Lower Compositional Variation and Higher Network Complexity of Rhizosphere Bacterial Community in Constructed Wetland Compared to Natural Wetland.

Macrophyte rhizosphere microbes, as crucial components of the wetland ecosystem, play an important role in maintaining the function and stability of natural and constructed wetlands. Distinct environmental conditions and management practices between natural and constructed wetlands would affect macrophytes rhizosphere microbial communities and their associated functions. Nevertheless, the understanding of the diversity, composition, and co-occurrence patterns of the rhizosphere bacterial communities in natural and constructed wetlands remains unclear. Here, we used 16S rRNA gene high-throughput sequencing to characterize the bacterial community of the rhizosphere and bulk sediments of macrophyte Phragmites australis in representative natural and constructed wetlands. We observed higher alpha diversity of the bacterial community in the constructed wetland than that of the natural wetland. Additionally, the similarity of bacterial community composition between rhizosphere and bulk sediments in the constructed wetland was increased compared to that of the natural wetland. We also found that plants recruit specific taxa with adaptive functions in the rhizosphere of different wetland types. Rhizosphere samples of the natural wetland significantly enriched the functional bacterial groups that mainly related to nutrient cycling and plant-growth-promoting, while those of the constructed wetland-enriched bacterial taxa with potentials for biodegradation. Co-occurrence network analysis showed that the interactions among rhizosphere bacterial taxa in the constructed wetland were more complex than those of the natural wetland. This study broadens our understanding of the distinct selection processes of the macrophytes rhizosphere-associated microbes and the co-occurrence network patterns in different wetland types. Furthermore, our findings emphasize the importance of plant-microbe interactions in wetlands and further suggest P. australis rhizosphere enriched diverse functional bacteria that might enhance the wetland performance through biodegradation, nutrient cycling, and supporting plant growth.

Evaluation of the carbon accumulation capability and carbon storage of different types of wetlands in the Nanhui tidal flat of the Yangtze River estuary.

Wetlands are carbon pools for terrestrial ecosystems and play an important role in the global carbon cycle. The Nanhui tidal flat is located at the Yangtze River estuary and has been disturbed by various human activities. However, the effect of human activities on the carbon accumulation capability and carbon storage of wetlands in the Nanhui tidal flat is poorly understood. In this study, the annual carbon accumulation capability and carbon storage of three types of Spartina alterniflora Loisel. wetlands in the Nanhui tidal flat, which were defined as a natural wetland, silt-promoting wetland, and artificial restored wetland, were evaluated by analyzing the plant carbon fixation capability, soil carbon emissions, and soil organic carbon (SOC) density. The results showed that the three wetlands all had a carbon sink effect and the natural wetland, artificial restored wetland, and silt-promoting wetland annually accumulated 7.94, 7.14, and 6.33 kg m-2 CO2, respectively. The existing SOC density in the subsurface soil (0-40 cm) in the natural wetland, silt-promoting wetland, and artificial restored wetland was 23.26, 17.95, and 12.21 kg m-2 CO2, respectively. The natural wetland, with no human disturbance, had a longer duration of waterlogging and greater tidal nutrition inputs than the other wetlands, resulting in a higher plant biomass and lower soil respiration (SR). It therefore had the strongest carbon accumulation capability and highest SOC storage.

Performance of CH4MODwetland for the case study of different regions of natural Chinese wetland.

Reliable national estimates of CH4 emissions from natural wetlands depend on model validation based on site observations. We therefore evaluated the performance of the CH4MODwetland model in simulating CH4 emissions from 11 representative wetland sites in five regions of China. Model performance analysis showed that this method effectively simulates differences in the CH4 fluxes between different sites and regions. The model efficiency for estimating the daily CH4 fluxes in the northeastern China (NE), Inner Mongolia and northwestern China (NW), the North China plain and the Middle-Lower Yangtze Plain (E) and the Qinghai Tibetan Plateau (SW) was 0.51, 0.20, 0.52 and 0.65, respectively. The efficiency for estimating the annual mean CH4 fluxes in southern China (S) was 0.99. Systematic negative deviation between the simulated and observed CH4 emissions existed in all regions, especially in the NW region, which had a mean deviation (RMD) value of -36.7%. On the national scale, the root mean square error (RMSE), the RMD, the model efficiency (EF) between the simulated and observed seasonal values were 28.7%, -7.8% and 0.93, respectively. The CH4 emissions showed the highest sensitivity to air temperature in the NE and SW regions, and to water table depth in the E region. Based on the sensitivity analysis, future climate warming and wetting are likely to increase the wetland CH4 emissions at different levels in all regions of China.

