Invasive Spartina alterniflora can mitigate N₂O emission in coastal salt marshes

Although there are studies on nitrous oxide (N₂O) fluxes in coastal salt marshes, temporal and spatial variations of this greenhouse gas are still uncertain. Especially salt marshes of the East China Sea coast covered by invasive Spartina alterniflora have shown controversial results. To analyse seasonal patterns of N₂O fluxes and their relationship with environmental factors, three plots dominated by S. alterniflora, and differing in sediment salinity and vegetation history (P1, P2, P3), and one bare mudflat (P0) in a salt marsh of Nanhui shore in the southern fringe of Yangtze River estuary have been established. Monthly studies from March 2017 to January 2018 using a chamber technique showed that average N₂O fluxes from all four plots ranged from −41.9 to 39.3 μg N₂O·m⁻²·h⁻¹, whereas average flux (4.2 μgN₂O·m⁻²·h⁻¹) in P1, P2 and P3 was not significantly different from that measured in P0 (1.3 μgN₂O·m⁻²·h⁻¹). There was a clear seasonal difference: in spring and summer, all the sites showed slight emission while consumption prevailed in autumn and winter. In vegetated sites this trend was more remarkable than in the bare mudflat. N₂O flux showed positive correlation (p < .05) with air and sediment temperature, and plant development (height of vegetation). Nitrate was not the limiting factor of N₂O emission in the Yangtze estuary. In the salt marsh where vegetation community was mature, higher sediment salinity reduced N₂O emission (P1 < P2) by influencing other environmental factors such as total carbon (TC), total nitrogen (TN) content and sediment texture. In comparison with other tidal macrophytes S. alterniflora showed relatively low N₂O emission. Therefore, it can be considered as a species for tidal zone stabilisation.