Stable Community Structure Research Articles

Species composition and community structure of warm temperate deciduous broadleaved forests in Huangguan of Qinling Mountains, China

The Qinling Mountain is a natural boundary between warm temperate zone and subtropical zone. While the China Forest Biodiversity Monitoring Network (CForBio) have basically covered most of the climate regions in China, few plots were located in the climate transition zone. Following the field protocol of CForBio and the Center for Tropical Forest Science (CTFS), a 25 hm2(500 m×500 m) forest plot was established in Huangguan Nature Reserve in Shaanxi Province, China, in 2019. In this study, we analyzed species composition, flora characteristics, diameter class structure, and spatial distribution patterns of dominant tree species based on the data of all woody species with a diameter at breast height (DBH) ≥1 cm. The results showed that there were 75137 woody individuals with DBH ≥1 cm in the plot (95679 when including branching individuals), belonging to 121 species, 83 genera and 44 families. The flora type at the genera level was mainly temperate, accounting for 71.1% of the total genera, and mixed with some tropical components. The dominant species in the community were obvious, with the number of individuals in the top 5 species exceeding 40% of the total number of individuals, the number of individuals in the top 50 species accounting for 95% of the total number of individuals, and the number of individuals in the remaining 61 species being less than 5% of the total. The diameter distribution of all woody indivi-duals in the plot was inverted 'J' type. Spatial distribution patterns varied across the four most abundant species with importance value >5. The degree of aggregation within species decreased with the increases of scales, while the spatial distribution of different species was affected by environmental heterogeneity. Warm-temperate deciduous broadleaved forest in Qinling Mountains had abundant species, stable community structure and good regeneration, reflecting the typical characteristics of the transition from warm temperate zone to subtropical zone. Environmental heterogeneity might be an important factor affecting the spatial distribution of tree species in the plot.

Volcanism-induced late Boda warming in the Late Ordovician: Evidence from the Upper Yangtze Platform, South China

Late Boda warming was the last warm episode in the Late Ordovician, and little is known about its cause. Volcanism was a hypothetical candidate that triggered this warming event owing to its potential to enhance the atmospheric CO2 level. Here, we conducted a high-resolution petrographic and geochemical study on the bentonite beds-bearing intervals from the Upper Ordovician Wufeng Formation in South China. This investigation enables us to find the detailed process of paleoenvironmental repercussions induced by volcanism from both short-term and long-term perspectives. The short-term effect was revealed by a 25-cm-long drill core bracketing three cycles of volcanic activity. Three nearly identical cycles have been identified, and each cycle is comprised of a bentonite bed, a siliceous clay-rich mudstone interval, a radiolarian bed, and a siliceous mudstone interval with intercalations of thin pyrite layer. During the eruption stage, a series of environmental and biogeochemical disruptions were brought to the local system, including ocean fertilization, the elevation of paleoproductivity, the onset of euxinia/intensified ocean anoxia, a warmer climate, and enhanced weathering. With the waning of volcanic activities, the volcanic impacts weakened, and a relatively stable water-column chemistry, microbial populations, diversity, and community structure were established until the onset of the subsequent volcanic event that broke equilibrium. The long-term effect was illustrated by the correlation between the distribution of bentonite beds and coeval global sea-level fluctuations. Our results show that intense and frequent volcanic activities in South China, probably contributed by coeval volcanic activities from other regions worldwide, exerted a cumulative heating effect on the global system, contributing to late Boda warming.

