Results Of Redundancy Analysis Research Articles

A short period of revegetation and fertilization increased the nutrients, enzyme activities, and bacterial community diversity in backfill soils

The ecosystem stability of abandoned mines can be restored using vegetation restoration methods. In the present study, we aimed to investigate the variations in the physicochemical and biochemical properties of backfill soils at a quarry mining slope platform with a 1-year period of revegetation and fertilization in Anhui Province, East China. We collected backfill and native soils in different periods and analyzed their nutrients, enzyme activities, and bacterial communities. Two fertilization cycles increased the nutrients in revegetation backfill soils significantly (p < 0.05), including the available nitrogen (AN) (47.35 ± 9.40 mg/kg vs 134.23 ± 42.37 mg/kg), total phosphorus (TP) (0.38 ± 0.06 g/kg vs 0.78 ± 0.04 g/kg), available phosphorus (AP) (3.99 ± 0.84 mg/kg vs 17.23 ± 7.86 mg/kg), total potassium (TK) (14.33 ± 1.16 g/kg vs 30.74 ± 3.50 g/kg), available potassium (AK) (56.77 ± 7.33 mg/kg vs 339.26 ± 95.67 mg/kg), and soil organic matter (SOM) (13.13 ± 6.12 g/kg vs 19.60 ± 1.06 g/kg); however, the TN and SOM in revegetation and fertilization backfill soils were still much lower than those in native soils. Compared to the initial backfill soils with no revegetation, the activities of sucrase (SUC) and urease (URE) in revegetation and fertilization backfill soils increased from 2.79 ± 0.55 mg/(g·d) to 6.17 ± 3.19 mg/(g·d) and 0.12 ± 0.02 mg/(g·d) to 0.16 ± 0.02 mg/(g·d), respectively; however, they were still much lower than those in native soils. The bacterial community in backfill soils was stable during revegetation and fertilization, similar to that in native soils, with the dominant phyla being Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria. The relative abundance of Proteobacteria in backfill soils decreased from 46.12 % to 22.94 % during revegetation and fertilization, whereas those of Actinobacteria, Chloroflexi, and Acidobacteria increased from 22.2 % to 45.14 %, from 6.24 % to 15.18 %, and from 4.76 % to 24.12 %, respectively. Revegetation and fertilization improved the evenness (Simpsoneven index) and diversity (Shannon index) of bacterial community in backfill soils. The bacterial community structure in backfill soils during revegetation and fertilization approached that of the native soils. The results of redundancy analysis indicated that the bacterial communities in revegetation and fertilization backfill soils were influenced by AK, AN, SOM, URE, and SUC, whereas those in native soils were influenced by TN, SOM, and SUC. Our study indicated that only a short period of revegetation and fertilization improved physicochemical properties and enzyme activities and stabilized the structure of the bacterial community in backfill soils.

Mitigation effects and microbial mechanism of two ecological earthworms on the uptake of chlortetracycline and antibiotic resistance genes in lettuce

The contamination of greenhouse vegetable soils with antibiotics and antibiotic resistance genes (ARGs), caused by the application of livestock and poultry manure, is a prominent environmental problem. In this study, the effects of two ecological earthworms (endogeic Metaphire guillelmi and epigeic Eisenia fetida) on the accumulation and transfer of chlortetracycline (CTC) and ARGs in a soil–lettuce system were studied via pot experiments. The results revealed that earthworm application accelerated the removal of the CTC from the soil and lettuce roots and leaves, with the CTC content reducing by 11.7–22.8 %, 15.7–36.1 %, and 8.93–19.6 % compared with that of the control, respectively. Both earthworms significantly reduced the CTC uptake by lettuce roots from the soil (P < 0.05) but did not change the CTC transfer efficiency from the roots to leaves. The high-throughput quantitative PCR results showed that the relative abundance of ARGs in the soil and lettuce roots and leaves decreased by 22.4–27.0 %, 25.1–44.1 %, and 24.4–25.4 %, respectively, with the application of earthworms. Earthworm addition decreased the interspecific bacterial interactions and the relative abundance of mobile genetic elements (MGEs), which helped reduce the dissemination of ARGs. Furthermore, some indigenous soil antibiotic degraders (Pseudomonas, Flavobacterium, Sphingobium, and Microbacterium) were stimulated by the earthworms. The results of redundancy analysis indicated that the bacterial community composition, CTC residues, and MGEs were the main parameters affecting the distribution of ARGs, accounting for 91.1 % of the total distribution. In addition, the bacterial function prediction results showed that the addition of earthworms reduced the abundance of some pathogenic bacteria in the system. Overall, our findings imply that earthworm application can substantially reduce the accumulation and transmission risk of antibiotics and ARGs in soil–lettuce systems, providing a cost-effective soil bioremediation practice for addressing antibiotic and ARGs contamination to guarantee the safety of vegetables and human health.