Natural wetlands contribution on phosphorus removal in small northern communities in Canada.

This study focuses on understanding the role of passive wastewater treatment (wastewater lagoon plus wetland) in reducing the phosphorus discharge levels in a northern small community in Manitoba, Canada. The facultative lagoon system of that small community treats domestic wastewater and seasonally discharges effluent into a wetland that connects to Lake Manitoba. This research assesses phosphorus removal efficiency through the natural wetland during the vegetation growing season. The average total phosphorus (TP) concentration reduction for the observed treatment area of 1.3 ha was more than 70%, achieving the desired TP discharge concentration below 1 mg/L. Data analysis showed that the main accumulation of TP occurred at the 21-40 cm soil depth, which indicates the potential of natural wetland treatment applications under cold continental climate conditions as an effluent polishing step to satisfy regulatory requirements for phosphorus reduction.

Comparative insight of pesticide transformations between river and wetland systems.

The widespread use of pesticides threatens the environment and ecosystems. Despite the positive effects of plant protection products, pesticides also have unexpected negative effects on nontarget organisms. The microbial biodegradation of pesticides is one of the major pathways for reducing their risks at aquatic ecosystems. The objective of this study was to compare the biodegradability of pesticides in simulated wetland and river systems. Parallel experiments were conducted with 17 pesticides based on the OECD 309 guidelines. A comprehensive analytical method, such as target screening combined with suspect and non-target screening, was performed to evaluate the biodegradation via identification of transformation products (TPs) using LC-HRMS. As evidence of biodegradation, we identified 97 TPs for 15 pesticides. Metolachlor and dimethenamid had 23 and 16 TPs, respectively, including Phase II glutathione conjugates. The analysis of 16S rRNA sequences for microbials characterized operational taxonomic units. Rheinheimera and Flavobacterium, which have the potential for glutathione S-transferase, were dominant in wetland systems. Estimation of toxicity, biodegradability, and hydrophobicity using QSAR prediction indicated lower environmental risks of detected TPs. We conclude that the wetland system is more favorable for pesticide degradation and risk mitigation mainly attributed to the abundance and variety of the microbial communities.

Relevance of the microbial community to Sb and As biogeochemical cycling in natural wetlands.

Mining activities lead to elevated levels of antimony (Sb) and arsenic (As) in river systems, having adverse effects on the aquatic environment and human health. Microbes inhabiting river sediment can mediate the transformation of Sb and As, thus changing the toxicity and mobility of Sb and As. Compared to river sediments, natural wetlands could introduce distinct geochemical conditions, leading to the formation of different sedimentary microbial compositions between river sediments and wetland sediments. However, whether such changes in microbial composition could influence the microbially mediated geochemical behavior of Sb or As remains poorly understood. In this study, we collected samples from a river contaminated by Sb tailings and a downstream natural wetland to study the influence of microorganisms on the geochemical behavior of Sb and As after the Sb/As-contaminated river entered the natural wetland. We found that the microbial compositions in the natural wetland soil differed from those in the river sediment. The Sb/As contaminant components (Sb(III), As(III), As(V), Asexe) and nutrients (TC) were important determinants of the difference in the compositions of the microbial communities in the two environments. Taxonomic groups were differentially enriched between the river sediment and wetland soil. For example, the taxonomic groups Xanthomonadales, Clostridiales and Desulfuromonadales were important in the wetland and were likely to involve in Sb/As reduction, sulfate reduction and Fe(III) reduction, whereas Burkholderiales, Desulfobacterales, Hydrogenophilales and Rhodocyclales were important taxonomic groups in the river sediments and were reported to involve in Sb/As oxidation and sulfide oxidation. Our results suggest that microorganisms in both river sediments and natural wetlands can affect the geochemical behavior of Sb/As, but the mechanisms of action are different.

Methanotrophs Contribute to Nitrogen Fixation in Emergent Macrophytes.