Community structures of bacteria and archaea associated with the biodeterioration of sandstone sculptures at the Beishiku Temple

The Beishiku (North Grottoes) Temple is suffering from serious weathering erosion as well as biological attacks. In this study, the total genomic DNA of 72 samples was extracted to elucidate the communities and distribution of both bacteria and archaea in biodeteriorated and weathered sandstone materials using a high-throughput sequencing analysis. As a result, the predominant bacterial communities belonged to the genera Deinococcus, Thermus, Pseudomonas, Rubrobacter, and Chroococcidiopsis. Interestingly, archaea (particularly the Candidatus Nitrocosmicus genus) with a putative ammonia-oxidizing function were dominant in the biodeteriorated samples where halophilic archaeal groups (particularly Halalkalicoccus and Halococcus genera) were also enriched. Moreover, the CCA showed that the distribution of microbial communities was mainly driven by the sunlight intensity, moisture, soluble salts and pH. In addition, a co-occurrence network analysis indicated that a more complex and stable community structure existed in the outside surface samples. The ecological functions of these community members were mainly predicted to be associated with chemoheterotrophy, phototrophy and aerobic ammonia oxidation, which maintained the common survival of biodeteriogens on stone heritage. Our findings unveil the distribution patterns of bacteria and archaea on sandstone sculptures in the subhumid climate, highlight the key factors affecting these patterns, and thus provide a reference basis for mitigation management and policies to prevent biodeterioration and protect such cultural heritages.

Research advances of microbial denitrification and application in black and odorous water

High nitrogen content is considered to be one of the main reasons for the black and odor phenomenon in rivers. Microbial denitrification has been widely concerned because of its simple operation, high economic efficiency, short repair time and little impact on the surrounding environment. However, its denitrification process is also affected by environmental factors, pollutants and changes in microbial communities. In this paper, the main bacterium participating in sewage treatment of nitrification, denitrification and anaerobic ammonia oxidation were introduced, and then the adaptation situation and distribution of microbial community in each denitrification process were summarized. Finally, applications and prospects were objectively provided by microbial agents, constructed wetlands and ecological floating islands. According to the existing research results, it is believed that microbial remediation has a broad prospect in the treatment of urban black and odorous water bodies. However, it is difficult to maintain a stable bacterial community structure, denitrification activity and environmental adaptability of microbial remediation technology in river channels, which is the bottleneck of its application in the treatment of black and odorous water.

KERAGAMAN KELINCI LAUT (NUDIBRANCHIA) DI PERAIRAN LAUT SULAWESI UTARA

This study aims to 1) identify the species of Nudibranchia in North Sulawesi marine waters, especially in Malalayang waters, Teep waters, Sangihe waters, Bunaken waters, Gangga waters and Lembeh straits, 2) find out species of Nudibranchia that is found in all sites, and 3) find out index community structure of Nudibranchia in all sites. The result show that there were 11 species of Nudibranchia in Malalayang waters, 27 species in Lembeh Strait, 11 species in Teep waters, 57 species in Bunaken waters, 91 species in Bangka waters, and 20 species in Sangihe waters. Up to now, there were 139 species of Nudibranchia in North Sulawesi marine waters, where Species of Phyllidiella pustulosa, Phyllidia ocellata, Phyllidia varicose, Chromodoris annae, and Glossodoris cincta were found in all study locations. The species of Doriprismatica atromarginata was only found in the Malalayang waters. A high Index Diversity was found in Bunaken and Bangka waters, and a middle Index Diversity was found in the waters of Lembeh Strait, Teep, and Sangihe. A stable community structure was found for all locations, while a low domination was categorized to all locations. Keywords: Nudibranchia, species, diversity, evenness, domination, and community structure.

Impacts of straw returning and N application on NH4+-N loss, microbially reducible Fe(III) and bacterial community composition in saline-alkaline paddy soils

