Methanogens Are Major Contributors to Nitrogen Fixation in Soils of the Florida Everglades

Abstract

The objective of this study was to investigate the interaction of the nitrogen (N) cycle with methane production in the Florida Everglades, a large freshwater wetland. This study provides an initial analysis of the distribution and expression of N-cycling genes in Water Conservation Area 2A (WCA-2A), a section of the marsh that underwent phosphorus (P) loading for many years due to runoff from upstream agricultural activities. The elevated P resulted in increased primary productivity and an N limitation in P-enriched areas. Results from quantitative real-time PCR (qPCR) analyses indicated that the N cycle in WCA-2A was dominated by and/, with an increasing trend in copy numbers in P-impacted sites. Many sequences (6 to 44% of the total) and transcript sequences (2 to 49%) clustered with the methanogenic , in stark contrast to the proportion of core gene sequences representing (≤0.27% of SSU rRNA genes) for the WCA-2A microbiota. Notably, archaeal gene transcripts were detected at all sites and comprised a significant proportion of total transcripts obtained from the unimpacted site, indicating that methanogens are actively fixing N Laboratory incubations with soils taken from WCA-2A produced transcripts with the production of methane from H plus CO and acetate as electron donors and carbon sources. Methanogenic N fixation is likely to be an important, although largely unrecognized, route through which fixed nitrogen enters the anoxic soils of the Everglades and may have significant relevance regarding methane production in wetlands. Wetlands are the most important natural sources of the greenhouse gas methane, and much of that methane emanates from (sub)tropical peatlands. Primary productivity in these peatlands is frequently limited by the availability of nitrogen or phosphorus; however, the response to nutrient limitations of microbial communities that control biogeochemical cycling critical to ecosystem function may be complex and may be associated with a range of processes, including methane production. We show that many, if not most, of the methanogens in the peatlands of the Florida Everglades possess the gene and actively express it for N fixation coupled with methanogenesis. These findings indicate that archaeal N fixation would play crucial role in methane emissions and overall N cycle in subtropical wetlands suffering N limitation.

The influence of oxygen and methane on nitrogen fixation in subarctic Sphagnum mosses

“…Although methanotrophs comprised less than 0.1% of the 16S rRNA, this alone does not exclude them from being a major contributor to N 2 fixation. Recently Bae et al ( 2018 ) showed that archaea constituting only 0.27% of the microbial community could account for 44% of the N fixed in an Florida peat system. In addition, N 2 fixation rates may differ over seasons (Lett and Michelsen 2014 ) and thus the microbial guilds actively performing N 2 fixation may vary with season.…”

The Saltpan Microbiome Is Structured by Sediment Depth and Minimally Influenced by Variable Hydration

“…Increased sulfate reduction in response to saltwater intrusion is a common phenomenon [97] and may help to explain the high potential for nitrogen fixation observed in saltpan sediments, as nitrogen fixation can be coupled to sulfate reduction [98][99][100]. Some Euryarchaeota are also able to fix nitrogen and are beginning to be recognized for their contribution to organic nitrogen supply in soils [101]. These unexpected differences in potential energy and nutrient flows between saltpans and brackish and fresh marsh underscore the inferential nature of the current methods and imply that further functional as well as taxonomic investigation of saltpan sediments are warranted.…”

Microbial resistance and resilience in response to environmental changes under the higher intensity of human activities than global average level

“…A melt curve analysis was conducted by increasing the temperature from 60 to 95°C by 0.5°C increments to verify the nonspecific amplification. The calculation of archaeal and bacterial amoA genes in the samples was based on a standard curve generated using standard plasmid DNA, which was made by cloning the target gene fragment as described by Bae, Morrison, Chanton, and Ogram (). The R 2 of qPCR standard curves was ≥.99, and the efficiency ( E ) was 84%–98% for AOA and 83%–90% for AOB, as calculated from the slope of the standard curve using the formula E = 10 (−1/slope) − 1.…”