Filtration artefacts in bacterial community composition can affect the outcome of dissolved organic matter biolability assays

Abstract

Abstract. Inland waters are large contributors to global carbon dioxide (CO2) emissions, in part due to the vulnerability of dissolved organic matter (DOM) to microbial decomposition and respiration to CO2 during transport through aquatic systems. To assess the degree of this vulnerability, aquatic DOM is often incubated in standardized biolability assays. These assays isolate the dissolved fraction of aquatic OM by size filtration prior to incubation. We test whether this size selection has an impact on the bacterial community composition and the consequent dynamics of DOM degradation using three different filtration strategies: 0.2 µm (filtered and inoculated), 0.7 µm (generally the most common DOM filter size) and 106 µm (unfiltered). We found that bacterial community composition, based on 16S rRNA amplicon sequencing, was significantly affected by the different filter sizes. At the same time, the filtration strategy also affected the DOM degradation dynamics, including the δ13C signature. However, the dynamics of these two responses were decoupled, suggesting that filtration primarily influences biolability assays through bacterial abundance and the presence of their associated predators. By the end of the 41-day incubations all treatments tended to converge on a common total DOM biolability level, with the 0.7 µm filtered incubations reaching this point the quickest. These results suggest that assays used to assess the total biolability of aquatic DOM should last long enough to remove filtration artefacts in the microbial population. Filtration strategy should also be taken into account when comparing results across biolability assays.

Weak mineralization despite strong processing of dissolved organic matter in Eastern Arctic tundra ponds

“…It is worth mentioning that some of the divergence among studies could also be linked to variations in the definition of lability and in the chosen experimental setup. For example, variable filtration efficiencies in removing microbes or variable incubation lengths can lead to differing microbial regrowth or taxonomic composition that can affect the outcome of lability assays (Dean et al 2018).…”

Stream Dissolved Organic Matter in Permafrost Regions Shows Surprising Compositional Similarities but Negative Priming and Nutrient Effects

“…Incubations were done in the dark at room temperature (20°C), constraining DOC loss to biotic rather than photic processes. The relatively coarse filtration (0.7‐μm effective pore size) prior to incubation allowed ambient aquatic microorganisms to pass through the filter into the incubation bottles and mineralize the DOC (Dean et al, 2018; Larouche et al, 2015; Vonk, Tank, Mann, et al, 2015). Treatments were added only at the start of the incubations to simulate mixing of permafrost thaw products with modern DOM in stream networks (Abbott et al, 2015; Drake et al, 2015; Shogren et al, 2019; Tanski et al, 2017).…”

Seasonal variability in particulate organic carbon degradation in the Kolyma River, Siberia

“…Alternatively, filtration may change (a) the composition of the microbial pool through exclusion of predators of bacteria and/or (b) the composition of the DOC pool (e.g. through lysis) thus enhancing degradation of DOC in the filtered incubations relative to wholewater incubations [74].…”