Exotic Spartina alterniflora invasion alters soil nitrous oxide emission dynamics in a coastal wetland of China

Abstract

Exotic Spartina alterniflora invasion resulting from anthropogenic activities significantly affects microbial nitrogen (N) transformation and associated nitrous oxide (N2O) emission in coastal wetland soils. However, the responses of soil N2O emission dynamics to plant invasion remain unclear. This study assesses the effects of S. alterniflora invasion on soil N2O potential production and consumption processes. We used natural isotope tracing technique to investigate potential N2O production and consumption rates in S. alterniflora invaded and native saltmarsh zones (Phragmites australis, Scirpus mariqueter and bare mudflat) in the Yangtze Estuary. Soil potential net N2O production rates in summer were lower in S. alterniflora stands than in S. mariqueter and bare mudflat stands, but no significant differences among these saltmarsh habitats occurred during winter. Potential gross N2O production and consumption rates were higher in S. alterniflora and P. australis stands compared to S. mariqueter and bare mudflat stands. The gross consumption proportion in S. alterniflora and P. australis stands was higher, which affected net N2O production. Hydroxylamine (NH2OH) oxidation and nitrifier denitrification contributed 4.52–12.62% and 13.87–21.58% of soil N2O source, respectively, but denitrification was the dominant pathway (69.83–80.09%). S. alterniflora invasion increased the contributions of NH2OH oxidation and nitrifier denitrification to N2O source slightly, but decreased the contribution of denitrification to N2O source. Soil potential N2O production and consumption processes were influenced by water-filled pore space, pH, sulfide, and carbon and N substrates. Exotic S. alterniflora invasion affected soil N2O dynamics by increasing substrates and altering microenvironments, thus mediating N2O emission from coastal saltmarsh soils.