Waterlogging affects the mitigation of soil GHG emissions by biochar amendment in coastal wetland

Abstract

Emissions of greenhouse gases (GHGs) have greatly impacted the global warming by altering the composition of the atmosphere. The effect of biochar on GHG mitigation has been mainly studied in amended mineral soils and agricultural soils. However, the interactive effects of waterlogging and biochar application on GHG emissions, in coastal wetlands, are still poorly understood, which is important when considering the application of biochar at specific sites. We carried out a soil incubation experiment for 90 days at 25 °C to investigate the effects of two types of biochar (Phragmites communis and Spartina alterniflora) with different application rates (0%, 1%, 5%, and 10%) (w/w) on GHG emissions from soil at two different water levels (unwaterlogged and waterlogged soils). Furthermore, soil pH, organic carbon, nitrogen, and phosphorus contents were analyzed after incubation to gain insights into the underlying mechanisms of the biochar’s effects on CO2, CH4, and N2O evolution. Waterlogging significantly reduced the cumulative CO2 flux by 36.27%, had no effect on cumulative CH4 flux, and significantly increased cumulative N2O flux by 50.82%, and the corresponding global warming potential (GWP) significantly decreased by 29.72%. Biochar application reduced not only the cumulative CO2 flux, but also the cumulative CH4 absorption, which may shift soils from being CH4 sinks to sources. After biochar application, the cumulative N2O release increased from unwaterlogged soils but decreased in waterlogged soils. There was no significant difference between biochar type on GHG emissions, but differences were observed among different application rates. The GWP significantly decreased by 27.64–⁠69.39% and 36.11–87.34% after biochar application in the unwaterlogged and waterlogged soils, respectively. As a consequence, biochar application may significantly decrease GWP of soils due to the large reduction of CO2 release. These results suggest that biochar application is an effective way to reduce GWP in the Yellow River Delta Wetlands, especially when biochar is applied in waterlogged soils at high application rates.