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Abstract
Here we examined the impact of a commonly employed method used to measure nitrogen fixation, the acetylene reduction assay (ARA), on a marine sediment community. Historically, the ARA technique has been broadly employed for its ease of use, in spite of numerous known artifacts. To gauge the severity of these effects in a natural environment, we employed high-throughput 16S rRNA gene sequencing to detect differences in acetylene-treated sediments vs. non-treated control sediments after a 7 h incubation. Within this short time period, significant differences were seen across all activity of microbes identified in the sediment, implying that the changes induced by acetylene occur quickly. The results have important implications for our understanding of marine nitrogen budgets. Moreover, because the ARA technique has been widely used in terrestrial and freshwater habitats, these results may be applicable to other ecosystems.
Highlights
Every sampling effort and each experimental design impacts the environment and the processes we wish to measure
Net N2 Fluxes and N-Fixation Estimates The net N2 flux across the sediment water-interface was quantified to determine if the sediments were net denitrifying or net nitrogen fixing
Net N2 fluxes across the sediment-water interface for the individuals cores ranged from −10 to 28.6 μmol N2N m−2 h−1, suggesting that both N-fixation and denitrification were occurring (Table 1)
Summary
Every sampling effort and each experimental design impacts the environment and the processes we wish to measure. High-throughput 16S rRNA gene-based bacterial community surveys provide a powerful mechanism for us to examine the impact of commonly employed geochemical methods on the microbial population. Of particular interest to many aquatic biogeochemists is the microbially-mediated process of nitrogen fixation (N-fixation), which converts inert dinitrogen (N2) gas to biologically reactive nitrogen (N). While Earth’s atmosphere is comprised primarily of N2 gas, most organisms cannot tap into this reservoir. N-fixation provides critical links between biological organisms, this unreactive N pool, and N concentrations in the environment. The ability to fix N2 provides a significant advantage to organisms with this capability. Once N is fixed, various processes transform reactive N until it is returned to the atmosphere through denitrification. Because N is an essential and often limiting nutrient for primary productivity, its availability, at least in part, constrains global primary productivity (Tyrrell, 1999; Elser et al, 2007)
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