Abstract
Excessive nitrogen (N) input is an important factor influencing aquatic ecosystems and has received increasing public attention in the past decades. It remains unclear how N input affects the denitrifying bacterial communities that play a key role in regulating N cycles in various ecosystems. To test our hypothesis-that the abundance and biodiversity of denitrifying bacterial communities decrease with increasing N-we compared the abundance and composition of denitrifying bacteria having nitrous oxide reductase gene (nosZ I) from sediments (0-20 cm) in five experimental ponds with different nitrogen fertilization treatment (TN10, TN20, TN30, TN40, TN50) using quantitative PCR and pyrosequencing techniques. We found that (1) N addition significantly decreased nosZ I gene abundance, (2) the Invsimpson and Shannon indices (reflecting biodiversity) first increased significantly along with the increasing N loading in TN10-TN40 followed by a decrease in TN50, (3) the beta diversity of the nosZ I denitrifier was clustered into three groups along the TN concentration levels: Cluster I (TN50), Cluster II (TN40), and Cluster III (TN10-TN30), (4) the proportions of Alphaproteobacteria and Betaproteobacteria in the high-N treatment (TN50) were significantly lower than in the lower N treatments (TN10-TN30). (5) The TN concentration was the most important factor driving the alteration of denitrifying bacteria assemblages. Our findings shed new light on the response of denitrification-related bacteria to long-term N loading at pond scale and on the response of denitrifying microorganisms to N pollution.
Highlights
Nitrogen (N) is a key element sustaining life and is one of the most abundant elements on earth [1]
Data on sediment characteristics are provided in Table 1. pH in TN40 and TN50 were significantly lower than in TN20 and TN30
We found that N addition in the ponds had a marked effect on the community and abundance of denitrifying bacteria, as assessed by marker gene analysis of sediment samples collected about 7 years after the initiation of the experimental treatments with contrasting N loadings of the ponds
Summary
Nitrogen (N) is a key element sustaining life and is one of the most abundant elements on earth [1]. Unintentional N enrichment has a variety of negative environmental impacts, including soil acidification [4], reduction of global terrestrial biodiversity [5], increased nutrient runoff to aquatic ecosystems, and eutrophication worldwide [6], and such changes can impact ecosystem services and human well-being [7]. Bacteria-mediated denitrification is potentially an important pathway for N removal by converting nitrate/nitrite into gaseous products (N2, NO, N2O) [8]. N fertilizer has been shown to reduce N2O emission from field crops [14], and N addition increased the denitrification potential in the Broadbalk wheat experiment [15]. The change of N2O-producing bacteria at different nitrogen loadings is unclear
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