Gross nitrous oxide production drives net nitrous oxide fluxes across a salt marsh landscape

Abstract

Sea level rise will change inundation regimes in salt marshes, altering redox dynamics that control nitrification - a potential source of the potent greenhouse gas, nitrous oxide (N2 O) - and denitrification, a major nitrogen (N) loss pathway in coastal ecosystems and both a source and sink of N2 O. Measurements of net N2 O fluxes alone yield little insight into the different effects of redox conditions on N2 O production and consumption. We used in situ measurements of gross N2 O fluxes across a salt marsh elevation gradient to determine how soil N2 O emissions in coastal ecosystems may respond to future sea level rise. Soil redox declined as marsh elevation decreased, with lower soil nitrate and higher ferrous iron in the low marsh compared to the mid and high marshes (P < 0.001 for both). In addition, soil oxygen concentrations were lower in the low and mid-marshes relative to the high marsh (P < 0.001). Net N2 O fluxes differed significantly among marsh zones (P = 0.009), averaging 9.8 ± 5.4 μg N m(-2) h(-1) , -2.2 ± 0.9 μg N m(-2) h(-1) , and 0.67 ± 0.57 μg N m(-2) h(-1) in the low, mid, and high marshes, respectively. Both net N2 O release and uptake were observed in the low and high marshes, but the mid-marsh was consistently a net N2 O sink. Gross N2 O production was highest in the low marsh and lowest in the mid-marsh (P = 0.02), whereas gross N2 O consumption did not differ among marsh zones. Thus, variability in gross N2 O production rates drove the differences in net N2 O flux among marsh zones. Our results suggest that future studies should focus on elucidating controls on the processes producing, rather than consuming, N2 O in salt marshes to improve our predictions of changes in net N2 O fluxes caused by future sea level rise.

Net soil–atmosphere fluxes mask patterns in gross production and consumption of nitrous oxide and methane in a managed ecosystem

“…This relationship was also observed in a managed grassland with high soil mineral N concentrations and net soil N 2 O emissions , but not in a salt marsh with low mineral N availability where net N 2 O uptake by soil occurred (Yang and Silver, 2016). The strong relationship between N 2 O production and reduction may have driven the well-constrained N 2 O yields in both this study and the managed grassland study because N 2 O reduction increased proportionally to N 2 O production rates.…”

Gross N2O Production Process, Not Consumption, Determines the Temperature Sensitivity of Net N2O Emission in Arable Soil Subject to Different Long-Term Fertilization Practices

“…By contrast, the gross consumption of NPK treatment was little affected by the imposed temperature at most of measuring time points, while its gross production rate exhibited a sheer increase with temperature at Days 15 and 30, resulting in an abrupt net N 2 O emission peak at Day 15 under 35 • C. These response patterns of gross production and consumption to temperature led to their varying correlations with net N 2 O emission rates: the gross production correlated significantly with net N 2 O emission rates across all fertilization treatments, while a significant correlation between gross N 2 O consumption rate and net N 2 O emission was only established in CT treatment. Taken together, our findings underscored an overarching role of gross N 2 O production in regulating N 2 O emission TS in the tested soil, thus echoing the emerging viewpoint that the variation of net N 2 O emission is primarily driven by the gross production rather than the consumption process (Yang and Silver, 2016;Wen et al, 2017).…”

Nitrous oxide emissions could reduce the blue carbon value of marshes on eutrophic estuaries

“…They recorded higher N 2 O flux from the grazed soil. Yang and Silver (2016) found positive and negative N 2 O fluxes in three zones of a salt marsh on California's Tomales Bay watershed where cattle grazing was a source of NO 3 − -N. However, we have found no single field study that compares marshes on multiple eutrophic estuaries or eutrophic systems to a comparable system without excessive nutrient availability.…”