Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma Identification of the alteration of riparian wetland on soil properties, enzyme activities and microbial communities following extreme flooding Yang Ou a , Alain N. Rousseau b , Lixia Wang a, ⁎ , Baixing Yan a , Thiago Gumiere b , Hui Zhu a a Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, P.R. China b Centre Eau Terre Environnement, Institut National de la Recherche Scientifique (INRS-ETE), 490 rue de la Couronne, Québec City, Qc G1K 9A9, Canada ARTICLEINFO Handling Editor: Junhong Bai Keywords: Riparian wetland Flooding Soil properties Microbial community structure Soil enzyme activity ABSTRACT In China, most riparian wetlands have undergone degradation and shrinkage, due to severe droughts or low hydrological connectivity. There are considerable studies focusing on the impact of water level on wetland vegetation; however, changes in the soil components, such as the microbial community, of wetlands following flooding remains unclear. Here, we verified the effects of an extreme flooding event on the soil physicochemical conditions, enzyme activities and soil microbial composition. Overall, we observed that the flooding event impacted the soil properties and modified the enzyme activities. Also, the flooding affected more the biomass than the composition of the soil microbial community. We observed that after the flooding event, manganese (Mn) replaced total nitrogen (TN) as one of the major governing factors of soil enzyme activities. Soil organic carbon (SOC), and pH were also correlated with soil enzyme activities before and after the flooding event. Soil conductivity (EC), C/N ratio, and iron (Fe) contents had a large influence on microbial communities. Nevertheless, the soil C/N ratio was the dominant governing factor of the microbial structure. Therefore, edaphic factors were remarkably related to microbial organisms as flooding was deemed a key driving factor to the linkage between them. The antecedent long-term drought provoked by human disturbance, and subsequent flooding (i.e., re-inundating) may thus damage the soil dynamics of riparian wetlands, and hence, altering the carbon storage capacity. The results of this study suggest that rehabilitating hydrological connectivity and promoting primary succession of vegetation could become effective practices for improving the soil ecosystem of riparian wetlands. 1. Introduction The riparian wetland can be viewed as an ecotone between river and terrestrial ecosystems, playing an important role in water storage and purification as well as carbon sequestration (Bernal and Mitsch, 2008; Fossey et al., 2016; Huetal.,2014). In general, flooding has been considered as a key element for development and maintenance of ri- parian systems (Baldwin and Mitchell, 2000; Galat et al., 1998; Unger et al., 2009). It contributes to transport of sediments, nutrients, and biomass from rivers and uplands to riparian wetlands (Thoms, 2003), providing ecological services such as sinks or sources of carbon, nu- trients, biomass and metals, and new habitats for endemic wetland species (Song, 2005). Riparian wetlands are constantly affected by economic develop- ment, located at the ecotone between natural and human disturbances (Barbier et al., 2011; Wu et al., 2013). For example, a flood from an agricultural watershed usually carries a large amount of diffuse pollutants, including nutrients and suspended solids, into riparian wetlands (Riis et al., 2014). In China, most riparian wetlands have undergone degradation and shrinkage, due to severe droughts or low hydrological connectivity due to agricultural land reclamation projects (Huang et al., 2010). The Chinese government has attempted to recover and improve wetland ecosystems using flooding with the development of the Interconnected River System Network project (IRSN). The project aims to rebuild the hydrological connectivity between rivers, lakes, and wetlands of a watershed (Zhao et al., 2017). Flood water replenishment projects of riparian wetlands in China have focused on the natural recovery of native plant communities by the succession of vegetation. However, at the initial stages of succes- sion, plants alone cannot ensure stabilization of restored wetland eco- systems (Nilsson et al., 2010). It has been observed that soil activities and microbes play important roles in the biogeochemical processes in wetlands (Wu et al., 2015). Soil enzymes are the direct agents for the formation and decomposition of soil organic matter (Aon and Colaneri, https://doi.org/10.1016/j.geoderma.2018.10.032 Received 5 March 2018; Received in revised form 17 October 2018; Accepted 19 October 2018 ⁎ Corresponding author. E-mail address: lxwang@iga.ac.cn (L. Wang). Geoderma 337 (2019) 825–833 0016-7061/ © 2018 Elsevier B.V. All rights reserved. T