Nitrogen fixation facilitates stream microbial mat biomass across the McMurdo Dry Valleys, Antarctica

Nitrogen (N) fixation is a fundamental mechanism by which N enters streams. Yet, because of modern N saturation, it is difficult to study the importance of N-fixation to stream nutrient budgets. Here, we utilized relatively simple and pristine McMurdo Dry Valley streams to investigate the role of N-...

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Bibliographic Details
Published in:Biogeochemistry
Main Authors: Kohler, Tyler J., Singley, Joel G., Wlostowski, Adam N., McKnight, Diane M.
Format: Text
Language:unknown
Published: DOCS@RWU 2023
Subjects:
Biofilm
C
Cyanobacteria
Hyporheic zone
MCM LTER
Mineralization
N
P biogeochemistry
Marine and Biological Research
Biology
McMurdo Dry Valleys
Antarc*
Antarctica
Online Access:https://docs.rwu.edu/fcas_fp/1024
https://doi.org/10.1007/s10533-023-01069-0
Description
Summary:Nitrogen (N) fixation is a fundamental mechanism by which N enters streams. Yet, because of modern N saturation, it is difficult to study the importance of N-fixation to stream nutrient budgets. Here, we utilized relatively simple and pristine McMurdo Dry Valley streams to investigate the role of N-fixing Nostoc abundance, streamwater dissolved inorganic N (DIN) concentration, and distance from the source glacier in regulating the elemental and isotopic composition of three microbial mat types (black, orange, and green) at the landscape scale. We found Nostoc-based black mats were the most enriched in δ15N, and δ15N signatures of mats increased where Nostoc was abundant, but did not surpass the atmospheric standard (δ15N ≈ 0‰). Furthermore, green and orange mat δ15N signatures became more depleted with increasing DIN, indicating that mats utilize glacial meltwater-sourced N when available. The distance from the source glacier explained limited variability in mat δ15N across sites, indicating the influence of individual stream characteristics on N spiraling. To further explore longitudinal N spiraling processes generating observed δ15Ν patterns, we developed a simple steady-state mathematical model. Analysis of plausible scenarios with this model confirmed that streams both have the capacity to remove allochthonous DIN over the plausible range of inputs, and that internal N sources are required to account for δ15N signatures and observed DIN concentrations at stream outlets. Collectively, these data and modeling results demonstrate that N-fixation exerts substantial influence within and across these streams, and is presumably dependent upon interconnected organic matter reserves, mineralization rates, and geomorphology.

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