Anti-seasonal submergence dominates the structure and composition of prokaryotic communities in the riparian zone of the Three Gorges Reservoir, China

Risk assessment of exposure to 12 kinds of mycotoxins through consumption of Pericarpium Citri Reticulatae collected from Three Gorges Reservoir area of China

A method for simultaneous determination of 12 mycotoxins in Pericarpium Citri Reticulataeby HPLC-MS/MS was established to analyze the residues of mycotoxins, inwhich from Three Gorges Reservoir area of China, including AFB1, AFB2, AFG1, AFG2, T-2, FB1, FB2, FB3, ZEN, OTA, OTB and DON.In addition, a probabilistic assessment model based on Monte Carlo simulation method was established in combination with pollution data, and the health risk assessment was carried out by the exposure limit method (MOE).The results showed that the method with strong specificity, good linearity and accurate recovery was established and could be used for the determination of 12 mycotoxins in Pericarpium Citri Reticulatae.In general, the total pollution rate of different degrees of pollution in the 36 batches of Pericarpium Citri Reticulatae sampleswas 75 %. It should be noted thatthe proportion of positive samplescontaminated by one toxin was the highest (59.26 %), and the detection rate of FB3 in Pericarpium Citri Reticulataewas the highest (66.67%), followed by AFG1 (44.44 %), indicating that the medicinal material polluted by AFG1 and AFB3 alone or simultaneously was more serious. Specifically, the detection rate of mycotoxins in Chongqing was the highest (92.31%) on account of the high temperature and humidity in Chongqing, followed by Southeast of Sichuan (83.33%) and West of Hubei (45.45%).On the other hand, the MOE of AFB1 and AFB2 calculated were both greater than 10000, indicating that the health risk of AFB1 and AFB2 exposure caused by taking Pericarpium Citri Reticulatae was low, but the risk of high intake population was higher than that of conventional intake population, which needed to be paid attention to. This study can provide a reference for the safety assessment of clinical medication of Pericarpium Citri Reticulatae inThree Gorges Reservoir area.

Shifts of soil archaeal nitrification and methanogenesis with elevation in water level fluctuation zone of the three Gorges Reservoir, China

The water level fluctuation zone is a unique ecological zone exposed to long-term drying and flooding and plays a critical role in the transport and transformation of carbon and nitrogen materials in reservoir-river systems. Archaea are a vital component of soil ecosystems in the water level fluctuation zones, however, the distribution and function of archaeal communities in responde to long-term wet and dry alternations are still unclear. The community structure of archaea in the drawdown areas at various elevations of the Three Gorges Reservoir was investigated by selecting surface soils (0-5 cm) of different inundation durations at three sites from upstream to downstream according to the flooding pattern. The results revealed that prolonged flooding and drying increased the community diversity of soil archaea, with ammonia-oxidizing archaea being the dominant species in non-flooded regions, while methanogenic archaea were abundant in soils that had been flooded for an extended period of time. Long-term alternation of wetting and drying increases methanogenesis but decreases nitrification. It was determined that soil pH, NO3--N, TOC and TN are significant environmental factors affecting the composition of soil archaeal communities (P = 0.02). Long-term flooding and drying changed the community composition of soil archaea by altering environmental factors, which in turn influenced nitrification and methanogenesis in soils at different elevations. These findings contribute to our understanding of soil carbon and nitrogen transport transformation processes in the water level fluctuation zone as well as the effects of long-term wet and dry alternation on soil carbon and nitrogen cycles. The results of this study can provide a basis for ecological management, environmental management, and long-term operation of reservoirs in water level fluctuation zones.

Explore the soil factors driving soil microbial community and structure in Songnen alkaline salt degraded grassland

Introduction

Saline-alkali degradation in grassland significantly affects plant community composition and soil physical and chemical properties. However, it remains unclear whether different degradation gradients affect soil microbial community and the main soil driving factors. Therefore, it is important to elucidate the effects of saline-alkali degradation on soil microbial community and the soil factors affecting soil microbial community in order to develop effective solutions to restore the degraded grassland ecosystem.