Soil Moisture and Available Phosphorus as the Factors Driving Variation in Functional Characteristics across Different Restoration Communities in a Subtropical Mountain Ecosystem

Functional characteristics are increasingly used to evaluate the success of different vegetation restoration. Community functional diversity (FD) and the community-weighted mean (CWM), as two main complementary components, are closely linked to site environment and ecosystem functions. However, the patterns and driving factors of functional characteristics are still not clear in different vegetation restoration types. Here, four community restoration types (secondary shrubland, SL; Pinus yunnanensis forest, PF; mixed needle-broad-leaved forest, MF; natural secondary forest, NSF) were selected to investigate species diversity, FD, CWM, and soil physicochemical properties. The relative effects of species diversity and soil abiotic features on variation in functional characteristics were then evaluated. We found that different restoration communities altered most community structures and functional properties in terms of species diversity, FD, and CWM. CWM values and FD in different communities presented different distribution patterns depending on certain traits and parameters. Significant correlations between functional traits were found at the species and community scales, suggesting a potential covariation between these selected traits in communities. The results of redundancy analysis and variation partitioning showed that most of the variation in functional characteristics, especially CWM, was explained by soil moisture and available phosphorus, indicating that habitat filters regulate the functional characteristics of plant communities mainly by changing the dominant species composition and functional traits of species. Therefore, the selection of restoration species adapted to low soil moisture and available phosphorus and the construction of communities based on selected species as the dominant species can effectively drive community assembly and ecosystem functions in the vegetation restoration process.

Infiltration properties affected by slope position on cropped hillslopes

Soil infiltration properties (SIPs) and their spatial variability are essential for simulating hydrologic and erosion processes. Intensive water erosion likely leads to large spatial heterogeneity of soil particle distribution, thus the large spatial variability of general soil properties, such as SIPs. Nevertheless, little is known about the spatial variabilities of SIPs along long, gentle hillslopes and their dominant controlling factors. This study was conducted to investigate SIPs under different slope positions under agricultural management and to identify dominant SIP-related factors in the Black-soil region of Northeast China. Soil infiltration properties were determined at five slope positions (i.e. upper, middle-upper, middle, middle-lower, and lower) on two approximate 5 % hillslopes using a disc infiltrometer under three pressure heads (-3, −1.5, and 0 cm). Results showed that the initial infiltration rate (IIR), steady infiltration rate (SIR), and saturated hydraulic conductivity (KS) varied from 0.11 to 0.47 mm min−1, 0.04 to 0.30 mm min−1, and 0.04 to 0.29 mm min−1, respectively. Soil infiltration properties generally increased initially, then decreased from the upper to the lower position along the hillslope. The middle-slope position had the numeric maximum SIPs, and SIPs were significantly greater than those of the upper and lower slope positions. Compared to the middle-slope position, IIR, SIR, and Ks of the upper and lower slope positions were lower by 50.9, 61.1, 63.6 and 33.8, 32.3, 34.6 %, respectively. Initial infiltration rate, SIR, and Ks were positively correlated with sand content (r = 0.60, 0.69, 0.69; p < 0.01), total porosity (r = 0.67, 0.71, 0.71, respectively; p < 0.01), saturated soil water content (r = 0.62, 0.70, 0.71, respectively; p < 0.01), and gravel content (r = 0.48, 0.66, 0.70, respectively; p ≤ 0.01), but were negatively correlated with silt (r = -0.50, −0.49, −0.49, respectively; p ≤ 0.01) and clay (r = -0.50, −0.64, −0.63, respectively; p ≤ 0.01) contents, bulk density (r = -0.67, −0.70, −0.70, respectively; p < 0.01), and physical crust thickness (r = -0.63, −0.73, −0.73, respectively; p < 0.01) across positions of the two hillslopes. The result of redundancy analysis indicated that physical crust thickness, bulk density, and water-stable aggregate and clay contents were the dominant factors attributed to the variation in SIPs under different slope positions, and collectively they explained 74.6 % of the total variation of SIPs. Physical crust thickness alone explained the largest proportion (49.9 %) of the variation of SIPs. Results will be helpful for improving precision of hydrologic and erosion processes modeling and sustainable soil management on long, gentle hillslopes in the agricultural region of Northeast China.

