Nitrogen Retention in Mesocosm Sediments Received Rural Wastewater Associated with Microbial Community Response to Plant Species

Vegetated drainage ditches (eco-ditches) have drawn much attention in recent years for the ability to remediate diffuse contaminants in rural wastewater through sediment retention, plant uptake and interception, and microbial metabolic activities. However, the effect of plant species on microbial community structure and nitrogen (N) retention in ditch sediment remains poorly understood. In this study, mesocosm plastic drums were planted with eight plant species commonly found in ditches and nurtured with wastewater for 150 days. Sediment total nitrogen (TN) was greatly increased after 150-day nurturing with rural wastewater, from 296.03 mg∙kg−1 (Iris japonica Thunb) to 607.88 mg∙kg−1 (Acorus gramineusO). This study also presents the effect of different plant species on sediment microbial communities, thus providing insight into N removal mechanisms in eco-ditch. Fifty-eight differentially abundant taxa were identified, and sediment microbial community structure for no plant (CK), Acg, Canna indica (Cai), and Typha latifolia L. (Tyl) was primarily linked to sediment NH4+-N and TN. Extremely small proportions of ammonia oxidizing bacteria (AOB) and nitrifying bacteria were detected for all treatments, but large proportions of Crenarchaeota, which comprises the widely existent ammonium oxidized archaea (AOA), were found in CK, Acg and Cai. The abundance of Nitrosotalea from Crenarchaeota presented positive correlations with sediment NH4+-N contents and ammonia oxidation function predicted by Faprotax, indicating Nitrosotalea might be the dominant ammonium-oxidizing microbes in sediment samples. The probable NH4+-N removal pathway in wastewater sediment was through a combined effect of AOA, nitrifying bacteria, and anammox.