Soil nitrogen deficiency and poor fertility have been widely concerned in saline-alkaline paddy soil of the Yellow River Delta (YRD). NH4+-N content regulated by soil organic carbon (SOC) and the rate of feammox reaction which provides a worth understanding in nitrogen (N) transformation. A 5-year field experiment was carried out to investigate the effect of straw returning and N fertilization rates on the NH4+-N, microbially reducible Fe(III) (MR-Fe) and bacterial community composition in YRD. Six treatments were designed, including three straw returning rates (S0, S1 and S2, which was 0, 4500 and 9000 kg C ha−1, respectively) under two N fertilization levels (N1 and N2, which was 400 and 255 kg N ha−1, respectively). Our results showed that, compared with N1 level, soil NH4+-N content showed no significant changes in N2 level at same straw returning rate. Under N2 level, compared with S0 and S2 rates, NH4+-N content was increased by 64.8% and 50.3% in S1 rate, respectively. SOC content showed no difference between S1 and S2 treatments, which were higher than that in S0 treatment. While the labile carbon (i.e., readily oxidized organic carbon and dissolved organic carbon) was increased in S2 treatment, which promoted the dissolution of MR-Fe and increased the relative abundance of Geobacter and Anaeromyxobacter. Additionally, the structural equation models further indicated that more soil labile carbon could improve MR-Fe content and Geobacter and Anaeromyxobacter abundance, which decreased soil NH4+-N content via feammox reaction. Therefore, half straw returning with the optimized N fertilization decreased NH4+ oxidation and Fe reduction by supporting a more stable bacteria community structure, which played a key role in N availability and promoted the sustainable development of modern agriculture in saline-alkaline paddy soils.

Evolution of social relationships between first-year students at middle school: from cliques to circles

People organize their social relationships under a restriction on the number that a single individual can maintain simultaneously (the so-called Dunbar’s number, ~150). Additionally, personal networks show a characteristic layered structure where each layer corresponds to relationships of different emotional closeness. This structure, referred to as Dunbar’s circles, has mostly been considered from a static viewpoint, and their structure and evolution is largely unexplored. Here we study the issue of the evolution of the structure of positive and negative relationships in early adolescence by using data from students in their first year at middle school obtained from surveys conducted in class in two different waves separated by several months. Our results show that, initially, students have a lower number of total relationships but the majority are more intense and over time they report a higher number of total relationships, but the more intense relationships appear in a lower proportion. We have also found differences in the structure of communities at both temporal moments. While in the first instance the communities that appeared are mixed, made up of both boys and girls, in the second they changed so that they were separated primarily by gender. In addition, the size of each community was stabilized around 15 people, which coincides with the size of the second Dunbar’s circle, known as the sympathy group in social psychology. As a consequence, in groups with around 20 students of the same gender, they tend to split in two separate communities of about 10 each, below the second Dunbar’s circle threshold. On the other hand, groups with more stable community structure appear to go through the inverse process of friendship evolution, becoming more focused on their best relationships. All these results suggest how the layered structure of the personal network, as well as the community structure of the social network, emerge directly from the union of both positive and negative relationships. Thus, we provide a new perspective about its temporal evolution that may have relevant applications to improve school life and student performance.

Picophytoplankton identification by flow cytometry and high-throughput sequencing in a clean reservoir

Understanding picophytoplankton variations that play important roles in the material circulation and energy flow are critical to assessing overall status of waterbody, especially for clean reservoirs which remain a relatively stable community structure and high species diversity due to lower nitrogen and phosphorus nutrients. However, their response to key environmental factors and tightly acting microbial remains poorly understood. Traditional quantification methods are limited, such as chlorophyll-a, turbidity and microscope. There are still many defects with present molecular analysis. In this study, a flow cytometric analysis and high-throughput sequencing combination methodology was developed and tested on clean water from a reservoir, by a monthly dynamic for a vegetative period April-September in 2019 to improve the accuracy of dynamic monitoring for the picophytoplankton system. More species of Pico-Cyanobacteria and Pico-Eukaryotes were discovered. The increased percentage of pigment compounds from 8.2% to 76.3% proves the effective reduce of heterotrophic disturbing and enrichment of target populations. Picophytoplankton that was previously neglected due to their low relative abundance has once again entered the scope of our eyes. Phytoplankton were divided into three categories. The first one was the highly abundant and frequently present taxa, the second one was the low-abundance but highly-transient population, and the third one was the low abundance and stable group. Synechococcus, Emiliania, Tetraselmis and Thalassiosira were dominant picophytoplankton and displayed obvious temporal and spatial distribution characteristics. Pico-PE rich Cyanobacteria and Nano-Eukaryotes with high transience abnormally increased in summer. Temperature, ammonia-N, nitrate-N, turbidity and total nitrogen were most influencing factors, while some picophytoplankton with special physiological structure showed distinct competitive advantages in the microbial community. As for the off-flavor compounds, the concentration of 2-methylisoborneol and geosmin were high even 66.7% and 20.8% of the samples exceeded their olfactory threshold. Chrysochromuina, Planktothrix and Microcystis might be the potential producers.

