Abstract
Typhoons can alter carbon cycling by increasing carbon inputs and by the oceanic water intrusion at low latitudes. Our understanding of how typhoons impacts C and N cycles by reflecting combine and separate effects of elevated salinity and carbon enrichment is poor. We conducted a mesocosm experiment simulating the effect of a salinity of 10‰ and dissolved organic carbon (DOC) enrichment of the surface water with acetate as DOC source on the dynamics of porewater nutrients and the emissions of carbonaceous greenhouse gases using plants and soil system from a Cyperus malaccensis freshwater wetland in the Min River estuary, southeastern China. The concentrations of NH4+-N and NO3−-N in porewater rose under elevated salinity but decreased with DOC enrichment, salinity and DOC in combination acted antagonistically such that there was no effect compared to the control. A 10‰ increase in salinity increased the cumulative CO2 emissions (+29%) and decreased the cumulative CH4 emissions (−61%) during the growing season. In response to DOC, The cumulative emissions of CO2 and CH4 increased by 79% and 84%, respectively. In response to the combined elevated salinity and DOC enrichment, the cumulative emissions of CO2 increased by 69% and cumulative methane emissions increased by 44%. Elevated salinity plus DOC enrichment decreased the activity of the N-cycling enzyme β-1,4-N-acetylglucosaminidase, but increased the activities of two C-cycling enzymes (β-1,4-glucosidase and 1,4-β-cellobiosidase) and the P-cycling enzyme acid phosphatase, indicating a higher demand for C and P relative to N. The combination of increased C as CO2 in all cases, increased CH4 only in the case of DOC addition, and rising inorganic N fluxes only in the case of salt suggeated that elevated salinity and DOC enrichment induced by typhoons may thus accelerate the release of C but have little influence on N release from tidal freshwater wetland ecosystems.
Highlights
Coastal wetlands occupy 5.7 × 106 km2 globally (Mitsch and Gosselink 2007, Ramsar Convention Secretariat 2013) and 1.2 × 104 km2 in China (Shen and Zhu 1999, Huang et al 2006)
The effects of strong tropical storms on the production and decomposition of litter in ecosystems have been studied in several forests, with no consensus on the rates of litter decomposition
Studying changes in C, N and P stoichiometry during litter decomposition can advance our understanding of the relationships among litter decomposition rate and the interactions of various nutrients in the plant-litter-soil system (Manzoni et al 2010)
Summary
Remaining litter generally increased its N:P ratio during decomposition. The soil was enriched with organic matter and nutrients for several months, which should favor microbial growth rates (higher C, N and P availability and lower C: nutrient and N:P ratios) and increase the rates of C and nutrient cycling. If the frequency and/or intensity of typhoons increase, a constant increase in the release of N and P to the soil with lower N:P ratios could change the N and P cycles in wetlands and provide better conditions for the spread of fastgrowing species
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