Molecular Insights on Dissolved Organic Matter Transformation by Supraglacial Microbial Communities

Abstract

Snow overlays the majority of Antarctica and is an important repository of dissolved organic matter (DOM). DOM transformations by supraglacial microbes are not well understood. We use ultrahigh resolution mass spectrometry to elucidate molecular changes in snowpack DOM by in situ microbial processes (up to 55 days) in a coastal Antarctic site. Both autochthonous and allochthonous DOM is highly bioavailable and is transformed by resident microbial communities through parallel processes of degradation and synthesis. DOM thought to be of a more refractory nature, such as dissolved black carbon and carboxylic-rich alicyclic molecules, was also rapidly and extensively reworked. Microbially reworked DOM exhibits an increase in the number and magnitude of N-, S-, and P-containing formulas, is less oxygenated, and more aromatic when compared to the initial DOM. Shifts in the heteroatom composition suggest that microbial processes may be important in the cycling of not only C, but other elements such as N, S, and P. Microbial reworking also produces photoreactive compounds, with potential implications for DOM photochemistry. Refined measurements of supraglacial DOM and their cycling by microbes is critical for improving our understanding of supraglacial DOM cycling and the biogeochemical and ecological impacts of DOM export to downstream environments.

Hydrologic connectivity determines dissolved organic matter biogeochemistry in northern high‐latitude lakes

“…Past studies examining the impact of photochemistry on DOM composition found 70% of photoproduced or persistent molecular formulae contained N due to the selective removal of CHO molecular formulae (Rossel et al 2013). Similar increases in N-containing percentage of assigned formulae (45%) were observed by microbial reworking of DOM in supraglacial environments (Antony et al 2017). The lakes with the most enriched δ 18 O-H 2 O values had a similar CHON percentage of assigned molecular formulae as lakes on the Tibetan Plateau (43-49%), that have relatively long residence times and extensive exposure to photochemical irradiation at high elevation (Spencer et al 2014).…”

“…The relative abundance of CHON compounds correlated significantly with δ 18 O-H 2 O (r 2 = 0.41, p < 0.001) while CHOS and CHONS were very weakly correlated with δ 18 O-H 2 O (r 2 = 0.14, p = 0.006 and r 2 = 0.08, p = 0.034, respectively; Table 2). The increased relative abundance of CHON molecular formulae is related to the accumulation of nitrogen rich autochthonously produced DOM (D'Andrilli et al 2015;Antony et al 2017) or photochemical degradation of DOM selectively removing CHO molecular formulae (Stubbins et al 2010;Rossel et al 2013) in lakes that receive little allochthonous inputs (Fig. 4).…”

Ecological Stoichiometry of the Mountain Cryosphere

“…Supraglacial environments are typically nutrient poor (Figure 2; Table S1) and available nutrients are often present in organic forms (e.g., residues of microbial and/or plant cells, decayed organic matter, microbial exudates; Antony et al, 2017). For reference eutrophic lakes typically have total N concentrations of 650-1,200 µg L −1 and total P concentrations of 30-100 µg L −1 (Dodds and Whiles, 2010).…”

“…In general, supraglacial ecosystems accumulate organic matter through in situ primary production as well as deposition from terrestrial and anthropogenic sources Singer et al, 2012;Stibal et al, 2012; Figure 2). Both autochthonous and allochthonous dissolved organic matter (DOM) are actively transformed by microbial communities through degradation and synthesis (Antony et al, 2017). Through this microbial processing, low quality DOM (i.e., high C:N, C:P) can be processed and "upgraded" (converted to lower C:N and/or C:P), thereby becoming more bioavailable to heterotrophs both within and downstream of the supraglacial zone (Musilova et al, 2017).…”

Dissolved organic carbon in glaciers of the southeastern Tibetan Plateau: Insights into concentrations and possible sources

“…Glaciers accumulate organic OC from in situ primary production as well as from atmospheric deposition of carbonaceous material derived from terrestrial and anthropogenic inputs [ 1 , 15 ]. Anthropogenic combustion products are considered the main source of the aerosol organic carbon deposited on glacier surfaces [ 9 – 10 , 16 ].…”