Geology topics

Ruo He

Publications and source records attributed to Ruo He.

4 recordsLinked to original sources

USGS2020

Low O2 level enhances CH4-derived carbon flow into microbial communities in landfill cover soils

CH 4 oxidation in landfill cover soils plays a significant role in mitigating CH 4 release to the atmosphere. Oxygen availability and the presence of co-contaminants are potentially important factors affecting CH 4 oxidation rate and the fate of CH 4 -derived carbon. In this study, microbial populations that oxidize CH 4 and the subsequent conversion of CH 4 -derived carbon into CO 2 , soil organic C and biomass C were investigated in landfill cover soils at two O 2 tensions, i.e., O 2 concentrations of 21% (“sufficient”) and 2.5% (“limited”) with and without toluene. CH 4 -derived carbon was primarily converted into CO 2 and soil organic C in the landfill cover soils, accounting for more than 80% of CH 4 oxidized. Under the O 2 -sufficient condition, 52.9%–59.6% of CH 4 -derived carbon was converted into CO 2 (CE CO2-C ), and 29.1%–39.3% was converted into soil organic C (CE organic-C ). A higher CE organic-C and lower CE CO2-C occurred in the O 2 -limited environment, relative to the O 2 -sufficient condition. With the addition of toluene, the carbon conversion efficiency of CH 4 into biomass C and organic C increased slightly, especially in the O 2 -limited environment. A more complex microbial network was involved in CH 4 assimilation in the O 2 -limited environment than under the O 2 -sufficient condition. DNA-based stable isotope probing of the community with 13 CH 4 revealed that Methylocaldum and Methylosarcina had a higher relative growth rate than other type I methanotrophs in the landfill cover soils, especially at the low O 2 concentration, while Methylosinus was more abundant in the treatment with both the high O 2 concentration and toluene. These results indicated that O 2 -limited environments could prompt more CH 4 -derived carbon to be deposited into soils in the form of biomass C and organic C, thereby enhancing the contribution of CH 4 -derived carbon to soil community biomass and functionality of landfill cover soils (i.e. reduction of CO 2 emission).

Environmental Pollution↗

USGS2012

Diversity of active aerobic methanotrophs along depth profiles of arctic and subarctic lake water column and sediments

Methane (CH 4 ) emitted from high-latitude lakes accounts for 2–6% of the global atmospheric CH 4 budget. Methanotrophs in lake sediments and water columns mitigate the amount of CH 4 that enters the atmosphere, yet their identity and activity in arctic and subarctic lakes are poorly understood. We used stable isotope probing (SIP), quantitative PCR (Q-PCR), pyrosequencing and enrichment cultures to determine the identity and diversity of active aerobic methanotrophs in the water columns and sediments (0–25 cm) from an arctic tundra lake (Lake Qalluuraq) on the north slope of Alaska and a subarctic taiga lake (Lake Killarney) in Alaska's interior. The water column CH 4 oxidation potential for these shallow (~2m deep) lakes was greatest in hypoxic bottom water from the subarctic lake. The type II methanotroph, Methylocystis, was prevalent in enrichment cultures of planktonic methanotrophs from the water columns. In the sediments, type I methanotrophs (Methylobacter, Methylosoma and Methylomonas) at the sediment-water interface (0–1 cm) were most active in assimilating CH 4 , whereas the type I methanotroph Methylobacter and/or type II methanotroph Methylocystis contributed substantially to carbon acquisition in the deeper (15–20 cm) sediments. In addition to methanotrophs, an unexpectedly high abundance of methylotrophs also actively utilized CH 4 -derived carbon. This study provides new insight into the identity and activity of methanotrophs in the sediments and water from high-latitude lakes.

Alaska↗

USGS2012

Identification of functionally active aerobic methanotrophs in sediments from an arctic lake using stable isotope probing

Arctic lakes are a significant source of the greenhouse gas methane (CH 4 ), but the role that methane oxidizing bacteria (methanotrophs) play in limiting the overall CH 4 flux is poorly understood. Here, we used stable isotope probing (SIP) techniques to identify the metabolically active aerobic methanotrophs in upper sediments (0–1 cm) from an arctic lake in northern Alaska sampled during ice-free summer conditions. The highest CH 4 oxidation potential was observed in the upper sediment (0–1 cm depth) with 1.59 μmol g wet weight -1 day -1 compared with the deeper sediment samples (1–3 cm, 3–5 cm and 5–10 cm), which exhibited CH 4 oxidation potentials below 0.4 μmol g wet weight -1 day -1 . Both type I and type II methanotrophs were directly detected in the upper sediment total communities using targeted primer sets based on 16S rRNA genes. Sequencing of 16S rRNA genes and functional genes ( pmoA and mxaF ) in the 13 C-DNA from the upper sediment indicated that type I methanotrophs, mainly Methylobacter, Methylosoma, Methylomonas and Methylovulum miyakonense, dominated the assimilation of CH 4 . Methylotrophs, including the genera Methylophilus and/or Methylotenera, were also abundant in the 13 CDNA. Our results show that a diverse microbial consortium acquired carbon from CH 4 in the sediments of this arctic lake.

Alaska↗

USGS2012

Shifts in identity and activity of methanotrophs in arctic lake sediments in response to temperature changes

Methane (CH 4 ) flux to the atmosphere is mitigated via microbial CH 4 oxidation in sediments and water. As arctic temperatures increase, understanding the effects of temperature on the activity and identity of methanotrophs in arctic lake sediments is important to predicting future CH 4 emissions. We used DNA-based stable-isotope probing (SIP), quantitative PCR (Q-PCR), and pyrosequencing analyses to identify and characterize methanotrophic communities active at a range of temperatures (4°C, 10°C, and 21°C) in sediments (to a depth of 25 cm) sampled from Lake Qalluuraq on the North Slope of Alaska. CH 4 oxidation activity was measured in microcosm incubations containing sediments at all temperatures, with the highest CH 4 oxidation potential of 37.5 μmol g −1 day −1 in the uppermost (depth, 0 to 1 cm) sediment at 21°C after 2 to 5 days of incubation. Q-PCR of pmoA and of the 16S rRNA genes of type I and type II methanotrophs, and pyrosequencing of 16S rRNA genes in 13 C-labeled DNA obtained by SIP demonstrated that the type I methanotrophs Methylobacter , Methylomonas , and Methylosoma dominated carbon acquisition from CH 4 in the sediments. The identity and relative abundance of active methanotrophs differed with the incubation temperature. Methylotrophs were also abundant in the microbial community that derived carbon from CH 4 , especially in the deeper sediments (depth, 15 to 20 cm) at low temperatures (4°C and 10°C), and showed a good linear relationship ( R = 0.82) with the relative abundances of methanotrophs in pyrosequencing reads. This study describes for the first time how methanotrophic communities in arctic lake sediments respond to temperature variations.

Alaska↗