Microbial response to antimony-arsenic distribution and geochemical factors at arable soil around an antimony mining site.

Antimony (Sb) mining often causes severe Sb pollution and associate arsenic (As) compound contamination. To further understand the interaction mechanism among soil microorganisms, heavy metal distribution, and geochemical factors, the effects of environmental factors on soil microbial communities under different levels of Sb-As co-contamination were studied in situ of Chashan antimony mine, Guangxi Province. The results showed that the range of Sb and As contents in soil were 1339.63-7762.28mg/kg and 2170.3-10,371.36mg/kg, respectively, and the residual fraction accounted for more than 98.0% with less than 2.0% of bioavailable fraction. Besides, the concentration of the two metals is both related to the distance to surface runoff. Different microbial communities in arable soils of each sample site were analyzed, which was significantly affected by soil environmental factors such as pH, ALN, AP, OM, Tot-Sb, Tot-As, Bio-As, and Bio-Sb. The phylum of Actinobacteria in sites 1, 4, and 5 was the most dominant and the phylum of Proteobacteria were the most dominant in sites 2 and 3. Moreover, the results of redundancy analysis (RDA), variation partition analysis (VPA), and Spearman correlation analyses demonstrated that microorganisms, heavy metal distribution, and geochemical factors interacted with each other and together shaped the microbial community. Our findings are beneficial for understanding the response of soil microorganisms to As-Sb distribution and geochemical factors in arable soils under Sb mining areas.

Dose-dependent impact of compost on rhizosphere bacterial community in heavy metal-contaminated paddy soil

Different doses (1%, 5%, 10%, mass fraction) of animal manure compost were added into a multi-heavy metal contaminated paddy soil for 150 d, and the changes in microbial structure and composition were evaluated. Compost exhibited dose-dependent effects on the rhizosphere bacterial community. Low (1%) and middle (5%) additions of compost exerted more distinct influence on bacterial community structure in rhizosphere soil than in bulk soil. The bacterial diversity after addition of compost decreased in rhizosphere soils compared with that in bulk soil. Results of redundancy analysis (RDA) indicated that different responses of rhizosphere and non-rhizosphere bacterial community to the changed soil physicochemical properties (soil pH, Pb, Cd and Cu levels) might be one reason for the differences. Thus, in agricultural management practice, the influence of compost on rhizosphere microbes should be considered.

Combined pollution of heavy metals and polycyclic aromatic hydrocarbons in the soil in Shenfu Region, China: a case of three different cities.

It is a challenging issue to investigate the combined pollution of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in urban soils. The purpose of this study was to determine the concentrations of these two pollutants in soils in Shenyang, Fushun, and Fushun New District, to analyze their distribution, their interaction, and co-contamination levels. The concentrations of heavy metals were measured by inductively coupled plasma mass spectrometry (ICP-MS), while the concentrations of 21 kinds of PAH were analyzed by gas chromatography-mass spectrometry (GC-MS). Based on the analysis of pollution concentrations and distribution patterns, the intrinsic links between heavy metals and PAHs in three different cities were assessed using a variety of multivariate analysis methods. Compared to Shenfu New District, the concentration of pollutants in Shenyang and Fushun shows a higher level. Moreover, the results of redundancy analysis (RDA) of samples may quantify the possibility of combined pollution of different heavy metal elements and PAHs. This study also affirms the important role of multivariate analysis in being used to reveal the complex interactions and spatial distribution of different pollutants.

