Composition and assembly mechanisms of prokaryotic communities in wetlands, and their relationships with different vegetation and reclamation methods

Nonuniform organic carbon stock loss in soils across disturbed blue carbon ecosystems

Conserving blue carbon ecosystems (BCEs) has gained international attention in climate change mitigation, reflected in United Nations policies and voluntary carbon-offset projects. These efforts assume significant and uniform losses of soil organic carbon (Corg) throughout the top meter following disturbances, yet this assumption lacks robust empirical support. Here, we synthesized 239 paired observations of intact and disturbed BCEs globally. Soil Corg stock losses in the top meters vary widely: from -68.4% (agricultural conversion, ±13.4%, 95% confidence interval) to +0.8% (harvesting, ±46.2%) in mangroves, -25.9% (climate/hydrological change, ± 30.7%) to +48.6% (grazing, ±78.7%) in saltmarshes, and -34.2% (vegetation cover damage, ±22.4%) to -27.4% (dredging, ±33.6%) in seagrasses. Extensive disturbances deplete Corg down to 50-200 cm, while limited disturbances impact only the top 10-30 cm or resulted in negligible losses. This refinement contributes to improved global inventories of greenhouse gas emissions from BCEs, supporting abatement policy settings for nationally determined contributions commitments.

Habitat preference drives the community composition, beta diversity and assembly processes of benthic diatoms: A case study of a wetland cluster in a cold region

The loss of biodiversity in urban wetlands has become increasingly severe due to urbanization. Based on their attachment patterns, benthic diatoms can be divided into several types according to habitat (i.e., epilithic, epiphytic, and epipelic). Diatoms are often used as ecological indicators due to their sensitivity to environmental changes. However, details concerning the composition, temporal dynamics, and assembly mechanisms of benthic diatom communities in urban wetland habitats remain unclear. In this study, we systematically evaluated the composition and seasonal dynamics of benthic diatoms among three different habitats and validated the applicability of eDNA for studies of diatoms. The relationship between the taxonomic and functional diversity of diatom communities was examined, and the assembly mechanisms of diatom communities were explored. An analysis of 249 benthic diatom samples and 27 water samples from nine sites over eight months revealed differences in the composition of diatom communities among epilithic, epiphytic, and epipelic habitats. In diatoms from different hydrological periods, the contribution of turnover to total taxonomic beta diversity was much larger than that of nestedness, while the nestedness components of functional diversity were comparatively large. Nutrients, total dissolved solids, and water temperature were the main variables that affected the taxonomic and functional beta diversity of the benthic diatom communities. The results suggested that benthic diatom community assembly in the three habitats and eDNA was primarily driven by deterministic processes. This study has demonstrated how habitat preference affects the composition, beta diversity and assembly processes of benthic diatom communities and provided novel insights into the conservation of biodiversity in urban wetlands.

Metagenomic deciphers the mobility and bacterial hosts of antibiotic resistance genes under antibiotics and heavy metals co-selection pressures in constructed wetlands

Both antibiotics and heavy metals exert significant selection pressures on antibiotic-resistance genes (ARGs). This study aimed to investigate the co-selection effects of doxycycline (DC) and cadmium (Cd) on ARGs in constructed wetlands (CWs). The results demonstrated that under antibiotic and heavy metal co-selection pressures, single high concentration DC/Cd or double high, relative abundances of metagenomics assembled genomes all reached 55.1%; meanwhile, the average ratio of ARG-containing contigs located on chromosomes was 61.8% (ranging from 50.4% to 70.6%) suggesting a more stable inheritance of ARGs. Antibiotic and heavy metal co-selection in single high concentration DC/Cd or double high groups stimulate the enrichment of ARG host bacteria, which exhibited complex multiple-resistant patterns accompanied by a host-specific pattern. Additionally, the potential transfer abilities of ARGs mediated by plasmids and integrative and conjugative elements (ICEs) were enhanced under single high-concentration DC/Cd or double high stresses. Together, antibiotic and heavy metal co-selection pressures increased occurrence frequencies of ARGs, MGEs, and their combinations and altered structural communities of ARG host bacteria, increasing the risk of the spread of ARGs. This study was helpful in understanding the dissemination of ARGs and simultaneously preventing the spread of heavy metal-resistant bacteria and ARGs under antibiotic and heavy metal co-selection in small- and micro-wetlands.

