Effects of inorganic nitrogen addition on CO₂ and N₂O emissions from wetland soil

Carbon (C) and nitrogen (N) are the two most important elements in the terrestrial ecosystems,and they are highly coupled and affect the global environment through biogeochemical processes.Wetland ecosystem is an important terrestrial C sink,and accumulates a large amount of soil organic C.The increase of soil N availability caused by atmospheric N deposition and human activities may seriously affect the C and N cycling processes in wetland ecosystems.However,the effects of different inorganic N forms on wetland soil CO₂ and N₂O emissions are still not clear.In this study,we selected the seasonal flooded wetland with Deyeuxia angustifolia and paddy soils at 0-10 cm and 10-20 cm depths to examine the effects of different ratios of NH₄⁺-N/NO₃^--N addition (1∶0,3∶1,1∶1,1∶3 and 0∶1,i.e.T1,T2,T3,T4 and T5) on CO₂ and N₂O emissions in the Sanjiang Plain.The results showed that CO₂ emissions significantly decreased after different ratios of NH₄⁺-N/NO₃^--N additions.Compared with the control,the CO₂ emissions decreased by 25.6% (T1)~51.0% (T5) and 21.2% (T3)~42.6% (T4) in the 0-10 cm depth soils,and 4.39% (T3)~34.5%(T5) and 20.4%(T1)~33.2% (T4) in the 10-20 cm depth soils,respectively.The CO₂ emission decreased with the increment of NO₃^--N addition.N₂O emissions in different depths of wetland soil had no obvious change after varied NH₄⁺-N/NO₃^--N addition,while significantly increased in the paddy soil (except T5 treatment).The microbial biomass C of wetland and paddy soil showed different characteristics with different inorganic N addition treatments and soil layers at the end of the incubation experiment.Our results indicated that managing inorganic N fertilizers would increase the soil C sequestration and decrease the emissions of N₂O in wetlands,which will help to slow down the global warming process.