08 Sep 2021

08 Sep 2021

Review status: this preprint is currently under review for the journal BG.

Effect of vegetation distribution driven by hydrological fluctuation on sedimental stoichiometry regulating N2O emissions in freshwater wetland

Huazu Liu1,4, Qiu Jin2,5, Ruijie Shi3, Chengxu Lv3, Junxiao Luo1,4, Yan He1,4, Wei Yang1,4, Xiaoguang Xu3, Shenhua Qian1,4, and Wei Li1,4 Huazu Liu et al.
  • 1Key Laboratory of the Three Gorges Reservoir Region’s Eco-Environment, Ministry of Education, Chongqing University, Chongqing 400045, China
  • 2State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing 210029, China
  • 3School of Environment, Nanjing Normal University, Nanjing 210023, China
  • 4Department of Ecological Sciences and Engineering, Chongqing University, Chongqing 400045, China
  • 5College of Agricultural Science and Engineering, Hohai University, Nanjing 210098, China

Abstract. Hydrological conditions drive the distribution of plant communities in wetlands to form vegetation zones where the material cycling varies with plant species. This mediation effect caused by the distribution of vegetation under hydrological conditions will affect the emission of N2O during the nitrogen migration in wetlands. In this study, five vegetation zones in the second largest wetland of China were investigated in situ during high and low water levels to elucidate the effect mediated by vegetation. With the increase in the rate of change of water levels, the zones of the mud flat, nymphoides, phalaris, carex, and reeds were distributed in sequence in the wetland, and the densities of carbon and nitrogen sequestrated by plants also increased. The carbon and nitrogen densities in each zone during low water level was significantly higher than that during high water level, while the organic carbon and the total nitrogen of sediments during high water level was higher. Sediments converted between source and sink for both carbon and nitrogen, during the annual fluctuation in water level. The flux in N2O emissions showed significant differences between the vegetation zones during each water level period. The emission flux decreased with the increasing C : N ratio in sediments, approximating the threshold at 0.23 μg m−2 h−1 when the C : N ratio > 25. The phylum abundance of Firmicutes, Proteobacteria, and Chloroflexi in sediments increased with flooding. The denitrifying nirS and nirK genes and anammox hzsB gene were significantly affected by water level fluctuation, with the maximal variations of these genes occurring in the mud flat and nymphoides zone. The results indicate that the distribution of plants under hydrological conditions modified the stoichiometric ratio of sediments, resulting in the variations of N2O emission fluxes and microbial communities in vegetation zones. Therefore, hydraulic regulation rather than direct planting would be an effective strategy to reduce greenhouse gas emissions in freshwater wetlands.

Huazu Liu et al.

Status: open (until 20 Oct 2021)

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Huazu Liu et al.


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Short summary
Hydrodynamics drive the distribution of plant communities in wetlands to form vegetation zones where the emission of N2O varies with plant species. The N2O emission decreased with the increase in carbon to nitrogen ratio of sediments, approximating a threshold. The distribution of plants under hydrodynamics modified the sedimental chemistry, resulting in the variations of bacteria. Hydraulic regulation rather than direct planting would be an effective strategy to reduce N2O in wetlands.