Effect of carbon source derived from macrophytes on microbial denitrification in constructed wetlands: Role of plant species

Organic matters derived from macrophytes can serve as carbon source in microbial denitrification. In this study, three macrophyte species, namely of macrophytes, Phragmites australis (PA), Acorus calamus (AC), and Scirpus tabernaemontani (ST), were planted in constructed wetlands. The root exudates were extracted, and their effects on microbial denitrification were investigated. Results showed that root exudate release rates were the highest in AC (17.4 μg·g−1 root dry mass [DM]·h−1), followed by ST (15.9 μg·g−1 root DM·h−1) and PA (10.6 μg·g−1 root DM·h−1). The NO3− transformation efficiency was positively correlated to the amount of root exudation (PA: 9.72%, ST: 33.81%, and AC: 37.88%). However, the contributions of root exudation for bacterial denitrification followed the trend PA (54.76%) > ST (53.19%) > AC (29.19%). The copy numbers of NO3−-reducing bacteria gene in PA, ST, and AC were 1.62 × 109, 2.15 × 109, and 2.18 × 109 copies·g−1 soil, which was positively correlated to the root exudation. [Display omitted] •The rates of root exudates release were different among plant species.•The NO3− transformation was positively related to the amount of root exudation.•The contributions of root exudation for denitrification were irrelevant to the amount.•Root exudation had positive effects on the abundance of denitrification bacteria.