Response of methane emission to invasion of Spartina alterniflora and exogenous N deposition in the coastal salt marsh

Abstract

Listen

Translate article

Spartina alterniflora exhibits great invading potential in the coastal marsh ecosystems. Also, nitrogen (N) deposition shows an apparent increase in the east of China. To evaluate CH 4 emissions in the coastal marsh as affected by the invasion of S. alterniflora and N deposition, we measured CH 4 emission from brackish marsh mesocosms vegetated with S. alterniflora and a native plant, Suaeda salsa, and fertilized with exogenous N at the rates of 0 and 2.7 g N m −2, respectively. Dissolved porewater CH 4 concentration and redox potentials in soils as well as aboveground biomass and stem density of plants were also monitored. The averaged rate of CH 4 emission during the growing season in the S. alterniflora and S. salsa mesocosms without N application was 0.88 and 0.54 mg CH 4 m −2 h −1, respectively, suggesting that S. alterniflora plants significantly increased CH 4 emission mainly because of higher plant biomass rather than stem density compared to S. salsa, which delivered more substrates to the soil for methanogenesis. Exogenous N input dramatically stimulated CH 4 emission by 71.7% in the S. alterniflora mesocosm. This increase was attributable to enhancement in biomass and particularly stem density of S. alterniflora driven by N application, which transported greater photosynthesis products than oxygen into soils for CH 4 production and provided more pathways for CH 4 emission. In contrast, there was no significant effect of N fertilization on CH 4 emission in the S. salsa mesocosm. Although N fertilization significantly stimulated CH 4 production by increasing S. salsa biomass, no significant increase in stem density was observed. This fact, along with the low gas transport capacity of S. salsa, failed to efficiently transport CH 4 from wetlands into the atmosphere. Thus we argue that the stimulatory or inhibitory effect of N fertilization on CH 4 emission from wetlands might depend on the gas transport capacity of plants and their relative contribution to substrates for CH 4 production and oxygen for CH 4 oxidation in soil.