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Coastal wetland soil organic carbon (CW-SOC) is crucial for both “blue carbon” and carbon sequestration. It is of great significance to understand the content of soil organic carbon (SOC) in soil resource management. A total of 133 soil samples were evaluated using an indoor spectral curve and were categorized into silty soil and sandy soil. The prediction model of CW-SOC was established using optimized support vector machine regression (OSVR) and optimized random forest regression (ORFR). The Leave-One-Out Cross-Validation (LOO-CV) method was used to verify the model, and the performance of the two prediction models, as well as the models’ stability and uncertainty, was examined. The results show that (1) The SOC content of different coastal wetlands is significantly different, and the SOC content of silty soils is about 1.8 times that of sandy soils. Moreover, the characteristic wavelengths associated with SOC in silty soils are mainly concentrated in the spectral range of 500–1000 nm and 1900–2400 nm, while the spectral range of sandy soils is concentrated in the spectral range of 600–1400 nm and 1700–2400 nm. (2) The organic carbon prediction model of silty soil based on the OSVR method under the first-order differential of reflectance (R′) is the best, with the Adjusted-R2 value as high as 0.78, the RPD value is much greater than 2.0 and 5.07, and the RMSE value as low as 0.07. (3) The performance of the OSVR model is about 15~30% higher than that of the support vector machine regression (SVR) model, and the performance of the ORFR model is about 3~5% higher than that of the random forest regression (RFR) model. OSVR and ORFR are better methods of accurately predicting the CW-SOC content and provide data support for the carbon cycle, soil conservation, plant growth, and environmental protection of coastal wetlands.

The dense vegetation in the wetland could effectively retain microplastic particles, and the distribution of microplastics varied significantly under different planting densities. In addition, microplastics in the soil environment can affect soil properties to a certain extent, which in turn can affect soil functions and biodiversity. In this study, we investigated the distribution of soil microplastics in a mangrove restoration wetland under different planting densities and their effects on wetland soil properties. The results indicated that the average abundance of soil microplastics was 2177.5 n/500 g, of which 70.9% exhibited a diameter ranging from 0.038–0.05 mm, while the remaining soil microplastics accounted for less than 20% of all microplastics, indicating that smaller-diameter microplastics were more likely to accumulate in wetland soil. The microplastic abundance could be ranked based on the planting density as follows: 0.5 × 0.5 m > 1.0 × 0.5 m > 1.0 × 1.0 m > control area. Raman spectroscopy revealed that the predominant microplastic categories in this region included polyethylene terephthalate (PET, 52%), polyethylene (PE, 24%) and polypropylene (PP, 15%). Scanning electron microscopy (SEM) images revealed fractures and tears on the surface of microplastics. EDS energy spectra indicated a large amount of metal elements on the surface of microplastics. Due to the adsorptive features of PET, this substance could influence the soil particle size distribution and thus the soil structure. All physicochemical factors, except for the soil pH, were significantly affected by PET. In addition, the CV analysis results indicated that soils in vegetated areas are more susceptible to PET than are soils in bare ground areas, leading to greater variation in their properties.

There is an ongoing demand for region-specific soil organic carbon estimates to support sustainable land management and inform carbon credit programs. The Prairie Pothole Region is prominent agricultural area that extends through Canada and the United States, and features a significant number of wetlands commonly referred to as prairie potholes. The contribution of these wetlands to landscape-level soil organic carbon storage is complex and may not be consistent across the region as influenced by several environmental and management factors. This study reviews existing literature to identify the main factors that contribute to variability in soil organic carbon stocks in prairie pothole wetlands. Soil organic carbon stock data from 10 studies in the Prairie Pothole Region were summarized through a meta-analysis. Variable importance and regression analyses were used to assess which factors explain variability in soil organic carbon. Wetland class explained up to 26.6% of the variability in soil organic carbon. Other important factors included ecoregion as well as land management. There were significant differences in average wetland soil organic carbon stocks across the ecoregions. Data limitations restricted our ability to accurately estimate the stocks for wetland class and land management. The findings from this study highlighted the need for targeted studies in the Northern short grassland ecoregion as well as studies that consider wetland classes under various land uses. To advance wetland carbon research in the Prairie Pothole Region, recommendations were provided on landscape-level carbon modelling, soil carbon measurement and monitoring, and improved wetland classification systems. Graphical Abstract

The effects of Typha latifolia L. on the remediation of cadmium (Cd) in wetland soil were studied using greenhouse pot culture, with soil Cd concentrations of 0, 1, and 30 mg/kg. The T. latifolia showed excellent tolerance to the low and high concentrations of Cd in soil. A higher bioaccumulation of Cd was observed in roots, with bioconcentration factor values of 51.6 and 9.30 at 1 and 30 mg/kg of Cd stress, respectively; Cd concentration in T. latifolia was 77.0 and 410.7 mg/kg, and Cd content was 0.11 and 0.22 mg/plant at the end of the test period. The soil enzyme activities (urease, alkaline phosphatase, and dehydrogenase) exposed to 0, 1, and 30 mg/kg Cd were measured after 0-, 30-, 60-, and 90-day cultivation period and showed an increasing trend with exposure time. Metabolite changes were analyzed using liquid chromatography-mass spectrometry, combined with principal component analysis and orthogonal partial least squares discrimination analysis. Among 102 metabolites, 21 compounds were found and identified, in response to treatment of T. latifolia with different Cd concentrations. The results showed that T. latifolia had a good remedial effect on Cd-contaminated soil. The metabolites of T. latifolia changed with different Cd concentration exposures, as a result of metabolic response of plants to Cd-contaminated soils. Analysis of metabolites could better reveal the pollution remediation mechanism involved in different Cd uptake and accumulate properties.