Methods

In this study, Illumina high-throughput sequencing technology was used to study the effects of different saline-alkali degradation gradients on soil microbial diversity and composition. Three different gradients were qualitatively selected, which were the light degradation gradient (LD), the moderate degradation gradient (MD) and the severe degradation gradient (SD).

Results

The results showed that salt and alkali degradation decreased the diversity of soil bacterial and fungal communities, and changed the composition of bacterial and fungal communities. Different degradation gradients had different adaptability and tolerance species. With the deterioration of salinity in grassland, the relative abundance of Actinobacteriota and Chytridiomycota showed a decreasing trend. EC, pH and AP were the main drivers of soil bacterial community composition, while EC, pH and SOC were the main drivers of soil fungal community composition. Different microorganisms are affected by different soil properties. The changes of plant community and soil environment are the main factors limiting the diversity and composition of soil microbial community.

Discussion

The results show that saline-alkali degradation of grassland has a negative effect on microbial biodiversity, so it is important to develop effective solutions to restore degraded grassland to maintain biodiversity and ecosystem function.

Diversity and assembly of active bacteria and their potential function along soil aggregates in a paddy field

Numerous studies have found that soil microbiomes differ at the aggregate level indicating they provide spatially heterogeneous habitats for microbial communities to develop. However, an understanding of the assembly processes and the functional profile of microbes at the aggregate level remain largely rudimentary, particularly for those active members in soil aggregates. In this study, we investigated the diversity, co-occurrence network, assembly process and predictive functional profile of active bacteria in aggregates of different sizes using H₂¹⁸O-based DNA stable isotope probing (SIP) and 16S rRNA gene sequencing. Most of the bacterial reads were active with 91 % of total reads incorporating labelled water during the incubation. The active microbial community belonged mostly of Proteobacteria and Actinobacteria, with a relative abundance of 55.32 % and 28.12 %, respectively. Assembly processes of the active bacteria were more stochastic than total bacteria, while the assembly processes of total bacteria were more influenced by deterministic processes. Furthermore, many functional profiles such as environmental information processing increased in active bacteria (19.39 %) compared to total bacteria (11.22 %). After incubation, the diversity and relative abundance of active bacteria of certain phyla increased, such as Proteobacteria (50.70 % to 59.95 %), Gemmatimonadetes (2.63 % to 4.11 %), and Bacteroidetes (1.50 % to 2.84 %). In small macroaggregates (SMA: 0.25-2 mm), the active bacterial community and its assembly processes differed from that of other soil aggregates (MA: microaggregates, <0.25 mm; LMA: large macroaggregates, 2-4 mm). For functional profiles, the relative abundance of important functions, such as amino acid metabolism, signal transduction and cell motility, increased with incubation days and/or in SMA compared to other aggregates. This study provides robust evidence that the community of active bacteria and its assembly processes in soil aggregates differed from total bacteria, and suggests the importance of dominant active bacteria (such as Proteobacteria) for the predicted functional profiles in the soil ecosystem.

Fungi and cercozoa regulate methane-associated prokaryotes in wetland methane emissions