Spartina alterniflora invasion significantly alters the assembly and structure of soil bacterial communities in the Yellow River Delta

Soil microbial communities are integral to almost all terrestrial biogeochemical cycles, which are essential to coastal wetland functioning. However, how soil bacterial community assembly, composition, and structure respond to native and non-native plant invasions in coastal wetlands remains unclear. In this study of the coastal wetlands of the Yellow River Delta in China, the assembly, community composition, and diversity of soil bacterial communities associated with four wetland plant species (Phragmites australis, Spartina alterniflora, Suaeda salsa, and Tamarix chinensis) and four soil depths (0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm) were characterized using high-throughput sequencing. Plant species identity, as well as environmental factors, rather than soil depth, was found to play predominant roles in shaping the diversity and structure of wetland soil bacterial communities. S. alterniflora invasion altered bacterial community structure and increased bacterial diversity. Phragmites australis-associated bacterial communities were enriched with sulfate-reducing bacteria such as Desulfurivibrio and Desulfuromonas. In comparison, S. alterniflora-associated bacterial communities were enriched with both sulfate-reducing bacteria (SEEP-SRB1) and sulfate-oxidizing bacteria (Sulfurimonas), which maintained a dynamic balance in the local sulfur-cycle, and thereby enhanced S. alterniflora growth. In addition, stochastic processes dominated the assembly of soil bacterial communities associated with all four plant species, but were most important for the S. alterniflora community. The S. alterniflora-associated bacterial community also showed stronger interactions and more extensive connections among bacterial taxa; a co-occurrence network for this community had the greatest average clustering coefficient, average degree, modularity, and number of links and nodes, but the lowest average path length. Altogether, individual plant species had distinct effects on soil bacterial community assembly and structure, with the invasive species having the strongest impact. These results provide insights into microbial ecology and inform management strategies for coastal wetland restoration.

Scale effects on the accuracy and result of soil nitrogen mapping in coastal areas of northern China

The scale effect is crucial for soil mapping because by influencing the simulation accuracy and results. To date, the scale effect on soil mapping in coastal areas remains unclear, and changes in simulation accuracy and results across multiple scales are urgently to be uncovered. The present study aimed to reveal the scale effects of surface soil total nitrogen mapping over large-extent coastal areas. The northern China's coastal areas were selected as the spatial extent, and two time points in 2010 and 2020 were considered the temporal interval. Ten spatial scales from 100 m to 1000 m were used as the simulation units. Results indicated a distinct increase in soil nitrogen in most of the study area during 2010-2020, and the surface soil total nitrogen density and storage were 0.256 kg/m2 and 16.67 Tg in 2020, increasing by 17.18% and 18.60%, respectively, in the entire study area. This increase was mainly driven by promoting ecological quality through extensive ecological restorations in China. Across the 10 scales, the highest simulation accuracy was achieved by the 200 m scale with a root mean squared error of 0.4217 and Lin's concordance correlation coefficient of 0.4193. The simulation results were similar in the extent of the entire study area but changed considerably in the degree and nature in the extent of small geographical regions. The scale effect on the simulation results increased with the decrease in the area of the analyzed extent and was more distinct in areas with lower soil nitrogen. The study has quantitatively delineated the scale effects on simulation accuracy and results in coastal soil nitrogen mapping and can effectively guide the resolution selection for different mapping extents and demands. Generally, the coarse spatial resolution (1000 m) homogenized the simulation results and was a relatively feasible scale with a low cost at a large extent. In contrast, the fine resolution (100 m and 200 m) presented high spatial heterogeneity and was essential for precise simulation results at a small extent. The 200 m scale is recommended in coastal soil nitrogen mapping under normal circumstances for its highest accuracy of the 10 scales and distinctly lower cost compared with the 100 m scale.