Long-term in situ bioelectrochemical monitoring of biohythane process: Metabolic interactions and microbial evolution

Microbial stability and evolution are a critical aspect for biosensors, especially in detecting dynamic and emerging anaerobic biohythane production. In this study, two upflow air–cathode chamber microbial fuel cells (UMFCs) were developed for in situ monitoring of the biohydrogen and biomethane reactors under a COD range of 1000–6000 mg/L and 150–1000 mg/L, respectively. Illumina MiSeq sequencing evidenced the dramatic shift of dominant microbial communities in UMFCs from hydrolytic and acidification bacteria (Clostridiaceae_1, Ruminococcaceae, Peptostreptococcaceae) to acetate-oxidizing bacteria (Synergistaceae, Dysgonomonadaceae, Spirochaetaceae). In addition, exoelectroactive bacteria evaluated from Enterobacteriaceae and Burkholderiaceae to Desulfovibrionaceae and Propionibacteriaceae. Especially, Hydrogenotrophic methanogens (Methanobacteriaceae) were abundant at 93.41% in UMFC (for monitoring hydrogen reactor), which was speculated to be a major metabolic pathway for methane production. Principal component analysis revealed a similarity in microbial structure between UMFCs and methane bioreactors. Microbial network analysis suggested a more stable community structure of UMFCs with 205 days’ operation.

The temporal dynamics of bacteria in the coelomic fluid of sea cucumber Apostichopus japonicus after evisceration

Sea cucumbers have been emerged as important models to study organ regeneration and development owing to the capacity to regenerate its organs quickly after evisceration. Evisceration is a special defense mechanism for sea cucumber to eject all of internal organs when they encounter predators or adverse environmental conditions. However, little was known about the dynamics of bacterial community in coelomic fluid after evisceration. In the present study, evisceration was induced by intracelomic injection of 0.35 M KCl, and the significantly alternation of bacterial community in coelomic fluid of sea cucumber Apostichopus japonicus was observed with lower diversity and total bacterial load at 7 dpe (days post evisceration) and 14 dpe. The bacterial community was tended to restore at 28 dpe. In particular, relative abundances of Bacteroidetes and Rubritaleaceae, which involved in degradation of polysaccharides and lipid, increased significantly at 7 dpe (p < 0.05), and returned to the original level at 28 dpe. In addition, the predicted functions of bacterial community indicated that the bacteria associated with metabolism pathways of amino acid, lipid and carbohydrate also increased significantly at 7 dpe. These results suggested that the bacterial community in coelomic fluid of A. japonicus was highly dynamic and could rebuild a stable community structure after evisceration. It was suggested that the enriched metabolic related beneficial bacteria at early stage played a role after evisceration in terms of decomposing polysaccharides and lipid to provide energy.

Priority effects dictate community structure and alter virulence of fungal-bacterial biofilms

Polymicrobial biofilms are a hallmark of chronic wound infection. The forces governing assembly and maturation of these microbial ecosystems are largely unexplored but the consequences on host response and clinical outcome can be significant. In the context of wound healing, formation of a biofilm and a stable microbial community structure is associated with impaired tissue repair resulting in a non-healing chronic wound. These types of wounds can persist for years simmering below the threshold of classically defined clinical infection (which includes heat, pain, redness, and swelling) and cycling through phases of recurrent infection. In the most severe outcome, amputation of lower extremities may occur if spreading infection ensues. Here we take an ecological perspective to study priority effects and competitive exclusion on overall biofilm community structure in a three-membered community comprised of strains of Staphylococcus aureus, Citrobacter freundii, and Candida albicans derived from a chronic wound. We show that both priority effects and inter-bacterial competition for binding to C. albicans biofilms significantly shape community structure on both abiotic and biotic substrates, such as ex vivo human skin wounds. We further show attachment of C. freundii to C. albicans is mediated by mannose-binding lectins. Co-cultures of C. freundii and C. albicans trigger the yeast-to-hyphae transition, resulting in a significant increase in neutrophil death and inflammation compared to either species alone. Collectively, the results presented here facilitate our understanding of fungal-bacterial interactions and their effects on host-microbe interactions, pathogenesis, and ultimately, wound healing.