Root-associated aerobic methanotroph plays an important role in reducing methane emissions from wetlands. In this study, we examined the activity of methane-dependent nitrogen fixation and active nitrogen-fixing bacterial communities on the roots of Typha angustifolia and Scirpus triqueter using a 15N-N2 feeding experiment and a cDNA-based clone library sequence of the nifH gene, respectively. A 15N-N2 feeding experiment showed that the N2 fixation rate of S. triqueter (1.74 µmol h-1 g-1 dry weight) was significantly higther than that of T. angustifolia (0.48 µmol h-1 g-1 dry weight). The presence of CH4 significantly increased the incorporation of 15N-labeled N2 into the roots of both plants, and the rate of CH4-dependent N2 fixation of S. triqueter (5.6 µmol h-1 g-1 dry weight) was fivefold higher than that of T. angustifolia (0.94 µmol h-1 g-1 dry weight). The active root-associated diazotrophic communities differed between the plant species. Diazotrophic Methylosinus of the Methylocystaceae was dominant in S. triqueter, while Rhizobium of the Rhizobiaceae was dominant in T. angustifolia. However, there were no significant differences in the copy numbers of nifH between plant species. These results suggest that N2 fixation was enhanced by the oxidation of CH4 in the roots of macrophytes grown in natural wetlands and that root-associated Methylocystacea, including Methylosinus, contribute to CH4 oxidation-dependent N2 fixation.

Function of restored wetlands for waterbird conservation in the Yellow Sea coast.

To reduce the harm to wildlife caused by habitat loss and degradation, significant resources have been invested in habitat restoration worldwide. However, whether restored habitats can support wildlife communities similar to those natural ones remains unclear. Providing habitat for waterbirds, which are dependent on wetland for their survival, is a major target in many wetland restoration practices. Here we conducted a year-round waterbird survey at Chongming Dongtan, a national nature reserve established for waterbird conservation in the south Yellow Sea, in order to compare the characteristics of waterbird communities in four wetland types: restored wetlands, natural tidal wetlands, and two artificial wetlands (fish ponds and farmlands). We determined whether waterbird diversity and species composition differed among the wetland types. The results indicated that waterbird diversity, in terms of species richness, individual density, Shannon-Wiener diversity, functional diversity, and phylogenetic diversity, was generally similar in the restored and natural wetlands and was higher in the restored and natural wetlands than in fish ponds or farmlands. Most threatened species and exclusive species occurred in both natural and restored wetlands, but the overall species composition significantly differed between natural and restored wetlands. Non-metric multidimensional scaling analysis also indicated that waterbird community significantly differed among the wetland types. The results suggest that restored wetlands support substantial waterbird diversity but cannot replace natural wetlands because they lack the period tides that many tideland specialists (shorebirds) depend on. This study highlights the importance of protecting natural wetlands for waterbird conservation. We propose that both the diversity and species composition of wildlife communities should be considered in evaluating the effectiveness of habitat restoration for wildlife.

Magnitudes and environmental drivers of greenhouse gas emissions from natural wetlands in China based on unbiased data.

Whether natural wetlands serve as the source or sink of greenhouse gases (GHGs) remains uncertain. Wetlands in China are diverse in type and abundant in quantity and differ greatly in spatial distribution, environmental conditions, and GHG fluxes. However, few studies focused on the differences in GHG emissions from different types of natural wetlands. Here, we adopted strict data collection criteria to create comprehensive and detailed datasets of fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from the marsh, coastal, lake, and river wetlands in China, and relevant environmental variables. Our study synthesized 265 field observations on GHGs that lasted at least one year (covering both the growing season and non-growing season) from 109 studies, among which CO2 measurements using the opaque chamber method were not included for eliminating the influence of absence of photosynthesis on net CO2 accounting. We found that CH4 contributed the largest warming effect among the three types of GHGs, and coastal and river wetlands respectively acted as the mitigators and motivators of global warming among the four types of wetlands. Correlation and regression analyses suggested that geographic location, soil moisture and organic carbon, and contents of nitrogen, phosphorus, and dissolved oxygen jointly drove wetland GHG fluxes. The comprehensive global warming potential of Chinese natural wetlands was estimated as 427 Tg CO2-equivalents year-1, which might result from increased wetland drainage, reclamation, and external nutrient inputs. This study highlights the incorporation of the full year-round GHG monitoring data without using opaque chambers to measure CO2 flux when extrapolating net GHG emissions and gives implications for natural wetland management and global warming mitigation strategies.

Fungal Clusters and Their Uniqueness in Geographically Segregated Wetlands: A Step Forward to Marsh Conservation for a Wealth of Future Fungal Resources.