Anthropogenic restoration exhibits more complex and stable microbial co-occurrence patterns than natural restoration in rubber plantations

Forest restoration is an effective method for restoring degraded soil ecosystems (e.g., converting primary tropical forests into rubber monoculture plantations; RM). The effects of forest restoration on microbial community diversity and composition have been extensively studied. However, how rubber plantation-based forest restoration reshapes soil microbial communities, networks, and inner assembly mechanisms remains unclear. Here, we explored the effects of jungle rubber mixed (JRM; secondary succession and natural restoration of RM) plantation and introduction of rainforest species (AR; anthropogenic restoration established by mimicking the understory and overstory tree species of native rainforests) to RM stands on soil physico-chemical properties and microbial communities. We found that converting tropical rainforest (RF) to RM decreased soil fertility and simplified microbial composition and co-occurrence patterns, whereas the conversion of RM to JRM and AR exhibited opposite results. These changes were significantly correlated with pH, soil moisture content (SMC), and soil nutrients, suggesting that vegetation restoration can provide a favorable soil microenvironment that promotes the development of soil microorganisms. The complexity and stability of the bacterial-fungal cross-kingdom, bacterial, and fungal networks increased with JRM and AR. Bacterial community assembly was primarily governed by stochastic (78.79 %) and deterministic (59.09 %) processes in JRM and AR, respectively, whereas stochastic processes (limited dispersion) predominantly shaped fungal assembly across all forest stands. AR has more significant benefits than JRM, such as a relatively slower and natural vegetation succession with more nutritive soil conditions, microbial diversity, and complex and stable microbial networks. These results highlight the importance of sustainable forest management to restore soil biodiversity and ecosystem functions after extensive soil degradation and suggest that anthropogenic restoration can more effectively improve soil quality and microbial communities than natural restoration in degraded rubber plantations.

Effects of biodiversity on functional stability of freshwater wetlands: a systematic review

Freshwater wetlands are the wetland ecosystems surrounded by freshwater, which are at the interface of terrestrial and freshwater ecosystems, and are rich in ecological composition and function. Biodiversity in freshwater wetlands plays a key role in maintaining the stability of their habitat functions. Due to anthropogenic interference and global change, the biodiversity of freshwater wetlands decreases, which in turn destroys the habitat function of freshwater wetlands and leads to serious degradation of wetlands. An in-depth understanding of the effects of biodiversity on the stability of habitat function and its regulation in freshwater wetlands is crucial for wetland conservation. Therefore, this paper reviews the environmental drivers of habitat function stability in freshwater wetlands, explores the effects of plant diversity and microbial diversity on habitat function stability, reveals the impacts and mechanisms of habitat changes on biodiversity, and further proposes an outlook for freshwater wetland research. This paper provides an important reference for freshwater wetland conservation and its habitat function enhancement.

Patterns of bacterial distance decay and community assembly in different land-use types as influenced by tillage management and soil layers

Land use and cover change are major factors driving global change and greatly impact terrestrial organisms, especially soil microbial diversity. Little is known, however, about bacterial diversity, distribution patterns and assembly processes across different land use types. In this study, therefore, we conducted a large-scale field survey of 48 sampling sites, encompassing different land use types in Xuancheng city, China, with different degrees of soil disturbance and different soil horizons. The distance-decay relationships (DDRs), assembly processes and the spatial patterns of soil bacterial communities were investigated based on high-throughput sequencing data. We found that the DDRs might be weakened by anthropogenic disturbances, which were not observed in tilled soils, while a decreasing trend was observed along the soil horizon in untilled soils. The relative importance of environmental factors and geographic distance varied with soil tillage. Specifically, bacterial communities in tilled soils were driven by non-spatially autocorrelated environmental factors, while untilled soils were more susceptible to geographic distance. In addition, the heterogeneity of soil properties, as well as the differences in soil bacterial niche width and niche overlap, determined the assembly processes of the bacterial community, resulting in opposite trends along the soil layers in tilled and untilled soils. These findings expand the current understanding of the biogeography of soil bacterial communities across different land use types.