Wetlands are natural sources of methane (CH₄) emissions, providing the largest contribution to the atmospheric CH₄ pool. Changes in the ecohydrological environment of coastal salt marshes, especially the surface inundation level, cause instability in the CH₄ emission levels of coastal ecosystems. Although soil methane-associated microorganisms play key roles in both CH₄ generation and metabolism, how other microorganisms regulate methane emission and their responses to inundation has not been investigated. Here, we studied the responses of prokaryotic, fungal and cercozoan communities following 5 years of inundation treatments in a wetland experimental site, and molecular ecological networks analysis (MENs) was constructed to characterize the interdomain relationship. The result showed that the degree of inundation significantly altered the CH₄ emissions, and the abundance of the pmoA gene for methanotrophs shifted more significantly than the mcrA gene for methanogens, and they both showed significant positive correlations to methane flux. Additionally, we found inundation significantly altered the diversity of the prokaryotic and fungal communities, as well as the composition of key species in interactions within prokaryotic, fungal, and cercozoan communities. Mantel tests indicated that the structure of the three communities showed significant correlations to methane emissions (p < 0.05), suggesting that all three microbial communities directly or indirectly contributed to the methane emissions of this ecosystem. Correspondingly, the interdomain networks among microbial communities revealed that methane-associated prokaryotic and cercozoan OTUs were all keystone taxa. Methane-associated OTUs were more likely to interact in pairs and correlated negatively with the fungal and cercozoan communities. In addition, the modules significantly positively correlated with methane flux were affected by environmental stress (i.e., pH) and soil nutrients (i.e., total nitrogen, total phosphorus and organic matter), suggesting that these factors tend to positively regulate methane flux by regulating microbial relationships under inundation. Our findings demonstrated that the inundation altered microbial communities in coastal wetlands, and the fungal and cercozoan communities played vital roles in regulating methane emission through microbial interactions with the methane-associated community.

Microbial community and soil enzyme activities driving microbial metabolic efficiency patterns in riparian soils of the Three Gorges Reservoir

Riparian zones represent important transitional areas between aquatic and terrestrial ecosystems. Microbial metabolic efficiency and soil enzyme activities are important indicators of carbon cycling in the riparian zones. However, how soil properties and microbial communities regulate the microbial metabolic efficiency in these critical zones remains unclear. Thus, microbial taxa, enzyme activities, and metabolic efficiency were conducted in the riparian zones of the Three Gorges Reservoir (TGR). Microbial carbon use efficiency and microbial biomass carbon had a significant increasing trend along the TGR (from upstream to downstream); indicating higher carbon stock in the downstream, microbial metabolic quotient (qCO₂) showed the opposite trend. Microbial community and co-occurrence network analysis revealed that although bacterial and fungal communities showed significant differences in composition, this phenomenon was not found in the number of major modules. Soil enzyme activities were significant predictors of microbial metabolic efficiency along the different riparian zones of the TGR and were significantly influenced by microbial α-diversity. The bacterial taxa Desulfobacterota, Nitrospirota and the fungal taxa Calcarisporiellomycota, Rozellomycota showed a significant positive correlation with qCO₂. The shifts in key microbial taxa unclassified_k_Fungi in the fungi module #3 are highlighted as essential factors regulating the microbial metabolic efficiency. Structural equation modeling results also revealed that soil enzyme activities had a highly significant negative effect on microbial metabolism efficiency (bacteria, path coefficient = -0.63; fungi, path coefficient = -0.67).This work has an important impact on the prediction of carbon cycling in aquatic-terrestrial ecotones. Graphical abstract.

Photovoltaic panels have altered grassland plant biodiversity and soil microbial diversity

Introduction

Human concerns about fossil fuel depletion, energy security and environmental degradation have driven the rapid development of solar photovoltaic (PV) power generation. Most of the photovoltaic power generation plants are concentrated in desert, grassland and arable land, which means the change of land use type. However, there is still a gap in the research of the PV panel layout on grassland plant species diversity and ecological function.

Methods

In this study, Illumina high-throughput sequencing technology was used to investigate the effects of PV panel arrangement on grassland plant species diversity and soil microbial diversity. In view of the differences in the microclimate at different sites of the PV panels, quadrates were arranged in front edge (FE), beneath the center of each panel (BP), back edge (BE), the uncovered interspace adjacent to each panel (IS) and the undisturbed grassland around the PV panels (Control), respectively.

Results

PV panels (especially FE) significantly increased the total aboveground productivity (total AGB) and plant species diversity in grasslands. FE increased precipitation accumulation and plant species diversity directly and indirectly changed the diversity of soil bacterial and fungal communities. PV panels decreased the relative abundance of Actinobacteriota, while increased the relative abundance of Proteobacteria, Acidobacteriota, and Methylomirabilota. EC, Margalef' s richness and total AGB were the main factors affecting the composition of bacterial communities, while alkaline hydrolysis nitrogen (AN) and available phosphorus (AP) were the main factors affecting the composition of fungal communities.

