Soil nitrogen dynamics following short-term revegetation in the water level fluctuation zone of the Three Gorges Reservoir, China

Background/Question/Methods

Revegetation and flooding plays an important role in regulating nitrogen (N) dynamics in riparian ecosystems. With the implement of the Three Gorges project, the water-level-fluctuation zone formed along the two sides of Three Gorges Reservoir, which resulted in various ecological problems. To restore and protect the riparian ecosystem, the revegetation with three types (herbs, shrubs and trees) project has been carried out for recent years. The objective of this study was to better understand how soil nitrogen (N) changes following short-term revegetation and environmental changes (i.e. flooding) in a riparian ecosystem. We conducted a field experiment to study the variations on soil N dynamics following short-term revegetation and flooding in three plant communities in the region of Zhongxian, Revegetation Research Station in the water-level-fluctuation zone of the Three Gorges Reservoir during the period from 2008 to 2009. We collected soil samples before revegetation at March 2008 and after revegetation at September 2008 June 2009 and September 2009. We examined net mineralization potential rate (NMPR), net nitrification potential rate (NNPR) and denitrification potential rate (DPR) by using the laboratory incubation and also analyzed the soil chemical and physical characteristics.

Results/Conclusions

Our results showed that there were significantly decreases in inorganic N (NH₄⁺ -N plus NO₃^- -N) concentrations and increases in NMPR and NNPR following the short-term revegetation, whereas significantly increased DPR was only found at the beginning of the revegetation. Vegetation types affected inorganic N, NMPR and NNPR and DPR by changing soil organic carbon (SOC) and C:N ratios. Higher SOC in shrub soils led to higher inorganic N, NMPR and NNPR compared to herb and tree soils, whereas lower C:N ratios resulted in lower DPR in tree soils. Significantly increased NO₃^- -N and NNPR, and decreased NH₄⁺ -N, C:N ratios and DPR after flooding were possibly due to lower soil bulk density and frequent material exchanges during the submergence period. We implicate that revegetation is important in reducing soil inorganic N and potentially improve water quality in riparian ecosystems. Vegetation types have different affects on soil N dynamics due to different C input.