Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones

Abstract

Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (Sr: 0.63 ± 0.02 and SUVA254: 1.65 ± 0.06 L mg C−1 m−1 & Sr: 0.68 ± 0.01 and SUVA254: 1.17 ± 0.06 L mg C−1 m−1, respectively) compared to the lacustrine soil type (Sr: 0.71 ± 0.02 and SUVA254: 2.15 ± 0.05 L mg C−1 m−1). The difference in composition of DOM leads to the development of three different microbial communities. Whereas Alphaproteobacteria dominate in fluvial and lacustrine deposit types (67 and 87% relative abundance, respectively), Gammaproteobacteria is the most abundant class for moraine deposit type (88% relative abundance). Bacterial growth efficiency (BGE) is 66% for DOM from moraine deposit type, while 13 and 28% for DOM from fluvial and lacustrine deposit types, respectively. The three microbial communities therefore differ strongly in their net effect on DOM utilization depending on the eroded landscape type. The high BGE value for moraine-derived DOM is probably caused by a larger proportion of labile colorless DOM. These results indicate that the substrate controls marine microbial community composition and activities in coastal waters. This suggests that biogeochemical changes in the Arctic coastal zone will depend on the DOM character of adjacent deposit types, which determine the speed and extent of DOM mineralization and thereby carbon channeling into the microbial food web. We conclude that marine microbes strongly respond to the input of terrestrial DOM released by coastal erosion and that the landscape type differently influence marine microbes.

Substrate diversity affects carbon utilization rate and threshold concentration for uptake by natural bacterioplankton communities

“…For this experiment it is also important to keep in mind that the bacterial community composition was significantly different between treatments. This concurs with previous studies showing that bacterial communities are tightly coupled to the concentration and composition of DOM (Cottrell & Kirchman 2000, Kirchman et al 2004, Judd et al 2006, Alonso-Sáez & Gasol 2007, Amaral et al 2016, Broman et al 2019, Bruhn et al 2021.…”

Shifting stoichiometry: Long‐term trends in stream‐dissolved organic matter reveal altered C:N ratios due to history of atmospheric acid deposition

“…This finding suggests that the adsorption to silt particles can influence DOM availability by controlling the long‐term storage and export of DOC and DON (Dosskey & Bertsch, 1997 ; Kaiser & Guggenberger, 2000 ). The higher trends of DOC and DON in moraine sites (Figure S5 ) could be due to greater OM availability and associated microbial decomposition activity (Bruhn et al, 2021 ). Collectively, the results of these models support the hypothesis that regional state factors such as geology and soil type are important controls of stream long‐term DOM trends.…”

“…This finding suggests that the adsorption to silt particles can influence DOM availability by controlling the long-term storage and export of DOC and DON (Dosskey & Bertsch, 1997;Kaiser & Guggenberger, 2000). The higher trends of DOC and DON in moraine sites (Figure S5) could be due to greater OM availability and associated microbial decomposition activity (Bruhn et al, 2021).…”

Climate warming-driven changes in the flux of dissolved organic matter and its effects on bacterial communities in the Arctic Ocean: A review

“…Autochthonous 162-640 µM (Retelletti Brogi et al, 2018) -LMW compounds (<350 Da) (e.g., amino acids and glucose) and protein-like substances (Muller et al, 2013;Jorgensen et al, 2015;Retelletti Brogi et al, 2018;Retelletti Brogi et al, 2019;Piontek et al, 2021); Thawed permafrost soil Allochthonous Autochthonous 998 ± 27 µM (Ward and Cory, 2015) -Amino acids, protein, peptides, aliphatic components, and carbohydrates (Ward and Cory, 2015;Heslop et al, 2019;Bruhn et al, 2021;MacDonald et al, 2021);…”