Strain WRN001T, a Gram-staining-negative, strictly aerobic, non-motile bacterium was isolated from the natural saline-alkali wetland soil of Binhai new district, Tianjin, China (38°46’ N, 117°13’ E). Cells of strain WRN001T were 0.3–0.5 µm in width and 1.5–2.5 µm in length, and the growth occurred optimally at 33–37 °C, pH 7.5–8.0, and in the presence of 8–10% (w/v) NaCl. Based on 16S rRNA gene sequence analysis, the isolate could be affiliated to the genus Halomonas, and the highest 16S rRNA gene sequence similarity of strain WRN001T to its closest relative Halomonas qiaohouensis DSM 26770 T was 97.5%. The size of the genome as presented here was 5,475,884 bp with a G + C content of 63.8 mol %. The major respiratory quinone of strainWRN001T was Q-9, and the dominant fatty acids were summed feature 8, summed feature 3, C10:0, C12:0, C12:0 3-OH, C16:0, and C17:0 cyclo. The major polar lipids were diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phophatidylcholine (PC), two phospholipids (PL), aminolipid (AL), and three unidentified lipids (L). These data combined with the low digital DDH values between strain WRN001T and the close relative, Halomonas alkalitolerans CGMCC 1.9129 T (42.2%) and based on comparisons with currently available genomes, the highest average nucleotide identity (ANIm) value was 91.4% to Halomonas alkalitolerans CGMCC 1.9129 T (GenBank accession No. GCA_001971685.1). Therefore, we propose a novel species in the genus Halomonas to accommodate this novel isolate: Halomonas salipaludis sp. nov. (type strain WRN001T = KCTC 52853 T = ACCC 19974 T).

The purpose of this study was to assess the effects of wetland plant biochars on the enzyme activity in heavy metal contaminated soil. The biochars were produced from Phragmites australis (PB), Suaeda salsa (SB), and Tamarix chinensis (TB) under different pyrolysis temperatures and times. The detected pyrolysis products showed that the ash, pH, electrical conductivity, and carbon content of the biochars increased significantly, while the production rate of the biochars decreased with increasing pyrolysis temperature and time. The results of the adsorption experiments indicated that biochar addition could effectively reduce the concentration of Pb and/or Cd in the Pb 2+ /Cd 2+ single or mixed solutions, but the Pb 2+ and Cd 2+ in the mixed solution indicated a competitive adsorption. A 30-day incubation experiment was conducted using salt marsh soil amended with different biochar application rates to investigate the short-term effects of biochar addition on Pb and Cd immobilization. The PB and SB significantly immobilized Pb within the first 15 days, but Pb remobilized within the next 15-day period. In contrast, TB addition did not significantly fix Pb. Moreover, biochar addition promoted the conversion of Cd from the residue to the less immobile fractions. The addition of three types of plant biochar had no significant effect on the urease activity in wetland soil but significantly increased soil sucrase activity. PB and SB significantly promoted catalase activity, while TB significantly inhibited soil catalase activity. According to the adsorption effect, the fixation effect, and the promotion of enzyme activities, the Suaeda salsa biochars are suitable for the remediation of heavy metal pollution in wetland soils.

Although microorganisms play a key role in the carbon cycle of the Poyang Lake wetland, the relationship between soil microbial community structure and organic carbon characteristics is unknown. Herein, high-throughput sequencing technology was used to explore the effects of water level (low and high levels above the water table) and vegetation types (Persicaria hydropiper and Triarrhena lutarioriparia) on microbial community characteristics in the Poyang Lake wetland, and the relationships between soil microbial and organic carbon characteristics were revealed. The results showed that water level had a significant effect on organic carbon characteristics, and that soil total nitrogen, organic carbon, recombinant organic carbon, particle organic carbon, and microbial biomass carbon were higher at low levels above the water table. A positive correlation was noted between soil water content and organic carbon characteristics. Water level and vegetation type significantly affected soil bacterial and fungal diversity, with water level exerting a higher effect than vegetation type. The impacts of water level and vegetation type were higher on fungi than on bacteria. The bacterial diversity and evenness were significantly higher at high levels above the water table, whereas an opposite trend was noted among fungi. The bacterial and fungal richness in T. lutarioriparia community soil was higher than that in P. hydropiper community soil. Although both water level and vegetation type had significant effects on bacterial and fungal community structures, the water level had a higher impact than vegetation type. The bacterial and fungal community changes were the opposite at different water levels but remained the same in different vegetation soils. The organic carbon characteristics of wetland soil were negatively correlated with bacterial diversity but positively correlated with fungal diversity. Soil water content, soluble organic carbon, C/N, and microbial biomass carbon were the key soil factors affecting the wetland microbial community. Acidobacteria, Alphaproteobacteria, Verrucomicrobia, Gammaproteobacteria, and Eurotiomycetes were the key microbiota affecting the soil carbon cycle in the Poyang Lake wetland. Thus, water and carbon sources were the limiting factors for bacteria and fungi in wetlands with low soil water content (30%). Hence, the results provided a theoretical basis for understanding the microbial-driven mechanism of the wetland carbon cycle.

