| Excessive nitrogen (N) and phosphorus (P) loading in freshwater lakes can cause eutrophication resulting in algal blooms, reduced oxygen concentration, and an alteration in ecosystem structure and function. During the N transportation in lake ecosystems, nitrification and denitrification processes mediated by microorganisms may decrease the N loading by returning nitrogen into the atmosphere to relieve the eutrophication stress for sustaining the nutrient balance. Zoobenthos living at the bottom of aquatic ecosystems are important mediators between nutrients in the water column and microbes in the benthos. The presence of zoobenthos stimulates microbial nutrient dynamics, which potentially affect the transformation of nitrogen in aquatic ecosystems. Therefore, it need to investigate the influence of zoobenthos on microbial community structure and function involved in N-cycling in eutrophic lake. The data obtained in this study could be useful to better understand the lake ecosystem and explore the way to remove N from eutrophic lake.Real-time PCR (qPCR) combined with microbial molecular ecology techniques (terminal restriction fragment length polymorphism, clone library, high throughput screening) were employed to investigate the spatial distribution of ammonia-oxidizing archaea and bacteria across eight freshwater lakes in sediments from Jiangsu of China, and influence of zoobenthos on the abundance, diversity, and community structure of the nitrifier and denitrifier, consequently, the delivery of ecosystem functioning in eutrophic lake. The data obtained in this study would be useful to elucidate the role of benthic macrofauna in the nitrogen cycle of eutrophic lake. The main conclusions are as follows:The results showed that AOA and AOB were ubiquitous in all sediments and archaeal amoA far outnumbered bacterial amoA in most sediments with lower organic matters. The archaeal amoA gene copy numbers ranged from 6.6×104 per gram of dry sediment to 3.9×107 per gram of dry sediment, whereas the bacterial amoA gene copy numbers ranged from 2.6×105 per gram of dry sediment to 2.4×107 per gram of dry sediment. The abundance of AOA and AOB did not vary with the freshwater ecological type (macrophyte dominated region and algae dominated region). Based on terminal restriction fragment length polymorphism of amoA gene, organic matters in pore water rather than other factors could affect the AOA community structure in sediments, while the AOB were not significant different in the freshwater sediments. Phylogenetic analysis showed that all archaeal amoA sequences fell within either Crenarchaeotal Group (CG) I.1b or CGI.1a subgroup, and all AOB clustered with genus Nitrosospira or Nitrosomonas. The sequences affiliated with the CG I.1b (S) were all derived from sediment in the eutrophic zones, whereas in the CG I.1a (M), the sequences came from both zones. Nitrosospira-like sequences were ubiquitous and dominated at all sites, whereas most Nitrosomonas sequences appeared in eutrophic zones. In eutrophic lake sediments the distribution of AOA and AOB has a significant spatial heterogeneity and organic substances have an important role in ammonia oxidizers community structure.The zoobenthos could stimulate the nitrification in sediments and water column. The abundance and diversity of bacterial and ammonia oxidizers in sediments would increase with the presence of zoobenthos, while the bacterial and AOB community structure also changed by the zoobenthos, increased the abundance of Nitrosomonas europaea and decreased the abundance of Nitrosomonas communis. The influence of Corbiculafluminea on the bacterial and ammonia oxidizers community structure were stronger than the influence of Chironomus plumosus. These data suggest that the C. plumosus and C. fluminea could affect the bacterial and ammonia oxidizers community composition and diversity in sediment, resulting in stimulating the nitrification in sediments.The presence of cyanobacteria and zoobenthos would release NH4+ to the sediment, decrease the concentration of nitate and nitrite leading to increase the nitrification and denitrification. The influence of Corbicula fluminea on the N transformation was stronger than the influence of Chironomus plumosus. The quantitative PCR results showed that the abundance of ammonia oxidizers and denitrifiers were significantly increased with the presence of cyanobacteria and zoobenthos.The abundance of AOA and nirK gene were higher in sediments with cyanobacteria and C. plumosus; whereas the abundance of AOB and nirS gene were higher in sediments with cyanobacteria and C. fluminea. High throughput sequencing for amoA gene suggested all archaeal amoA sequences fell within either the Crenarchaeotal Group (CG) I.1b or the CG I.la subgroup, and all AOB clustered with genus Nitrosomonas. The community structure and diversity of AOB were significant changed by cyanobacteria and zoobenthos. This suggested that the presence of cyanobacteria and zoobenthos could change the community structure and function of ammonia oxidizers, and promote the nitrification and denitrification.In the gut of C. plumosus larvae there was absence of ammonia oxidition, having the stronger denitrification, lead to N2O emission efflux by the living C. plumosus up to 38.50 pmol ind"1 within two hours. The presence of cyanobacteria decreased the N2O emission rate of Chironomus plumosus larvae from the larvae body by almost 40% for the larvae as a whole. The N2O emission rate decreased by 35% based on readings from studies of their gut, accounted for 77% of total N2O emission from the living animal, indicating that the gut was the major site for N2O emission. The abundance and diversity of bacterial in gut would decrease with the presence of cyanobacteria, while the bacterial community structure also changed by the cyanobacteria,the abundance of P-Proteobacteria in gut with increased up to 40.6%, whereas δ- Proteobacteria decreased up to 4.1%. The quantitative PCR results showed that there was absence of ammonia oxidizers in gut, whlie intestinal gene abundance of nirK, nosZ were respectively increased from 1.1×103 copies·ng-1 DNA and 7.9×103 copies·ng-1 DNA to 2.9×103 copies·ng-1 DNA and 2.8×104 copies·ng-1 DNA with the presence of decaying cyanobacteria. In the gut of C. plumosus, although the diversity and richness of nosZ and nirK were lower with the cyanobacteria, the abundance of denitrifiers increased. Phylogenetic analysis of the intestinal function genes (nosZ and nirK) showed that the unique nosZ type denitrifying bacterial sequences were related to different phylotypes, increased from 3 to 8. Hence, additional cyanobacteria increased the abundance of intestinal nitrate-reducing bacteria, but decreased their richness and diversity, probably by providing more carbon source in the gut, resulting in enhanced growth and activity of microorganisms capable of complete denitrification. |
PDF Full Text Request