Here, we investigated fungal microbiota in the understory root layer of representative well-conserved geographically segregated natural wetlands in the Korean Peninsula. We obtained 574,143 quality fungal sequences in total from soil samples in three wetlands, which were classified into 563 operational taxonomic units (OTU), 5 phyla, 84 genera. Soil texture, total nitrogen, organic carbon, pH, and electrical conductivity of soil were variable between geographical sites. We found significant differences in fungal phyla distribution and ratio, as well as genera variation and richness between the wetlands. Diversity was greater in the Jangdo islands wetland than in the other sites (Chao richness/Shannon/Simpson's for wetland of the Jangdo islands: 283/6.45/0.97 > wetland of the Mt. Gariwang primeval forest: 169/1.17/0.22 > wetland of the Hanbando geology: 145/4.85/0.91), and this variance corresponded to the confirmed number of fungal genera or OTUs (wetlands of Jangdo islands: 42/283 > of Mt. Gariwang primeval forest: 32/169 > of the Hanbando geology: 25/145). To assess the uniqueness of the understory root layer fungus taxa, we analyzed fungal genera distribution. We found that the percentage of fungal genera common to two or three wetland sites was relatively low at 32.3%, while fungal genera unique to each wetland site was 67.7% of the total number of identified fungal species. The Jangdo island wetland had higher fungal diversity than did the other sites and showed the highest level of uniqueness among fungal genera (Is. Jangdo wetland: 34.5% > wetland of Mt. Gariwang primeval forest: 28.6% > wetland of the Hanbando geology: 16.7%).

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To understand the potential role of soil seed bank in natural vegetation restoration of Populus deltoides cutting slash in Lake Dongting, the structure and diversity of soil seed bank and its relationship with vegetation and soil parameters were observed and analyzed on the lake beach in the first two years after P. deltoides cutting, with P. deltoides lake beach as control (CK). A total of 65 plant species germinated in soil seed bank, belonging to 59 genera and 23 families. The density of soil seed bank and number of species ranked as 1-year cutting slash (11810 seeds·m-2, 49 species)> 2-year cutting slash (9686 seeds·m-2, 44 species)> CK (6735 seeds·m-2, 29 species). Compared with CK, species diversity of the perennial mesophytes and hygrophytes in the soil seed bank and aboveground vegetation of cutting slash, as well as the similarity coefficient between soil seed bank and aboveground vegetation, increased. Soil water content and nutrient content increased, while the pH decreased. Soil water content and organic matter were closely related to the distribution of hydrophytes such as Polygonum hydropiper, while total potassium and phosphorus contents had a greater influence on the distribution of perennial species such as Phalaris arundinacea. In summary, during the natural restoration of P. deltoides cutting slash in Lake Dongting, with the changes of soil physicochemical properties, species richness and density of soil seed bank increased significantly, and the diversity of aboveground vegetation species therefore increased. Soil seed bank is an important propagule source for the restoration of wetland vegetation in cutting slash.

Identification of transformation products to characterize the ability of a natural wetland to degrade synthetic organic pollutants.

Natural wetlands have been recognized as a natural reactor for degradation and elimination of environmental pollutants. The Upo Wetland, the largest inland wetland in Korea, is mainly surrounded by agricultural lands and it is susceptible to contamination from excess nutrient loads and synthetic organic contaminants (SOCs) (e.g., pesticides). The aim of this study was to identify major SOCs in the wetland and evaluate their degradation. We used high resolution mass spectrometry (HRMS) with a two-step analysis approach (i.e., 1st analysis for target measurement along with suspect and non-target screening (SNTS) and 2nd analysis for complimentary suspect screening) to identify and quantify the transformation products (TPs) of the identified parent SOCs. Quantitative analysis of 30 targets, mainly including pesticides, showed that fungicides were the major SOCs detected in the wetland, accounting for about 50% of the composition ratio of the total SOCs quantified. Orysastrobin occurred at the highest mean concentration (>700 ng/L), followed by two other fungicides, carbendazim and tricyclazole. The first analysis (SNTS) tentatively identified 39 TPs (30 by suspect, 9 by non-target screening) of 14 parent pesticides. Additionally, the second analysis (complimentary suspect screening) identified 9 more TPs. Among the 48 total TPs identified, 7 were confirmed with reference standards. The identification of the remaining TPs had a high confidence level (e.g., level 2 or 3). Regarding transport though the wetland, most TPs showed greater peak area ratios (i.e., the relative portion of chromatographic area of the TPs to the parent compound) at the outlet point of the wetland compared to the inlet point. The risk quotient, which was calculated using the concentrations of parent compounds, decreased toward the outlet, demonstrating the degradation capacity of the wetland. The estimates for biodegradability, hydrophobicity, and toxicity by an in-silico quantitative structure-activity relationship (QSAR) model indicated a lower half-life, lower logDOW, and greater effect concentration for most TPs compared to the parent compounds. Based on these results, we conclude that natural wetlands play a role as an eco-friendly reactor for degrading SOCs to form numerous TPs that are lower risk than the parent compounds.