Spatial Heterogeneity of Nitrogen Fixation and Denitrification in Streams
Document Type
Article
Publication Date
4-1-2025
Department
Department of Biological Sciences
Abstract
Stream ecosystems exhibit high degrees of spatial heterogeneity at nested scales from microhabitats to regions. This heterogeneity may facilitate the co-occurrence of biogeochemical processes that are favored under incompatible environmental conditions, like dinitrogen (N2 gas) fixation and denitrification. We hypothesized that environmental variation at the patch scale (1–10’s m) would facilitate the co-occurrence of N2 fixation and denitrification through the formation of hot spots. We measured rates of N2 fixation and denitrification and relative abundances of nifH and nirS (genes that encode for the enzymes nitrogenase and nitrite reductase, respectively) in patches determined by channel geomorphic units and substratum type in seven streams encompassing a gradient of N and P concentrations. We found hot spots, where rates of N2 fixation and denitrification were 1–4 times higher than reach-average rates, in all study streams. Most N2 fixation hot spots were in patches with rock substrata, while denitrification rates and relative abundances of nifH and nirS were higher in patches with fine sediment. Yet, in one of the streams, the same patches hosted rates in the top 25% of all patches for both denitrification and N2 fixation. Across all streams and patches, organic matter and dissolved oxygen concentrations were important predictors of rates of N2 fixation, denitrification, and nifH relative abundance, while P concentration was important to N2 fixation and denitrification. Our results demonstrate that understanding the spatial ecology of microbially driven nutrient cycling is required to characterize nutrient fluxes more completely in stream ecosystems.
Publication Title
Ecosystems
Recommended Citation
Eberhard, E. K.,
Techtmann, S.,
Baxter, C.,
&
Marcarelli, A.
(2025).
Spatial Heterogeneity of Nitrogen Fixation and Denitrification in Streams.
Ecosystems,
28(2).
http://doi.org/10.1007/s10021-025-00963-y
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p2/1438
