Decaying cyanobacteria decrease N2O emissions related to diversity of intestinal denitrifiers of Chironomus plumosus

摘要

Nitrous oxide (N 2 O) emission of fresh invertebrates has too long been neglected in eutrophic lakes, although the sediments these animals inhabit are presumably hot spots of N 2 O emission. Thus, the experiment in this research was designed to gain insight into the influence of cyanobacteria l degradation on the N 2 O emission by fresh water invertebrates (Chironomus plumosus). The presence of decaying cyanobacteria in Lake Taihu decreased the N 2 O emission rate of Chironomus plumosus larvae from the larvae body by almost 400% for the larvae as a whole. The N 2 O emission rate decreased by 350% based on readings from studies of their gut, which was mostly due to stimulation of intestinal complete denitrification. The quantitative PCR results showed that intestinal gene abundance of nirK , nosZ (encoding the copper nitrite reductase and N 2 O reductase, respectively) were significantly increased with the presence of decaying cyanobacteria. In contrast nirS (encoding the cytochrome cd 1 heme nitrite reductase) and the total bacteria decreased. In the gut of Chironomus plumosus , the diversity and richness of nosZ and nirK were lower with the cyanobacteria. Phylogenetic analysis of the intestinal function genes ( nosZ and nirK ) showed that the nosZ - and nirK -type denitrifying bacterial sequences were related to different phylotypes. Hence, additional cyanobacteria increased the abundance, but decreased the richness and diversity of intestinal nitrate-reducing bacteria, probably by providing more carbon source in the gut. The data obtained in this study elucidates that the decaying cyanobacteria decreased the emissions of N 2 O by the aquatic invertebrates in freshwater sediment and could serve as a valuable resource for nitrogen removal affecting greenhouse gas emissions.