Discussion

In conclusion, the arrangement of PV panels increased the plant species diversity and soil microorganisms in grassland. This study provides important information for further understanding the impact of PV panels on grassland ecosystem function and is of great significance for maintaining grassland ecosystem function.

Regulating autogenic vegetation in the riparian zone reduces carbon emissions: Evidence from a microcosm study

Riparian zones have been found to be hot spots of greenhouse gas (GHG) production and have attracted increasing attention in recent decades. The occurrence of autogenic vegetation in riparian zones is prevalent, but little information is available concerning the influence of the occurrence and decomposition of this vegetation on carbon mitigation. We conducted a 220-day (110 days for the dry season and 110 days for the flooded season) microcosm experiment to study the mitigation and transformation of carbon regulated by the vegetation. The results revealed that there was a carbon dioxide (CO₂) flux in the treatment with vegetation, and that without vegetation harvesting (835.58 mg/m²/h) was close to that with vegetation harvesting (796.22 mg/m²/h) under the simulated dry season conditions, but it was significantly higher than that without vegetation seedlings (411.55 mg/m²/h). After being flooded, the decomposition of the vegetation residues increased the total organic carbon (TOC) content of the sediment, the dissolved organic carbon (DOC) concentration of the water, and the dissolved CO₂ and methane (CH₄) contents of the sediment. This effect was reversed by harvesting the vegetation biomass. During the flooded season, the CO₂ flux reached 222.95 mg/m²/h in the vegetation seeded treatment, but it decreased to -53.71 mg/m²/h when the vegetation biomass was harvested before being submerged. This was due to the decrease in the substrate available for CO₂ production, the altered microorganism communities, and the decrease in the abundance of carbon metabolizing related enzymes. As a result, vegetation harvesting reduced the net carbon emissions by 48 % compared to that without vegetation regulation during the 220-day incubation period. The results of this study are significant to implementing measures to reduce GHG emissions from the riparian zone.

Dam-induced difference of invasive plant species distribution along the riparian habitats

Riparian ecosystem is structurally unstable due to the frequent disturbances from water fluctuation. Moreover, dams on large rivers tend to trigger fundamental changes of the composition and structure of riparian plant communities, which provides high odds for invasive species to colonize. Yet, how the invasive species distribute along a dam-induced riparian habitat, and how the native species resist to plant invasion are still puzzles. In this study, we investigated spatial distribution of invasive floral species and its correlation with the distance from dam and the dam-triggered flooding stresses, as well as the resistance of native species to plant invasion in the water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) along the Yangtze River. By our investigation, a total of 43 alien plant species belonging to 14 families and 34 genera were found, including 20 existed and 23 newly discovered alien species recorded. Most of the new invasive species are annual herbs of the Asteraceae family. At the current successional stage, the new invasive species had not yet fully occupied the habitats of the existed invasive species. Longitudinally, number and coverages of the new invasive species showed an opposite distribution pattern to the existed invasive species, but vertically they demonstrated similar pattern. Currently, the new dominant invasive species are mainly concentrated at the intermediate elevation of WLFZ in the middle section of the reservoir, whereas the existed dominant invasive species have proliferated across the whole WLFZ. Additionally, native species showed a weak resistance to plant invasion, and water fluctuation along the elevation exerted the most significant influence on plant invasion. The results indicated that, after a decade of riparian community succession, the invasiveness of alien species remain persisted. The potential penetration site of the invasion may locate at the intermediate section along the vertical and longitudinal dimension.