Preparation of a new biochar-based microbial fertilizer: Nutrient release patterns and synergistic mechanisms to improve soil fertility

The contradiction between population growth and soil degradation has been increasingly prominent, such that novel fertilizers (e.g., biochar and microbial fertilizers) should be urgently developed. Biochar is a promising fertilizer carrier for microbial fertilizers due to its porous structure. However, the preparation and mechanisms of the effects of biochar-based microbial fertilizers have been rarely investigated. In this study, biochar, Bacillus, and exogenous N-P-K fertilizers served as the raw materials to prepare biochar-based microbial fertilizers (BCMFs) by optimizing the preparation methods and the process parameters. Moreover, the release patterns of N-P-K were analyzed. A pot experiment was performed on pakchoi to examine the effect of the BCMFs and explore its synergistic effect on soil fertility. The results of this study indicated that adsorption by biochar maintained bacterial activity, whereas the granulation process reduced bacterial activity. The adsorption-granulation process increased the content of total nitrogen and organic matter in the soil while enhancing the slow-release effect of the BCMFs. The Elovich model was capable of describing the nitrogen release of the BCMFs, including the diffusion and chemical processes. As indicated by the result of the column leaching experiment, the BCMFs stopped nutrient leaching more significantly than the conventional fertilizers (CF), especially in stopping N and P leaching. The use of the BCMFs improved the available soil nutrients and soil quality while enhancing the abundance of bacteria correlated with carbon and nitrogen metabolism in the soil. Moreover, a 20 % reduction in the use of the BCMFs did not significantly affect the soil available N and P and the growth status of pakchoi. The result of redundancy analysis indicated that the cation exchange capacity (CEC), NH4+-N, NO3−-N, β-glucosidase (BG), urease (URE), and alkaline phosphatase (AlkP) were the six critical environmental factors for the microbial community structure and could explain 94.8 % of the variance. The BCMFs up-regulated the levels of the above six factors, especially CEC and BG, thus improving the soil quality and enhancing the soil fertility.

Effects of Exotic and Native Earthworms on Soil Micro-Decomposers in a Subtropical Forest: A Field Mesocosm Experiment

Biological invasion is one of the most important factors affecting global biodiversity change, which can adversely affect ecosystem function. However, little is known about the effects of belowground biological invasions on soil ecosystems. In this study, we conducted a field-based mesocosm experiment to observe the effects of exotic and native earthworms (Pontoscolex corethrurus and Amynthas corticis, respectively) on soil nutrients and micro-decomposers (i.e., soil microorganisms and nematodes) in a subtropical forest in southern China. We found that exotic and native earthworms had different effects on nutrient availability and nematode communities in the soil. Specifically, exotic earthworms significantly decreased the content of nitrates in the soil and tended to decrease the total nematode abundance compared with native earthworms. Furthermore, nematode species richness and Shannon–Wiener index were lowest in the treatment with exotic earthworms and were the highest in the treatment with native earthworms. However, neither native nor exotic earthworms significantly affected soil microbial community composition. The results of redundancy analysis indicated that available phosphorus was positively correlated with nematode community. Our results demonstrated that exotic earthworms had adverse effects on the available nutrient content in the soil, and had a potential negative effect on the abundance of soil microfauna. These findings will be helpful in understanding the influence of exotic earthworms on soil micro-decomposers and the ecological consequences of earthworm invasion.

The Effects of Sampling Depth on Benthic Testate Amoeba Assemblages in Freshwater Lakes: A Case Study in Lake Valdayskoe (the East European Plain)

Testate amoebae are widely used as proxies in paleoecological reconstructions of lacustrine environments; however, our knowledge on their distribution along depth gradients are limited. This study investigates the distribution of benthic testate amoebae along a sampling depth gradient (0 to 57 m) and related environmental characteristics in Lake Valdayskoe, Russia. In total, 101 species belonging to twenty-one genera were identified. Four types of testate amoeba assemblages (littoral, sublittoral, bottom slope and profundal) were distinguished that corresponded well to the bottom zones of the lake. The results of redundancy analysis indicated that sampling depth, temperature, pH and bottom inclination significantly explained 40.2% of the total variance in the species composition. Temperature and sampling depth had the largest individual contributions of 19.2 and 7.4% (p &lt; 0.001), respectively. The minimal values of species diversity were observed on the littoral and at the lower boundary of the thermocline. We estimated depth optima and ranges for the species with high occurrences and distinguish stenobathic and eurybathic species. These data might improve the interpretations of paleoecological records of subfossil testate amoeba assemblages in lacustrine surface sediments and serve as basis for the development of a transfer function for reconstruction of lake depths.

