more pronounced at 4 and 25°C compared to 45°C. The metabolic diversity of heterotrophic bacteria was equally high at 4 and 25°C, but lower at 45°C. Regardless of the microbial consortium (native community alone or with added culturable heterotrophs), both the OC release from peat and the OC removal from peat leachate by bacteria were similar at 4 and 25°C. Very low apparent activation energies of DOM biodegradation between 4 and 25°C (−4.23 ± 12.3 kJ mol − 1) suggest that the short-period of surface water warming in summer would have an insignificant effect on DOM microbial processing. Such duration (1-3 weeks) is comparable with the water residence time in peat depressions and permafrost subsidences, where peat degradation and DOM microbial processing occur. This questions the current paradigm of a drastic effect of temperature rise on organic carbon release from frozen peatlands, and should be considered for modelling short-term climate ...