Effects of Land-Use Type and Flooding on the Soil Microbial Community and Functional Genes in Reservoir Riparian Zones

Ecological processes (e.g., nutrient cycling) in riparian zones are often affected by land-use type and flooding. The extent to which land-use types and flooding conditions affect soil microorganisms and their ecological functions in riparian zones is not well known. By using high-throughput sequencing and quantitative PCR (q-PCR), we tested the effects of three land-use types (i.e., forest, wetland, and grassland) and two flooding conditions (i.e., landward locations and waterward locations within the land-use types) on soil microbial communities and microbial functional genes in the riparian zones of a reservoir. Land-use type but not flooding significantly affected soil microbial community composition at the phylum level, while both land-use type and flooding significantly affected the orders Nitrosotaleales and Nitrososphaerales. Alpha diversity was higher in the wetland and forest regardless of flooding conditions. Functional gene abundance differed among the three land-use types. Archaeal amoA (AOA) and nirS genes were more abundant in the wetland than in the grassland or forest. Bacterial amoA (AOB), nirK, nirS, and nosZ genes were more abundant in the waterward location than in the landward location but only in the wetland. Soil pH, moisture, and concentrations of soil organic matter and total soil nitrogen were significantly associated with the composition of archaeal and bacterial communities as well as with their gene abundance. This study revealed that soil microorganisms putatively involved in nitrogen cycling in riparian zones were more affected by land-use type than flooding.

Soil CO2 and CH4 emissions and their carbon isotopic signatures linked to saturated and drained states of the Three Gorges Reservoir of China

Human activities such as dams disturb the structure and function of wetlands, triggering large soil CO₂ and CH₄ emissions. However, controls over field CO₂ and CH₄ emissions and their carbon isotopic signatures in reservoir wetlands are not yet fully understood. We investigated in situ CO₂ and CH₄ emissions, the δ¹³C values of CO₂ and CH₄, and associated environments in the saturated and drained states under four elevations (i.e., the water column, <147 m, permanent inundation area without plants; the low, 145-160 m, frequently flooded area with revegetation; the high, 160-175 m, rarely flooded area with revegetation; and the upland area as the control, >175 m, nonflooded area with original plants) in the Three Gorges Reservoir area. The CO₂ emissions was significantly higher in high elevation, and they also significantly differed between the saturated and drained states. In contrast, the CH₄ emissions on average (41.97 μg CH₄ m^-2 h^-1) were higher at high elevations than at low elevations (22.73 μg CH₄ m^-2 h^-1) during the whole observation period. CH₄ emissions decreased by 90% at low elevations and increased by 153% at high elevations from the saturated to drained states. The δ¹³C of CH₄ was more enriched at high elevations than in the low and upland areas, with a more depleted level under the saturated state than under the drained state. We found that soil CO₂ and CH₄ emissions were closely related to soil substrate quality (e.g., C: N ratio) and enzyme activities, whereas the δ¹³C values of CO₂ and CH₄ were primarily associated with root respiration and methanogenic bacteria, respectively. Specifically, the effects of the saturated and drained states on soil CO₂ and CH₄ emissions were stronger than the effect of reservoir elevation, thereby providing an important basis for assessing carbon neutrality in response to anthropogenic activities.

Geographical Distribution of Iron Redox Cycling Bacterial Community in Peatlands: Distinct Assemble Mechanism Across Environmental Gradient

Microbial-mediated iron (Fe) oxidation and reduction greatly contribute to the biogeochemistry and mineralogy of ecosystems. However, knowledge regarding the composition and distribution patterns of iron redox cycling bacteria in peatlands remains limited. Here, using high-throughput sequencing, we compared biogeographic patterns and assemblies of the iron redox cycling bacterial community between soil and water samples obtained from different types of peatland across four regions in Northeast China. A total of 48 phylotypes were identified as potential iron redox bacteria, which had greater than 97% similarity with Fe(II)-oxidizing bacteria (FeOB) and Fe(III)-reducing bacteria (FeRB). Among them, Rhodoferax, Clostridium, Geothrix, Sideroxydans, Geobacter, Desulfovibrio, and Leptothrix could be used as bioindicators in peatlands for characterizing different hydrological conditions and nutrient demands. Across all samples, bacterial communities associated with iron redox cycling were mainly affected by pH, dissolved organic carbon (DOC), and Fe²⁺. Distance-decay relationship (DDR) analysis indicated that iron redox cycling bacterial communities in soil, but not in water, were highly correlated with geographic distance. Additionally, null model analysis revealed that stochastic processes substituted deterministic processes from minerotrophic fens to ombrotrophic bogs in soils, whereas deterministic processes were dominant in water. Overall, these observations suggest that bacteria involved in iron redox cycling are widespread in diverse habitats and exhibit distinct patterns of distribution and community assembly mechanisms between soil and water in peatlands.