Spatial variation in sediment connectivity of small watershed along a regional transect on the Loess Plateau

Sediment connectivity likely varies greatly over space, which further affects the processes of hydrology, erosion and sediment delivery of watershed. Small watershed is the basic geomorphologic unit for soil and water conservation. Few studies have been performed to quantify the spatial variation in sediment connectivity of small watershed at regional transect. Six typical small watersheds distributed from south to north on the Loess Plateau were selected as a regional transect to investigate the spatial variation in sediment connectivity and its influencing factors. In this study, the widely utilized index of connectivity (IC) was used to investigate the spatial variation of sediment connectivity in small watersheds. The source-sink landscape index reflecting the source or sink effect of landscape pattern on soil erosion process was utilized to compute the weights for IC. The redundancy analysis (RDA) was applied to identify the main influencing factors contributing to the spatial variation in IC. The results showed that IC increased from south to north (ranged from −2.02 to 1.76). A significant positive spatial autocorrelation was detected in IC of small watershed on the Loess Plateau (p < 0.05). The relationships between IC and environmental factors differed between different small watersheds. The results of RDA showed that the contributions of different influencing factors varied along the tested transect. The relative contributions of climate factors and vegetation factors to IC declined whereas that of land surface factors raised with latitude. Vegetation and climate were the main factors controlling the spatial variation in IC. The results are helpful to understand the spatial heterogeneity of soil erosion and evaluate the conservation benefit of vegetation restoration in semi-arid region.

Response of Gut Microbiota, Digestive Enzyme Ability, and Immune Function to Starvation in the Oriental River Prawn Macrobrachium nipponense

In order to evaluate the interplay of nutritional status and the digestive capacity, immune function, and gut microbiota in the oriental river prawn Macrobrachium nipponense, a 14-day starvation trial was conducted to detect the effects of starvation on the activities of digestive enzymes and immune enzymes and the structure of prawn gut microbiota. The adult prawns were randomly assigned to a control group (F group) and starvation group (S group) with three replicates. The F group was normally fed with commercial diet, and the S group was starved for 14 days. The result showed that digestive enzyme activities of trypsin and lipase in the hepatopancreas of the S group were significantly lower than those of the F group after 4 d of starvation ( P &lt; 0.05 ), while the activity of amylase significantly increased after 14 d of starvation ( P &lt; 0.05 ). Moreover, the results of the histological analysis of prawn gut showed that both the height of epithelial cells and microvilli of intestine in the S group were obviously decreased than those in the F group ( P &lt; 0.05 ) after 14 d of starvation. The activities of immune-related enzymes including superoxide dismutase, catalase, and acid phosphatase in the hepatopancreas of the S group significantly decreased after 4 d of starvation, and lysozyme activity of the F group was lower than that of the S group after 7 d of starvation ( P &lt; 0.05 ). In addition, the results of Illumina high-throughput sequencing showed that a total of 14,285 OTUs were obtained and classified into 30 phyla, among which Actinobacteria and Proteobacteria were the predominant microflora in the intestinal microbial communities of both groups. However, the relative abundance of opportunistic pathogens was significantly increased in the S group, while the relative abundance of beneficial bacterium was decreased ( P &lt; 0.05 ). The bacterial richness with the Chao estimator was significantly higher in the F group than in the S group ( P &lt; 0.05 ). Both the results of principal coordinate analysis (PCoA) and nonmetric multidimensional scaling (NMDS) demonstrated that the intestinal microbiota of the F group was separate from those of the S group. The result of functional prediction of the metabolic pathways showed that the intestinal microbiota was enriched in the KEGG pathways of amino acid, carbohydrate, fatty acid, and lipid biosynthesis and degradation at level 2. This result implied that the microbiota of shrimp gut decreased nutrition metabolism under the stress of starvation. Meanwhile, comparing to the F group, the immune-related pathway of enterobacterial common antigen biosynthesis was markedly reduced in the S group ( P &lt; 0.05 ). The result of redundancy analysis (RDA) further confirmed that the activities of digestive and immune enzymes were correlated with the microbial community structure. Finally, the structural equation modeling highlighted that changes in the activities of digestive and immune enzymes were directly related to the gut bacterial community and notably affected prawn growth.

