Temporal Changes in Soil Bacterial Diversity and Humic Substances Degradation in Subarctic Tundra Soil

Abstract

Humic substances (HS), primarily humic acids (HA) and fulvic acids (FA), are the largest constituent of soil organic matter. In microcosm systems with subarctic HS-rich tundra soil (site AK 1-75; approximately 5.6 °C during the thawing period) from Council, Alaska, the HA content significantly decreased to 48% after a 99-day incubation at 5 °C as part of a biologically mediated process. Accordingly, levels of FA, a putative byproduct of HA degradation, consistently increased to 172% during an identical incubation process. Culture-independent microbial community analysis showed that during the microcosm experiments, the relative abundance of phyla Proteobacteria (bacteria) and Euryarchaeota (archaea) largely increased, indicating their involvement in HS degradation. When the indigenous bacteria in AK 1-75 were enriched in an artificial mineral medium spiked with HA, the changes in relative abundance were most conspicuous in Proteobacteria (from 60.2 to 79.0%), specifically Betaproteobacteria-related bacteria. One hundred twenty-two HA-degrading bacterial strains, primarily from the genera Paenibacillus (phylum Firmicutes) and Pseudomonas (class Gammaproteobacteria), were cultivated from AK 1-75 and nearby sites. Through culture-dependent analysis with these bacterial isolates, we observed increasing HS-degradation rates in parallel with rising temperatures in a range of 0 °C to 20 °C, with the most notable increase occurring at 8 °C compared to 6 °C. Our results indicate that, although microbial-mediated HS degradation occurs at temperature as low as 5 °C in tundra ecosystems, increasing soil temperature caused by global climate change could enhance HS degradation rates. Extending the thawing period could also increase degradation activity, thereby directly affecting nearby microbial communities and rhizosphere environments.

Microbial Community of the Arctic Soil from the Glacier Foreland of Midtre Lovenbreen in Svalbard by Metagenome Analysis

“…2). This order of community composition is strongly comparable to that of the subarctic Alaskan tundra based on 454 pyrosequencing [22]. A previous study of the archaeal community structure of the active layer soil from Resolute in the Canadian High Arctic also supported our results, with Euryarchaeota acting as the major archaea group [12].…”

“…These two predominant phyla accounted for more than half of the total bacterial sequences. The bacterial community structure exhibited good consistency with the findings of previous studies showed that Proteobacteria and Actinobacteria were the dominant bacterial groups in Arctic soil samples [22,35]. DGGE analysis of an active layer from the Canadian high Arctic also showed that the dominant bands corresponded to Proteobacteria and Actinobacteria [31].…”

“…DGGE analysis of an active layer from the Canadian high Arctic also showed that the dominant bands corresponded to Proteobacteria and Actinobacteria [31]. A few previous studies reported that the metabolically versatile Actinobacteria, oligotrophic Acidobacteria, and widely distributed Bacteroidetes were dominant in Arctic tundra soils [15,22]. Several genera from the phylum Actinobacteria were detected in this study.…”

“…The Arctic environment is characterized by an extremely cold climate, short growing season, and limited nutrient supply [22]. For the last few decades, the arctic environment has been undergoing large changes because of increase in temperature caused by global warming, increased human activity and a wide-range of transport pollutants [14].…”

Complete genome sequence of a cold-adapted humic acid degrading bacterium Pedobacter sp. PAMC 27299 from the Antarctic seashore

“…: +82-31-670-4707;Fax: +82-31-675-1381 Antarctica seashore, extremely cold region, is the storage of huge amount of organic sources and mosses nearby seashore are great reservoir of humic substances through long-term accumulation by bacterial degradation in low rate (Park et al, 2015). Global warming lead to increasing of bacterial ability to degrade humic substances even in low temperatures and not only increase emission of carbon dioxide but also leach dissolved (Conesa et al, 2005) analyzing the best hits of the BLAST results.…”