Microbial analysis for the ammonium removal from landfill leachate in an aerobic granular sludge sequencing batch reactor

In this study, a laboratory-scale sequencing batch reactor (SBR) equipped with aerobic granular sludge (AGS) technology was continuously operated for 220 days to remove ammonium from an existing landfill leachate. The ammonium removal was characterized by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) technology. This method helped to analyze the long-term community structural stability of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and denitrifying bacteria (DB) throughout the experiment. Simultaneously, 16S rRNA gene cloning and sequencing analysis identified the dominant species of different microbial species. Experimental results confirmed that ammonium removal was inhibited at the high nitrogen loading rate (NLR) stage while the low NLR stage achieved satisfactory ammonium removal. Moreover, the findings demonstrated that functionally stable wastewater treatment bioreactors facilitated the occurrence of stable microbial community structures.

Soil water content as a critical factor for stable bacterial community structure and degradative activity in maritime Antarctic soil.

Recent increases in air temperature across the Antarctic Peninsula may prolong the thawing period and directly affect the soil temperature (Ts) and volumetric soil water content (SWC) in maritime tundra. Under an 8°C soil warming scenario, two customized microcosm systems with maritime Antarctic soils were incubated to investigate the differential influence of SWC on the bacterial community and degradation activity of humic substances (HS), the largest constituent of soil organic carbon and a key component of the terrestrial ecosystem. When the microcosm soil (KS1-4Feb) was incubated for 90 days (T = 90) at a constant SWC of ~32%, the initial HS content (167.0 mg/g of dried soil) decreased to 156.0 mg (approximately 6.6% loss, p < 0.05). However, when another microcosm soil (KS1-4Apr) was incubated with SWCs that gradually decreased from 37% to 9% for T = 90, HS degradation was undetected. The low HS degradative activity persisted, even after the SWC was restored to 30% with water supply for an additional T = 30. Overall bacterial community structure remained relatively stable at a constant SWC setting (KS1-4Feb). In contrast, we saw marked shifts in the bacterial community structure with the changing SWC regimen (KS1-4Apr), suggesting that the soil bacterial communities are vulnerable to drying and re-wetting conditions. These microcosm experiments provide new information regarding the effects of constant SWC and higher Ts on bacterial communities for HS degradation in maritime Antarctic tundra soil.

A spatiotemporal dynamic analyses approach for dockless bike-share system

The landscape of cycling activities from a dockless bike-share system is dynamic over space and time. Decoding usage patterns from bike-share trips have been a highly charged area in the literature. Therefore, this study aims at developing an analytical approach to understanding the trip demands of bike-share and model the spatiotemporal dynamics of cycling flows. Under the proposed framework, global and local Moran's I indexes measure the spatial autocorrelation of cycling trips in different traffic zones, and community detection extracts the network structure of bike traffic. The developed approach is subsequently applied to the dockless bike-share system in Singapore. It is found that the spatial distribution of the cycling trips shows significant clustering pattern. Specifically, the global Moran's indexes of weekdays are larger than that of the weekends in the same time span and, moreover, the global Moran's indexes of peak hours are smaller than the off-peak hours on the same day. Several hotspots with the top high local Moran's I values are detected, which keep relatively stable during different times of the day on both weekdays and weekends. We also found that there existed a stable community structure of bike-share trips. In contrast, the average sizes of the top 15 communities on a weekday were statistically higher than those on the weekend, at a significance level of 0.01. The proposed modeling framework provides practice insights to bike fleet management, cycling path design, and other urban and transportation planning practices.

