“Iron – Cold Iron – is Master of them all”: Consequences of microbial iron-reduction for soil organic matter in coastal Arctic tundra
Ted
K.
Raab, Stanford University, Dept. of Biology, tkraab@stanford.edu
(Presenting)
David
A.
Lipson, San Diego State University, Dept. of Biology, dlipson@sciences.sdsu.edu
Largus
T.
Angenent, Cornell University, Dept. of Biological and Environmental Engineering, la249@cornell.edu
Coastal arctic tundra is a significant landscape unit above 65o N, and in the absence of significant nitrate, sulfate, or manganese, these wet frozen soils have few electron acceptors readily available to support microbial respiration. Using a variety of soil chemical, molecular biological and electrochemical techniques, we seek to identify the importance of iron reduction in permafrost-affected soils near Barrow, AK. During significant portions of the snow/ice-free season, water-logged peat soils demonstrated sub-oxic redox potentials, and essentially no O2-availability below a few mm from the top of the profile. Minimum-tension microlysimeters (PTFE and iron-free) were deployed along three replicate transects along the Barrow Environmental Observatory boardwalks, and filtered soil-pore water was collected at 0-5 cm and 5-15 cm depths. We filtered and acidified standing water from early June-Sept 2009. Fluorescence spectroscopy was used to monitor seasonal patterns in DOC composition, and several fluorescence features from 440-520 nm became less evident as the soils warmed. HPLC of the microlysimeter samples demonstrated that oxalic acid, and to a lesser extent malate , are the predominant low-MW organic acids (that might act as e- acceptors for microbial respiration) in the soil solution. Replicate soil cores were collected to a depth of 50 cm, and split into five evenly-spaced horizons. We employed infrared spectroscopy and (C-1s, N-1s, and Fe-2p) x-ray photoelectron spectroscopy to quantify the electronic states of SOM at various depths in the soil cores. IR suggested that wetter sites were enriched for aromatic C. As a function of depth, N levels dropped-off more quickly than C with depth in XPS profiles, and the valences of soil C varied greatly with depth in the profiles. At a depth of 15-25 cm, we encountered loess-like materials, with consequently stronger Al/Si contents (from wide XPS scans). We are in the process of identifying possible sources for this material, as well as the balance of aeolian and cryo-turbation necessary to create these lenses. Finally, we are installing real-time bioelectrochemical system to monitor the activity of microbes that can respire solid electron acceptors.
Presentation Type: Poster
Poster Session: Carbon Cycle Science
NASA TE Funded Awards Represented:
NONE: Related Activity or Previously Funded TE Award