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

Abstract

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 impacts in these regions.

Spatial and Seasonal Variations of C, Nutrient, and Metal Concentration in Thermokarst Lakes of Western Siberia Across a Permafrost Gradient

“…The pool of total dissolved P (P tot ) was sizably higher in summer relative to spring (a factor of 2-10 for various permafrost zones), but the R summer/spring strongly decreased northward (Figure 11). Thus, the summertime inflow of P from watershed to lakes decreased northward, suggesting that the main source of P is thawed rather than frozen peat and mineral horizons, as also confirmed by experimental modeling of peat core interaction with aqueous solutions [74].…”

Impact of freeze-thaw cycles on organic carbon and metals in waters of permafrost peatlands

“…and the second one in the permafrost zone (> 30-40 cm). Both subsamples represent oligotrophic peat composed of Sphagnum angustifolium, cotton-grass Eriophorum, Scheuchzeria palustris, bog-sedge Carex limosa, lichens, dwarf shrubs and some amount of wood debris (pine) and green mosses (Payandi-Rolland et al, 2020b). Ground vegetation contained mosses (Sphagnum fuscum and Sphagnum augustifolium) and lichens (Cladonia genus), which colonize hollows and mounds of the palsa and are reported to be widely spread species in the tundra (Malmer et al, 2005).…”

“…Ground vegetation contained mosses (Sphagnum fuscum and Sphagnum augustifolium) and lichens (Cladonia genus), which colonize hollows and mounds of the palsa and are reported to be widely spread species in the tundra (Malmer et al, 2005). Aqueous leachates were prepared by reacting 10 g of organic substrate (10 gwet for frozen peat and 10 gdry for vegetation) with 1 L of sterile MilliQ water under constant agitation (70 rpm) at 25 ± 2 °C in the dark and aerobic conditions (Payandi-Rolland et al, 2020b;Shirokova et al, 2017aShirokova et al, , 2017b. After 3 days of reactions, the suspension was centrifuged at 4500 g for 5 minutes and then sterile filtered (< 0.22 µm) using 500 mL Nalgene units and a manual vacuum pump.…”

“…The results of the present study demonstrated rather minor (i.e., ≤ 10%) effects of freeze-thaw cycles on DOC quantity and quality in various leachates of soils and vegetation which indicates strong stability of DOM in typical surface waters of boreal peatlands (except large river). As such, the FTC may be of sub-ordinary importance on DOM transformation in surface waters of permafrost peatlands relative to other biotic and abiotic factors such as heterotrophic degradation and photolysis (Payandi-Rolland et al, 2020b;L. S. Shirokova et al, 2019).…”

“…Transition periods (i.e. early spring and late autumn) appeared to be essential times for the export (Manasypov et al, 2015; and biodegradation (Payandi-Rolland et al, 2020b) of DOC in rivers and lakes of Arctic wetlands when the majority of DOC originates from leaching of supra-permafrost-soil and vegetation (Ma et al, 2019;Vonk et al, 2015). These periods are dominated by recurrent freeze-thaw cycles (FTC, Henry, 2008).…”