Water Availability, Soil Characteristics, and Confounding Effects on the Patterns of Biocrust Diversity in the Desert Regions of Northern China.

The species diversity of biocrusts is an important community characteristic in determining their multiple ecosystem functions. Hence, understanding the diversity patterns of biocrusts and their environmental drivers is of fundamental importance. However, explain variables often correlated with each other; thus, the confounding effects among them may arise and result in spurious causal relationships and biased ecological inferences. In this study, we investigated the richness of three biocrust-forming components (mosses, lichens, and cyanobacteria–algae) and their environmental variables across six desert regions of northern China. A comparison between conventional redundancy analysis (RDA) and structural equation model (SEM) was conducted to study the environmental driver-richness relationship and the confounding effects. Our results showed that three latent variables related to water availability, soil texture, and soil salinity and sodicity, could account for the main environmental variations and explain the diversity patterns of biocrusts at the intracontinental scale. Water availability was positively and negatively related to the richness of mosses and cyanobacteria–algae, respectively, while soil texture was positively related to the richness of lichens. In addition, environmental variables confounded with each other caused distinct driver-richness relationships between results of RDA and SEM. Therefore, we suggest that future multivariable studies should utilize path analysis in conjunction with conventional canonical ordination to facilitate more rigorous ecological inferences.

Reliability and accuracy analysis of time-weighted average exposure to heavy metals based on personal exposure

Time-weighted average (TWA) exposure has been used as a surrogate for personal air exposure in some large-scale studies. However, the uncertainties of TWA exposure remain to be determined, although its boundedness has been widely recognized. This study aims to evaluate the reliability and accuracy of TWA exposure based on personal exposure. A total of 180 combined indoor-outdoor-personal air samples were collected of six cities during the non-heating and heating periods. The personal exposure levels of Hg, As, Cd, and Pb were 0.16, 21.20, 0.74, and 34.47 ng/m3 in the non-heating period, respectively, but were 0.20, 34.53, 3.45, and 18.59 ng/m3 in the heating period, respectively. The ratios of TWA and personal exposure of heavy metal(loid)s ranged from 0.91 to 1.53. Indoor pollution was the most significant factor of TWA exposure, accounting for 78.3–97.6% and 88.4–98.6% in the heating and non-heating period, respectively. Based on the results of redundancy analysis and risk assessment by TWA exposure, we concluded that TWA exposure could be used for qualitative investigation, as a substitute for personal exposure, but it may result in large bias when used for quantitative investigation. Larger sample size and more exposure scenarios can reduce the estimation error of TWA.

Main drivers of plant diversity patterns of rubber plantations in the Greater Mekong Subregion

Abstract. The Greater Mekong Subregion (GMS) is one the global biodiversity hotspots. However, the diversity has been seriously threatened due to environmental degradation and deforestation, especially by expansion of rubber plantations. Yet, little is known about the impact of expansion of rubber plantations on regional plant diversity as well as the drivers for plant diversity of rubber plantations in this region. In this study, we analyzed plant diversity patterns of rubber plantations in the GMS based on a ground survey of a large number of samples. We found that diversity varied across countries due to varying agricultural intensities. Laos had the highest diversity, followed China, Myanmar, and Cambodia. Plant species richness of Laos was about 1.5 times that of Vietnam. We uncovered latitudinal gradients in plant diversity across these artificial forests of rubber plantations and these gradients caused by environmental variables such as temperature. Results of redundancy analysis (RDA), multiple regression, and random forest demonstrated that latitude and temperature were the two most important drivers for the composition and diversity of rubber plantations in the GMS. Meanwhile, we also found that higher dominance of some exotic species (such as Chromolaena odorata and Mimosa pudica) was associated with a loss of plant diversity within rubber plantations; however, not all exotic plants cause the loss of plant diversity in rubber plantations. In conclusion, not only environmental factors (temperature), but also exotic species were the main factors affecting plant diversity of these artificial stands. Much more effort should be made to balance agricultural production with conservation goals in this region, particularly to minimize the diversity loss in Vietnam and Cambodia.

Phylogenetic Structure of Synechococcus Assemblages and Its Environmental Determinants in the Bay and Strait Areas of a Continental Sea.

