Bacterial Response to Permafrost Derived Organic Matter Input in an Arctic Fjord

Abstract

The warming of the Arctic causes increased riverine discharge, coastal erosion, and the thawing of permafrost. Together, this is leading to an increased wash out of terrestrial dissolved organic matter (tDOM) into the coastal Arctic ecosystems. This tDOM may be anticipated to affect both carbon and nutrient flow in the microbial food web and microbial community composition, but there are few studies detailing this in Arctic marine ecosystems. We tested the effects of tDOM on the bacterial community composition and net-growth by extracting DOM from the active layer of permafrost soil and adding the aged tDOM concentrate to a natural microbial fjord community (Kongsfjorden, NW Svalbard). This resulted in an increased carbon load of 128 µM DOC in the tDOM treatment relative to the control of 83 µM DOC. We observed changes in community composition and activity in incubations already within 12 h where tDOM was added. Flow cytometry revealed that predominantly large bacteria increased in the tDOM treated incubations. The increase of this group correlated with the increase in relative abundance of the genus Glaciecola (Gammaproteobacteria). Glaciecola were initially not abundant in the bacterial community (0.6%), but their subsequent increase up to 47% after 4 days upon tDOM addition compared to 8% in control incubations indicates that they are likely capable of degrading permafrost derived DOM. Further, according to our experimental results we hypothesize that the tDOM addition increased bacterivorous grazing by small protists and thus tDOM might indirectly also effect higher trophic levels of the microbial food web.

Individual Physiological Adaptations Enable Selected Bacterial Taxa To Prevail during Long-Term Incubations

“…2 and 3) of marine and mesohaline enclosures toward Gammaproteobacteria has been observed in many other marine confinement experiments (3,5,19,26), although the gammaproteobacterial families dominating an enclosure will depend on the sample source. Thus, Stewart et al (6) and Müller et al (27) reported the dominance of Colwelliaceae, whereas Sipler et al (28) found mostly Oceanospirillaceae. Significant increases in Moraxellaceae (4) and Pseudoalteromonadaceae (29) have been reported from Baltic Sea enclosure experiments.…”

Microbial Abundance and Enzyme Activity Patterns: Response to Changing Environmental Characteristics along a Transect in Kongsfjorden (Svalbard Islands)

“…Kongsfjorden, characterized by Atlantic water influx and melting of tidal glaciers, is one of the most studied polar ecosystems; these features make it suitable as a study site to evaluate the impacts of climate variability and several studies have proliferated in this region over the last decade [51]. Climate change, with consequent global warming, is one emerging driver of change in the Arctic environments, causing glaciers' retreat, increased meltwater outflow, and riverine discharge [52]. In this context, understanding how the structure and functional diversity of the microbial community vary is a hot topic and a major challenge for future studies in aquatic polar microbiology [53].…”

“…Kongsfjorden, characterized by Atlantic water influx and melting of tidal glaciers, is one of the most studied polar ecosystems; these features make it suitable as a study site to evaluate the impacts of climate variability and several studies have proliferated in this region over the last decade [51]. Climate change, with consequent global warming, is one emerging driver of change in the Arctic environments, causing glaciers' retreat, increased meltwater outflow, and riverine discharge [52] In this context, understanding how the structure and functional diversity of the microbial community vary is a hot topic and a major challenge for future studies in aquatic polar microbiology [53]. Since microorganisms constitute the living basis of pelagic food webs and represent the drivers of carbon and nutrient cycling, the possible impacts of climate change in shaping the distribution and diversity of microbial communities is far more concerning, Arctic warming can potentially have severe consequences on large-scale microbial population dynamics, trophic-level interactions, and ecological processes driven by microbes.…”

Biological transformation of Arctic dissolved organic matter in a NE Greenland fjord

“…We therefore speculate that the BDOC method underestimates the in situ potential for degradation of visible FDOM. This method relies on long‐term incubations and as a result an altered bacterial community composition (Müller et al ) and function, which as a consequence likely reduces the ability to degrade visible FDOM. In contrast, the method applied here has a bacterial community more representative of natural conditions in the fjord and reveals their potential to degrade visible FDOM.…”