Nitrogen substrate–dependent nitrous oxide cycling in salt marsh sediments

Abstract

Nitrous oxide (N2O) is important to Earth's climate because it is a strong absorber of radiation and an important ozone depletion agent. Increasing anthropogenic nitrogen input into the marine environment, especially to coastal waters, has led to increasing N2O emissions. Identifying the nitrogen compounds that serve as substrates for N2O production in coastal waters reveals important pathways and helps us understand their control by environmental factors. In this study, sediments were collected from a long-term fertilization site in Great Sippewissett Marsh, Falmouth, Massachusetts. The 15N tracer incubation time course experiments were conducted and analyzed for potential N2O production and consumption rates. The two nitrogen substrates of N2O production, ammonium and nitrate, correspond to the two production pathways, nitrification and denitrification, respectively. When measurable nitrate was present, despite ambient high ammonium concentrations, denitrification was the major N2O production pathway. When nitrate was absent, ammonium became the dominant substrate for N2O production, via nitrification and coupled nitrification-denitrification. Net N2O consumption was enhanced under low oxygen and nitrate conditions. N2O production and consumption rates increased with increasing levels of nitrogen fertilization in long-term experimental plots. These results indicate that increasing anthropogenic nitrogen input to salt marshes can stimulate sedimentary N2O production via both nitrification and denitrification, whereas episodic oxygen depletion results in net N2O consumption.

Estuaries as Sources and Sinks of N2O Across a Land Use Gradient in Subtropical Australia

“…Although estuaries are generally assumed to be an N 2 O source, undersaturated surface waters are reported for both areas receiving low N inputs (Liu et al, ; Soued et al, ) and those receiving high enough N inputs to drive the O 2 depletion that triggers denitrification (Borges et al, ; Ji et al, ; Punshon & Moore, ). Here the estuary mouths, which tended to be low in inorganic N and supersaturated in DO, were the most consistent N 2 O sinks.…”

Long‐term fertilization alters the relative importance of nitrate reduction pathways in salt marsh sediments

“…The Great Sippewissett Marsh is limited by N as shown by a comprehensive study on its N budget [ Valiela and Teal , ]. In the experimental plots receiving long‐term fertilization, enhanced primary production, nutrient retention, organic N content, N 2 production, and nitrous oxide production have been documented [ Valiela et al ., , ; Hamersley and Howes , ; Brin et al ., ; Kinney and Valiela , ; Uldahl , ; Ji et al ., ]. These previous studies showed that the various effects of long‐term fertilization were usually more pronounced in extra‐high‐fertilization (XF) plots than in high‐fertilization (HF) plots.…”

“…NH 4 + and NO 3 − concentrations in pore water samples were determined as described previously [ Ji et al ., ]. In brief, NO 3 − concentrations were measured in duplicate using a hot (90°C) acidified vanadium (III) reduction column coupled to a Teledyne Chemiluminescence NO/NO x Analyzer (Model 200E), with a detection limit of 0.5 μM [ Braman and Hendrix , ; Garside , ].…”

“…Anammox rates were assumed to contribute a negligible fraction of N 2 production [ Koop‐Jakobsen and Giblin , ]. Although nitrous oxide production was not included in this model, denitrification rates were unlikely underestimated, because nitrous oxide production rates were generally lower than or similar to consumption rates measured at the same site [ Ji et al ., ].…”

Systems biology approaches towards predictive microbial ecology

“…These studies in the OMZ have also revealed a remarkable richness of metabolic processes along the redox gradient, as well as novel linkages between community members (Plominsky et al, 2018). Furthermore, stable isotope studies have provided enormous insight into understanding spatio-temporal patterns of production and consumption of different nitrogen species in the OMZ (Sun et al, 2017;Ji et al, 2015a). In these areas, the production of N 2 O varies regionally (Ji et al, 2015b) and seasonally (Farías et al, 2015;Torres-Beltrán et al, 2017;Capelle et al, 2018).…”