Marine Synechococcus, a significant contributor to primary production, shows high phylogenetic diversity. However, studies on its phylogenetic composition in the Bohai Sea, the largest continental sea in China, are lacking. We sequenced rpoC1 (encodes the RNA polymerase β’ subunit protein) in samples from the Laizhou Bay (LZB) and Bohai Strait (BS) in June and November using high-throughput sequencing to reveal the phylogenetic composition of Synechococcus assemblages in the bay and strait areas of the Bohai Sea. In total, 12 lineages representing Synechococcus subclusters S5.1, S5.2, and S5.3 were identified. Spatially, clade I was obligately dominant in BS. In contrast, the Synechococcus assemblage in LZB was more diverse, with clades VI and III being highly abundant. In addition, we detected strong variation in Synechococcus structure between June and November in the Bohai Sea. Clades II, III, XX, and miyav were only detected in November. Vertically, variation in Synechococcus assemblage was not apparent among the water layers probably due to the shallow water depth with intense water mixing. Results of redundancy analysis (RDA) and random forest (RF) analysis together highlighted the key role of silicate in the Synechococcus assemblage. Our results suggested that the Bohai Sea provides various niches for different Synechococcus clades, resulting in a special phylogenetic composition of the Synechococcus assemblage, compared with that in the adjacent shelf sea and other continental seas in the world.

Land use driven change in soil organic carbon affects soil microbial community assembly in the riparian of Three Gorges Reservoir Region

After decades of anti-seasonal water fluctuation in the Three Gorges Reservoir (TGR), a distinctive riparian zone had been formed and played critical roles on soil biogeochemistry cycling, substance exchange and soil microbial functions. However, the effect of land use on terrestrial ecological processes and soil microbial community assembly in riparian zone was still imprecise. This study focused on the relationship of soil properties and microbial communities in paddy and dryland soils of a typical riparian zone in the TGR. The results indicated a higher level of accumulation of total organic carbon (TOC) in paddy soil (14.88–20.29 g kg−1) than that in dryland soil (7.59–16.20 g kg−1). The riparian soil was slightly polluted by cadmium and phthalate acid esters with an average concentration of 0.19 mg kg−1 and 6.45 mg kg−1, which may be from agricultural sources, posing a potential health risk. Based on 16S rRNA sequencing analysis, there was a higher microbial diversity in paddy soils than dryland soils, and Acidobacteriaceae and Anaerolineaceae represented the dominant taxa in dryland and paddy soils, respectively. Furthermore, the results of redundancy analysis and structural equation modeling showed that land use driven change in soil organic carbon affected the fate of soil pollutants, and constructed soil microbial communities in the riparian zone of TGR. Null model revealed that homogeneous selection explained about 76.36% and 53.33% microbial community assembly, followed by dispersal limitation (14.54% and 37.50%) in dryland and paddy soil. In consequence, a strong effect of environmental filtering was observed on arable soil microbial community structure with different land use in the riparian zone of TGR, and TOC was the key regulator.

Community Structure of Eukaryotic Phytoplankton in Wetland of Golmud River and Its Lower Reaches and Relative Environmental Factors

Identification of the community structure of phytoplankton is an important link in studying the structure and function of aquatic ecosystems. However, research on the community structure of phytoplankton in the Golmud area is very scarce at present. To explore the composition of phytoplankton in the Golmud area, eukaryotic phytoplankton and environmental parameters were sampled in September 2020. The composition and diversity of the eukaryotic phytoplankton community were determined by microscopic observation and Illumina high-throughput sequencing technology. The results showed that a total of 40 species of eukaryotic phytoplankton from 4 phyla were identified by microscopic observation, and 154 species of eukaryotic phytoplankton from 7 phyla were obtained by high-throughput sequencing, mainly Bacillariophyta and Chlorophyta. The dominant species were Dunaliella sp., Teleaulax sp., Parvodinium mixtum, and Lindavia radiosa. The eukaryotic phytoplankton density in summer was 0.09–12.08 × 105 cells/L, the total biomass was 0.002–0.55 mg/L, and the concentration of chlorophyll-a was 0.00–0.91 μg/L. Multiple α diversity indices showed that the diversity of water in different salinities was in the order of freshwater &gt; brackish &gt; saline. The β diversity results showed that the eukaryotic phytoplankton community composition was more similar in water with the same salinity. The redundancy analysis results of water with different salinities showed that environmental factors susc as salinity, total phosphorus concentration, and dissolved oxygen affected the eukaryotic phytoplankton community structure, among which salinity had the greatest influence.