Flooding variations affect soil bacterial communities at the spatial and inter-annual scales

Hydrological variations have substantial effects on the diversity and composition of soil bacterial communities in wetlands. At the spatial scale, the responses of soil bacterial diversity and composition to hydrological variations in wetlands have been extensively investigated. However, at the temporal scale, especially at the inter-annual scale, the corresponding bacterial responses are rarely reported. Therefore, we explored the effects of flooding variations on the diversity and composition of soil bacterial communities at a lakeshore wetland in two hydrological contrasting years. Three flooding variables, i.e. flooding duration (FD), total duration of the growing season (TGD), and exposure duration of the growing season (EGD), were used to characterize flooding regime. Soil bacterial communities were determined using 16S rRNA gene sequencing method. We found a very high soil bacterial diversity at the lakeshore wetland. The Shannon's indexes of soil bacterial communities varied from 5.61 to 7.11 in two years. Soil bacterial α-diversity followed a unimodal curve along the elevation gradient, and was significantly lower in the flooding year than in the drought year. Principal coordinate analysis demonstrated that the compositions of soil bacterial communities were separated in order of elevation and year along the first and second axes, respectively. The apparent habitat preferences of soil bacterial families were closely connected with their respiratory traits, and this trend was stronger at the inter-annual scale than at the spatial scale. Soil bacterial compositions were predominantly determined by the direct (by changing respiratory traits) and indirect (by changing soil pH) effects of TGD at the spatial scale, while they were simultaneously regulated by the direct effects of three flooding variables at the inter-annual scale. Our results enhance the understanding of soil microbial communities in wetlands and have large implications for developing general theories to predicting soil microbial functions.

The bacterial community structure and N-cycling gene abundance in response to dam construction in a riparian zone

Dam construction has significantly altered riparian hydrological regime and environmental conditions in the reservoir region, yet knowledge concerning how bacterial community and N-cycling genes respond to these changes remains limited. In this study, we investigated the bacterial community composition, network structure and N-cycling genes in the water level fluctuation zones (WLFZs) of the Three Gorges Reservoir (TGR). Here, samples collected from five different water levels were divided into three groups: waterward sediments, interface sediments, and landward soils. Our results show that higher contents of NO₂^--N, SOC, DOC, NH₄⁺-N, and TP were characterized in waterward and interface sediments whereas higherNO₃^--N content was observed in landward soils. The α-diversity of bacterial community decreased gradually from waterward sediments to landward soils. Compared with waterward sediments and landward soils, the interface sediments showed a unique bacterial community pattern with diverse primary producers as well as N-cycling microbes. The interface sediments also had a much more complex co-occurrence network and a higher possible community stability. Among all of N-cycling genes, higher abundances of nrfA and AOA amoA genes were observed in interface sediments. The dissimilarity in bacterial community composition and N-cycling gene abundance was mainly driven by water-level. Moreover, random forest model revealed that AOA amoA and nirS genes were the most sensitive indicators in response to water level fluctuations. Overall, this study suggests distinct abundance, diversity, and network structure of microbes in riparian sediments and soils across the gradient of water levels and enhances our understanding with respect to comprehensive effects of dam construction on nitrogen cycle.

