Response of N2O emissions to elevated water depth regulation: comparison of rhizosphere versus non-rhizosphere of Phragmites australis in a field-scale study
2016
Gu, Xiao-zhi | Chen, Kai-ning | Wang, Zhao-de
Emissions of nitrous oxide (N₂O) from wetland ecosystems are globally significant and have recently received increased attention. However, relatively few direct studies of these emissions in response to water depth-related changes in sediment ecosystems have been conducted, despite the likely role they play as hotspots of N₂O production. We investigated depth-related differential responses of the dissolved inorganic nitrogen distribution in Phragmites australis (Cav.) Trin. ex Steud. rhizosphere versus non-rhizosphere sediments to determine if they accelerated N₂O emissions and the release of inorganic nitrogen. Changes in static water depth and P. australis growth both had the potential to disrupt the distribution of porewater dissolved NH₄⁺, NO₃⁻, and NO₂⁻ in profiles, and NO₃⁻ had strong surface aggregation tendency and decreased significantly with depth. Conversely, the highest NO₂⁻ contents were observed in deep water and the lowest in shallow water in the P. australis rhizosphere. When compared with NO₃⁻, NH₄⁺, and NO₂⁻, fluxes from the rhizosphere were more sensitive to the effects of water depth, and both fluxes increased significantly at a depth of more than 1 m. Similarly, N₂O emissions were obviously accelerated with increasing depth, although those from the rhizosphere were more readily controlled by P. australis. Pearson’s correlation analysis showed that water depth was significantly related to N₂O emission and NO₂⁻ fluxes, and N₂O emissions were also strongly dependent on NO₂⁻ fluxes (r = 0.491, p < 0.05). The results presented herein provide new insights into inorganic nitrogen biogeochemical cycles in freshwater sediment ecosystems.
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