Floating plants reduced methane fluxes from wetlands by creating a habitat conducive to methane oxidation

Wetlands are one of the important natural sources of atmospheric methane (CH_4),as an important part of wetlands,floating plants can be expected to affect methane release.However,the effects of floating plants on methane release are limited.In this study,methane fluxes,physiochemical properties of the overlying water,methane oxidation potential and rhizospheric bacterial community were investigated in simulated wetlands with floating plants Eichhornia crassipes,Hydrocharis dubia,and Trapa natans.We found that E.crassipes,H.dubia,and T.natans plants could inhibit 84.31%-97.31%,4.98%-88.91%and 43.62%-92.51%of methane fluxes at interface of water-atmosphere compared to Control,respectively.Methane fluxes were negatively related to nutrients concentration in water column but positively related to the aerenchyma proportions of roots,stems,and leaves.At the same biomass,root of E.crassipes (36.44%) had the highest methane oxidation potential,followed by H.dubia (12.99%) and T.natans (11.23%).Forty-five bacterial phyla in total were identified on roots of three plants and 7 bacterial genera (2.10%-3.33%) were known methanotrophs.Type I methanotrophs accounted for 95.07%of total methanotrophs.The pmoA gene abundances ranged from 1.90×10^(16)to 2.30×10^(18)copies/g fresh weight of root biofilms.Abundances of pmoA gene was significantly positively correlated with environmental parameters.Methylotrophy (5.40%) and methanotrophy (3.75%) function were closely related to methane oxidation.This study highlights that floating plant restoration can purify water and promote carbon neutrality partially by reducing methane fluxes through methane oxidation in wetlands.

Distribution and relationship between antimicrobial resistance genes and heavy metals in surface sediments of Taihu Lake,China

Heavy metals, pharmaceuticals, and other wastes released into the environment can significantly influence environmental antibiotic resistance. We investigated the occurrence of 22 antimicrobial resistance genes(ARGs) and 10 heavy metal concentrations, and the relationship between ARGs and heavy metals in surface sediment from seven sites of Lake Taihu. The results showed significant correlations(p < 0.05) between sediment ARG levels,especially for tetracycline and sulfonamides(e.g., tet(A), tet(D), tet(E), tet(O), sul1, sul2 and int-1) and specific heavy metals(Fe, Mn, Cr, Cu, Zn, among others) in the Lake. In the surface sediments, heavy metals showed an interaction with resistance genes, but the strength of interaction was diminished with increasing depth. For most of the heavy metals, the concentration of elements in the top sediments was higher than that in other depths.Tetracycline resistance genes(tet(A), tet(B), tet(D), tet(E) and tet(O), β-lactam resistance genes(SHV, TEM, CTX, OXA and OXY) and sulfonamide resistance genes(sulA, sul1, sul2, sul3 and int-1) were detected. They showed a trend which inferred a statistically significant increase followed by decreases in the relative abundance of these ARGs(normalized to 16 S rRNA genes) with increasing depth. This study revealed that tet(A), tet(O), TEM, OXY, int-1, sul1 and sul3 were widespread in surface sediments with high abundance, indicating that these genes deserve more attention in future work.

Bacterial succession in epiphytic biofilms and deciduous layer sediments during Hydrilla verticillata decay: A field investigation

Submersed macrophytes decay is an important natural process and has important role in mass and energy flow in aquatic ecosystems.However,little is known about the dynamical changes in nutrients release and bacterial community during submersed macrophyte decay in natural environment.In this study,a field observation was conducted in a wetland dominated with Hydrilla verticillata for 36 days.Increase of H2O2 and malondialdehyde(MDA)content and decrease of soluble proteins concentration were detected in leaves during H.verticillata decay.Meanwhile,ammonium-N,soluble microbial products(SMP)and TOC concentration increased in overlying water.According to bacterial 16 S r RNA Illumina sequencing analysis,the Shannon values were lower in epiphytic biofilms than deciduous layer sediments.The relative abundances of Proteobacteria,Cyanobacteria and Actinobacteria were higher in epiphytic biofilms than in deciduous layer sediments(P<0.05).Co-occurrence network analyses showed that a total of 578 and 845 pairs of correlations(|r|>0.6)were identified from 122 and 112 genera in epiphytic biofilms and deciduous layer sediments,respectively.According to co-occurrence patterns,eight hubs were mainly from phyla Proteobacteria,Acidobacteria and Parcubacteria in epiphytic biofilms;while 37 hubs from the 14 phyla(Proteobacteria,Bacteroidetes,Acidobacteria,Chloroflexi,et al.)were detected in deciduous layer sediments.Our results indicate that bacterial community in deciduous layer sediments was more susceptible than in epiphytic biofilms during decay process.These data highlight the role of microbial community in deciduous layer sediments on nutrients removal during H.verticillata decay and will provide useful information for wetland management.