Change in soil greenhouse gas fluxes with tidal pattern in a mangrove forest in Jiulong River Estuary in summer

Mangrove soils are potential sources of greenhouse gases, including carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), and their fluxes are highly related to environmental factors. Given that mangrove forests are located in the intertidal zone, the period and amplitude of tides may affect the soil greenhouse gas (GHG) fluxes. In this study, soil GHG fluxes and soil characteristics during both spring tide and neap tide days in summer were investigated in a mangrove forest in Jiulong River Estuary, Fujian, to examine the response of greenhouse gas fluxes to tidal conditions and soil physiochemical characteristics. Results showed that the soil fluxes of N₂O, CH₄ and CO₂ in summer ranged from 0.04 μmol/(m²·h) to 3.60 μmol/(m²·h), from −10.59 μmol/(m²·h) to 57.48 µmol/(m²·h), and from 2.32 mmol/(m²·h) to 7.60 mmol/(m²·h), respectively. The CO₂ flux was significantly higher on the neap tide day than spring tide day; while the N₂O flux was affected by the sampling time, and the fluxes during the lowest tide period were higher in the neap tide day than in the spring tide day. However, the CH₄ flux was neither affected by the tidal type nor the sampling time on each day. The total global warming potential of N₂O, CH₄ and CO₂, expressed as their total CO₂-equivalent flux, was higher on the neap tide day than the spring tide day. Both CO₂ and N₂O fluxes were negatively correlated with soil NO₃⁻-N content. The results suggest that CO₂ flux was the main factor causing the differences in the CO₂-equivalent flux of GHGs between the two sampling days.