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.
Highlights
Hydrology is the most influential factor regulating the structure and function of lakeshore zones, which can be drastically altered 20 by anthropogenic activities, such as the construction and operation of dams and reservoirs (Mitsch and Gosselink, 2007; Sun et al, 2018)
The results indicate that the distribution of plants under hydrological 15 conditions modified the stoichiometric ratio of sediments, resulting in the variations of N2O emission fluxes and microbial communities in vegetation zones
From the perspective of vegetation distribution caused by long-term hydrological conditions, the root systems and litters of plant species modify the physio-chemical conditions of the soil (Zhang et al, 2010), but they provide discrepant organic matter for the activities of microorganisms (Zhai et al, 2013), thereby affecting the emission of N2O
Summary
Hydrology is the most influential factor regulating the structure and function of lakeshore zones, which can be drastically altered 20 by anthropogenic activities, such as the construction and operation of dams and reservoirs (Mitsch and Gosselink, 2007; Sun et al, 2018). The effect of hydrology is reflected in the stratification of vegetation but it indicates that the short-term alternation of wetting and drying in wetland will affect the withering and fall and growth of plants (Wang et al, 2014; Iwanaga and Yamamoto, 2008) This further alters the content of the physio-chemical conditions in the sediment. From the perspective of vegetation distribution caused by long-term hydrological conditions, the root systems and litters of plant species modify the physio-chemical conditions of the soil (Zhang et al, 2010), but they provide discrepant organic matter for the activities of microorganisms (Zhai et al, 2013), thereby affecting the emission of N2O. Short-term dry and wet alternations strongly affect soil carbon 65 and nitrogen cycles and microbial activities, thereby affecting N2O emissions (Cui and Caldwell, 1997; Manzoni et al, 2014)
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