Abstract
The nitrogen (N) input and Spartina alterniflora invasion in the tidal marsh of the southeast of China are increasingly serious. To evaluate CH4 emissions in the tidal marsh as affected by the N inputs and S. alterniflora invasion, we measured CH4 emissions from plots with vegetated S. alterniflora and native Cyperus malaccensis, and fertilized with exogenous N at the rate of 0 (N0), 21 (N1) and 42 (N2) g N/(m2·yr), respectively, in the Shanyutan marsh in the Minjiang River estuary, the southeast of China. The average CH4 fluxes during the experiment in the C. malaccensis and S. alterniflora plots without N addition were 3.67 mg CH4/(m2·h) and 7.79 mg CH4/(m2·h), respectively, suggesting that the invasion of S. alterniflora into the Minjiang River estuary stimulated CH4 emission. Exogenous N had positive effects on CH4 fluxes both in native and in invaded tidal marsh. The mean CH4 fluxes of N1 and N2 treatments increased by 31.05% and 123.50% in the C. malaccensis marsh, and 63.88% and 7.55% in the S. alterniflora marsh, respectively, compared to that of N0 treatment. The CH4 fluxes in the two marshes were positively correlated with temperature and pH, and negatively correlated with electrical conductivity and redox potential (Eh) at different N addition treatments. While the relationships between CH4 fluxes and environmental variables (especially soil temperature, pH and Eh at different depths) tended to decrease with N additions. Significant temporal variability in CH4 fluxes were observed as the N was gradually added to the native and invaded marshes. In order to better assess the global climatic role of tidal marshes as affected by N addition, much more attention should be paid to the short-term temporal variability in CH4 emission.
Highlights
Human activities, primarily fertilizer application, fossil fuel combustion, land use change and development of industry and stock raising, have drastically increased the inputs of nitrogen (N) to stimulate plant growth, change species composition and diversity, and alter carbon (C) and N cycling rate in most ecosystems since the industrial revolution (Matson et al, 2002)
In the S. alterniflora marsh, the CH4 fluxes ranged from 2.02 mg CH4/(m2·h) to 18.42 mg CH4/(m2·h) and the mean value was 7.79 mg CH4/(m2·h), increased by 112.26% compared to the C. malaccensis marsh
We found that the mean CH4 fluxes increased by 31.05% (N1) and 123.50% (N2) in the C. malaccensis marsh, and 63.88% (N1) and 7.55% (N2) in the S. alterniflora marsh with the rates of 21 g NH4NO3-N/m2 and 42 g NH4NO3-N/m2 addition during the experiment, suggesting that the increased input of N to tidal marshes would increase the contribution of CH4 to the atmosphere
Summary
Primarily fertilizer application, fossil fuel combustion, land use change and development of industry and stock raising, have drastically increased the inputs of nitrogen (N) to stimulate plant growth, change species composition and diversity, and alter carbon (C) and N cycling rate in most ecosystems since the industrial revolution (Matson et al, 2002). High N input by human activities is of concern because it may alter the emission of greenhouse gases to the atmosphere and further contribute to global warming (Dalal and Allen, 2008; Liu and Greaver, 2009). Increasing N loading may have strong effects on CH4 emissions from the estuarine environments by influencing plant growth (Zhang et al, 2010), changing the biological and chemical properties of soils (Min et al, 2011), stimulating the microbial processes (Blagodatskaya et al, 2007; Inselsbacher et al, 2011). There is little known available data about the CH4 emission response to N additions in natural sub-tropical estuarine tidal marshes, such as those in the Minjiang River estuary, the southeast of China
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