Effect of Eichhornia crassipes on production of N2 by denitrification in eutrophic water

The floating aquatic macrophyte may stimulate the gaseous nitrogen production via denitrificaiton in eutrophic water. In order to justify this hypothesis, an improved floating-chamber method was deployed to directly measure the productions of N2 and N2O from the eutrophic water with or without growth of Eichhornia crassipes. The abundance of denitrifiers attached to E. crassipes root surface and in the water was measured. The interactions between E. crassipes and sediment on mediating N2 production in eutrophic water were also analyzed. Within the experimental duration of 12 days, the values of N-15 at.% excess of N2-N were significantly (p < 0.05) higher with the growth of E. crassipes than that without. Regardless of added sediment or not, the total removal amounts of N2 and N2O from the water were significantly (p < 0.05) higher in the planted treatments (4.9-6.7 g N m−3 without added sediment; 9.8-12.4 g N m−3 with added sediment) than non-planted treatments (2.9-3.4 g N m−3 without added sediment; 3.6-6.0 g N m−3 with added sediment). The total removal rates of N2 and N2O from the water were significantly (p < 0.05) higher in the planted treatments (63-71% without added sediment; 161-179% with added sediment) than non-planted treatments (41-44% without added sediment; 79-81% with added sediment). Regardless of plant presence or absence, the total removal amounts and rates of N2 and N2O from the water were significantly (p < 0.05) higher in the treatments with added sediment than without. The positive interactions (p < 0.01) between E. crassipes and sediment on promoting N2 production from the water were observed. The presence of E. crassipes significantly promoted the abundances of nosZ (p < 0.05), nirK (p < 0.01) and nirS gene (p < 0.01) in the water. The results indicated that cultivation of E. crassipes could have a stimulating effect on the gaseous production of N2 by denitrification in the eutrophic water.