The physiological response of Arundo donax and characteristics of anodic bacterial community in BE-CW systems: Effects of the applied voltage

Abstract

The performance of bioelectrochemically assisted constructed wetland systems planted with Arundo donax were evaluated at applied voltages of 1, 2, 3 and 5 V. The RGR and Proline (Pro) results implied a positive response at the proper applied voltage. In the 3-V group, the RGR sharply climbed to a maximum over two stages, and the Pro reached a higher level of 256.25 μg/g at the end of the first stage without an additional organic carbon source. This result indicated that A. donax was attempting to adapt the 3-V stress via physiological self-regulation and the growth was nearly unaffected. However, in the 5-V group, the great increase in Pro and withering of the aboveground A. donax showed that the voltage stress had become lethal and the plant was not able to endure it through physiological regulation. In addition, Anodic microbial community compositions accumulating on graphite felts were analyzed via high-throughput sequencing. Results showed that there were two clear clusters at different applied voltages. One cluster was assembled from the anodic region of the 0-V and 1-V groups, and the other was collected from the 2-V and 3-V samples. At the phylum level, Proteobacteria, Firmicutes and Bacteroidetes were the most common phyla among the samples. However, at the genus level, the dominant genera varied with the applied voltage. The relative abundance of Desulfovibrio increased with increased applied voltage. The highest total nitrogen removal rate in the 2-V group was closely related to the high abundance of the Acinetobacter genus. Moreover, Exiguobacterium became dominant only in the 5-V sample, suggesting that this genus strongly depended on the interactive environment of exudes from A. donax and applied voltage.