PurposeWetland soils may face more severe water stress under future climate change. Our aim was to assess the change characteristics of wetland soil bacterial community and metabolic potentials under drought and flood conditions.MethodsWetland soil was incubated under five different water environments (including constant moisture at 30%, natural air-dried, and 3 types of flooding depths) by conducting experimental microcosms. After 1, 21, and 132 days of incubation, the soil bacterial community structure and metabolic potential were examined by the 16S rRNA gene sequencing and Biolog-Ecoplates method, respectively.ResultsThe results showed that Actinobacteria and Firmicutes were significantly enriched under drought and flooding treatments, respectively. Compared to flooding, drought decreased soil microbial biomass and carbon metabolism more severely. However, the depth of flooding did not significantly change bacterial community composition and carbon metabolism. In addition, the responses of soil metabolic functions to drought were more sensitive than the change of bacterial community composition. When the wetland soil faced water stress (drought and flooding), its metabolic functions showed close correlations with bacterial community composition and were negatively affected by most of environmental factors (such as pH, NO3-N, and NH4-N).ConclusionsThe results indicate that the drying condition is more severe and rapid than flooding in threatening soil microbial metabolic activity. In addition, the depth of flooding does not significantly change bacterial community composition and carbon metabolism.

Aims Microbial-driven biogeochemical cycles of phosphorus (P) in wetlands subjected to global climate warming result in a downstream eutrophication risk. However, how warming influences P associated with microbial shifts in wetland soils is largely unknown. Methods A custom-built, novel microcosm that simulated climate warming was established under ambient temperature and elevated wanning conditions (+ 3 °C). 31P nuclear magnetic resonance (31P–NMR) technology was used to characterize different P forms and highthroughput sequencing of 16S rRNA gene was used to identify microbial community and functional potentials in wetland soils varied with nutrition status. Results Soil P forms were dominated by orthophosphate. The dynamic changes of different P forms in response to warming were mainly observed in high nutrition wetlands. The relative abundance of orthophosphate and polyphosphate (inorganic) significantly (p < 0.05) decreased, which was accompanied with increased phosphonate (organic) under warming. Consistently, soil microbial community shifts were also found in high nutrition wetlands, especially in fall with significantly (p < 0.05) increased relative abundance of Alphaproteobacteria and Betaproteobacteria and decreased Clostridia under warming. The microbial functions related to catabolism, the transport, degradation and release of P were enriched under warming. Changed microbial community may have altered the overall functional potentials which were responsible for P dynamics. Conclusions Soil microbial community shifts in response to experimental warming were season-based. Microbial changes and P shifts from high nutrition wetlands were more sensitive to warming. The changed microbial community under warming conditions may trigger the loss of orthophosphate through the altered functional potentials. These findings aid to better understand microbial-driven biogeochemical cycles of P in wetland soils under future climate changes.

Soil amendments have been proposed as a means to speed the development of plant and soil processes that contribute to water quality, habitat, and biodiversity functions in restored wetlands. However, because natural wetlands often act as significant methane sources, it remains unknown if amendments will also stimulate emissions of this greenhouse gas from restored wetlands. In this study, we investigated the potential trade-offs of incorporating soil amendments into wetland restoration methodology. We used controlled field-scale manipulations in four recently restored depressional freshwater wetlands in western New York, USA to investigate the impact that soils amended with organic materials have on water-quality functions and methane production in the first three years of development. Results showed that amendments, topsoil in particular, were effective for stimulating the development of a suite of biological (microbial biomass increased by 106% and respiration by 26%) and physicochemical (cation exchange capacity increased by 10%) soil properties indicative of water-quality functions. Furthermore, increases in microbial biomass and activity lasted for a significantly longer period of time (years instead of days) than studies examining less recalcitrant amendments. However, amended plots also had 20% times higher potential net methane production than control plots three years after restoration. Wetlands restoration projects are implemented to achieve a variety of goals, commonly including habitat provision, biodiversity, and water-quality functions, but also carbon sequestration, flood abatement, cultural heritage and livelihood preservation, recreation, education, and others. Projects should strive to achieve their specific goals while also evaluating the potential tradeoffs between wetland functions.