Responses of N2O Production and Abundances of Associated Microorganisms to Soil Profiles and Water Regime in Two Paddy Soils

Soil moisture is one of the critical factors affecting N2O emissions. The water regime affects the physical and chemical properties of paddy soil in different soil layers, which, in turn, affects N2O emissions and microbial growth. However, there are few reports on the effects of different soil layers and soil moisture conditions on N2O emission characteristics and microbial mechanisms. A 21-day microcosm experiment was performed to research the effects of soil moisture levels (60%, 100%, and 200% water holding capacity, WHC) and different soil layers (0–10, 10–20, and 20–40 cm) on N2O emissions in hydromorphic and gleyed paddy soils. Function microbes involved in nitrification and denitrification were determined by quantitative PCR. Moreover, the abiotic variables pH, Eh, and exchangeable Fe2+, Fe3+, NH4+-N, and NO3−-N were also analyzed. Results showed that N2O emissions of gleyed paddy soil were significantly higher than that of hydromorphic paddy soil, which was consistent with the result of the abundance of nitrifier and denitrifier in the two paddy soils. Soil depth, water content, and their interaction significantly affected N2O emission (p &lt; 0.05). Cumulative emissions of N2O from each layer of the two paddy soils at 100% and 200% WHC were significantly higher than that under 60% WHC (p &lt; 0.05). N2O emissions decreased significantly with the increase of soil depth (p &lt; 0.05), which was consistent with the change in the abundance of soil nitrifier (AOB and AOA) and denitrifier (nirK and nosZ) function genes with soil depth. The abundance of AOB, AOA, and nirK and nosZ genes decreased significantly with soil depth (p &lt; 0.05), but did not respond significantly to the water regime. Based on the results of redundancy analysis, the contents of Fe2+ and Fe3+ were positively correlated with N2O emissions and the abundance of AOB, AOA, and nirK and nosZ genes. These results indicate that N2O emissions and the abundance of associated microbes are selectively affected by soil moisture and soil layers in the two paddy soils.

Rhizosphere enzyme activities and microorganisms drive the transformation of organic and inorganic carbon in saline\u2013alkali soil region

Western Jilin Province is one of the world's three major saline–alkali land distribution areas, and is also an important area of global climate change and carbon cycle research. Rhizosphere soil microorganisms and enzymes are the most active components in soil, which are closely related to soil carbon cycle and can reflect soil organic carbon (SOC) dynamics sensitively. Soil inorganic carbon (SIC) is the main existing form of soil carbon pool in arid saline–alkali land, and its quantity distribution affects the pattern of soil carbon accumulation and storage. Previous studies mostly focus on SOC, and pay little attention to SIC. Illumina Miseq high-throughput sequencing technology was used to reveal the changes of community structure in three maize fields (M1, M2 and M3) and three rice fields (R1, R2 and R3), which were affected by different levels of salinization during soil development. It is a new research topic of soil carbon cycle in saline–alkali soil region to investigate the effects of soil microorganisms and soil enzymes on the transformation of SOC and SIC in the rhizosphere. The results showed that the root—soil—microorganism interaction was changed by saline–alkali stress. The activities of catalase, invertase, amylase and β-glucosidase decreased with increasing salinity. At the phylum level, most bacterial abundance decreases with increasing salinity. However, the relative abundance of Proteobacteria and Firmicutes in maize field and Firmicutes, Proteobacteria and Nitrospirae in rice field increased sharply under saline–alkali stress. The results of redundancy analysis showed that the differences of rhizosphere soil between the three maize and three rice fields were mainly affected by ESP, pH and soil salt content. In saline–alkali soil region, β-glucosidase activity and amylase were significantly positively correlated with SOC content in maize fields, while catalase and β-glucosidase were significantly positively correlated with SOC content in rice fields. Actinobacteria, Bacteroidetes and Verrucomicrobia had significant positive effects on SOC content of maize and rice fields. Proteobacteria, Gemmatimonadetes and Nitrospirae were positively correlated with SIC content. These enzymes and microorganisms are beneficial to soil carbon sequestration in saline–alkali soils.