Dramatic change of bacterial assembly process and co-occurrence pattern in Spartina alterniflora salt marsh along an inundation frequency gradient

Exotic Spartina alterniflora has become widely distributed along most of the coastlines in China in a wide range of inundation frequencies. However, the assembly processes and co-occurrence patterns of the bacterial community in S. alterniflora wetlands under different inundation frequencies remain elusive. In this study, an in-situ mesocosm was established to investigate the changes in soil bacterial community. We found that soil water content was the most decisive factor in influencing the bacterial community. Balanced variation, rather than abundance gradients, accounted for the major shifts in bacterial communities and was significantly and positively correlated with the changes in water content, suggesting that species substitution was facilitated by the increased water content. Deterministic processes were dominant in community assembly, and a large degree of change in water content increased variable selection. Co-occurrence network revealed that increasing water content significantly decreased the average degree and the relative abundance of keystone species, resulting in a network with less complexity. Structural equation modelling suggests that increasing inundation frequency has strong impacts on bacterial community, primarily by altering water content, network degree, and the relative abundance of keystone species. Overall, our results illustrate that increasing inundation frequency significantly influences the bacterial community assembly processes and co-occurrence patterns.

Shift in functional plant groups under flooding impacted ecosystem C and N dynamics across riparian zones in the Three Gorges of China

Large water conservancy project can strongly alter the plant community composition, however, how these changes can potentially affect ecosystem carbon (C) and nitrogen (N) dynamics is not fully understood. Here, we investigated natural ¹³C and ¹⁵N abundance of C₃ and C₄ plants and soil in different fractions [labile C (LC) and N (LN), recalcitrant C (RC) and N (RN)]from 6 sites with two elevations (flooding zone, 145-175 m, area with revegetation due to flooding, N = 6); and unflooding zone, >175 m with original plant as a control, N = 3) in riparian zones of the Three Gorges Reservoir, China. The dominant species were the C₄ plants in the upstream including Changshou (CS), Fuling (FL) and Zhongxian (ZX) and the C₃ plants in the downstream in unflooding zone including Wanzhou (WZ) Badong (BD), and Zigui (ZG). C₄ plant in flooding zone was significant decreased by mean 25% compared with unflooding zone in the upstream but significantly increased the by mean 59% in the downstream. The ¹³C isotopic differences between soil and plant (Δδ¹³C) was lower than zero in both flooding and unflooding in the upstream, but was only lower than zero in flooding zone in the downstream. The proportion of C₃-derived C in soil organic carbon pool (average 74.64%) was lower for the flooding zone compared to the unflooding zone (average 87.26%) in most sites, while the proportion of C₃-derived C in LC (average 44.38%) was decreased in the flooding zone compared to the unflooding zone (69.52%) in the downstream. Additionally, the δ¹⁵N values of soil were higher than plant community in most sites, and were strongly associated with soil C and N pool content, as well as soil pH. Overall, our results revealed that soil C accumulation was primarily determined by C₃ plant in situ and new C input by existing dominant C₄ plant, whereas soil N dynamics was predictably dependent on soil relative C and N availability in response to flooding at regional scale.

Aquatic Macrophytes and Local Factors Drive Bacterial Community Distribution and Interactions in a Riparian Zone of Lake Taihu

Aquatic macrophytes rhizosphere are biogeochemical cycling hotspots in freshwater ecosystems. However, little is known regarding the effect of aquatic macrophytes on bacterial community and interactions in the riparian zones. We investigated the bacterial community composition and network structures along a gradient of the riparian zone as follows: The supralittoral and eulittoral zones with Phragmites australis, the eulittoral and infralittoral zones without P. australi. The bacterial communities in the four zones differed significantly based on taxonomic dissimilarity, but the two zones with P. australis exhibited phylogenetic closeness of the bacterial communities. The characteristics of the bacterial networks, such as connectivity, modularity, and topological roles of OTUs, were totally different between the P. australis and non-P. australis zones. Some bacterial phyla enriched in the P. australis zones were found to be putative keystone taxa in the networks, which might be involved in the regulation of bacterial interactions and plant growth. Moreover, the hydrological regime and particle size were shown to be determinants of the bacterial community and network structures in the riparian zones. In summary, our results show that the role of P. australis and local factors are crucial for constructing bacterial community and interactions in the riparian zones of lakes.