Long-range phase synchronization of high-frequency oscillations in human cortex

Inter-areal synchronization of neuronal oscillations at frequencies below ~100 Hz is a pervasive feature of neuronal activity and is thought to regulate communication in neuronal circuits. In contrast, faster activities and oscillations have been considered to be largely local-circuit-level phenomena without large-scale synchronization between brain regions. We show, using human intracerebral recordings, that 100–400 Hz high-frequency oscillations (HFOs) may be synchronized between widely distributed brain regions. HFO synchronization expresses individual frequency peaks and exhibits reliable connectivity patterns that show stable community structuring. HFO synchronization is also characterized by a laminar profile opposite to that of lower frequencies. Importantly, HFO synchronization is both transiently enhanced and suppressed in separate frequency bands during a response-inhibition task. These findings show that HFO synchronization constitutes a functionally significant form of neuronal spike-timing relationships in brain activity and thus a mesoscopic indication of neuronal communication per se.

Hydrogen production performance from food waste using piggery anaerobic digested residues inoculum in long-term systems

The objective of this study was to investigate the hydrogen production performance from food waste using piggery anaerobic digested residues (PADRs) inoculum. Multiple parameters were evaluated such as organic load rate (OLR), pH, and hydraulic retention time (HRT), over a wide range of values in long-term dark fermentation systems. Results showed that a value of 126.50 mL/gVS·d hydrogen yield was achieved at OLR 6 g VS/L·d under thermophilic condition. A relatively stable structural composition dominated by Thermoanaerobacterium was maintained even suffering from OLR and acid shock. On the contrary, mesophilic fermentation performed acetic acids accumulation and an average hydrogen yield of less than 80 mL/gVS·d. High OLR and low pH (range of 5.0–5.5) led to the establishment of Lactobacillus. Beyond this range, the relative abundance of Olsenella, Streptococcus, and other bacteria showed a significant difference under different operating conditions, which caused weak resistance to external shocks during mesophilic fermentation. It showed that PADRs was capable of obtaining optimal hydrogen production performance under thermophilic condition from food waste with a stable microbial community structure.

Impact of hydraulic retention time on swine wastewater treatment by aerobic granular sludge sequencing batch reactor.

In this study, the effect of hydraulic retention time (HRT) on the performance of aerobic granular sludge (AGS) treating swine wastewater (SW) in sequencing batch reactor (SBR) was investigated. The HRT was set at 4.8, 6, 8, 12, and 16 h and performed in five parallel aerobic granular sludge sequence batch reactors (AGSBRs), respectively. The results showed that sedimentation performance and biomass concentration were improved by decreasing the HRT from 16 to 8 h. However, when further decreasing HRT from 8 to 4.8 h, the AGS performance became worse. The AGS process with HRT of 8 h exhibited high pollutant removal efficiency, and an abundant microbial community and a stable microbial community structure were observed. High-throughput 16S rRNA analysis revealed that there were significant differences between the microorganisms in AGS samples with HRT of 8 h at the phylum level and that the dominant microbes changed as the process proceeded. At the genus level, the species and relative abundance of microorganisms gradually evolved for AGS stability in all cases.

Revealing the strong and stable community structure in social networks

In a complex network, the global similarity standard is of high complexity and local similarity standard has biased error on node similarity. This paper puts forward a community discovering algorithm OBS, based on the degree of contribution of shared nodes in complex network. It distributes the contribution, using the degree of shared nodes as the unit, equally, which is made by shared nodes. Compared with average commute time standard, Random Walk with Restart standard and Hierarchical Structure Method standard, OBS standard has a more veracious forecast to the similar relationship between nodes. The experimental results of artificial network and typical complex network show that OBS algorithm has a better stability than GN, Fast-Newman (FN), and N-cut algorithms.

Transient Dynamics of Archaea and Bacteria in Sediments and Brine Across a Salinity Gradient in a Solar Saltern of Goa, India.

The microbial fluctuations along an increasing salinity gradient during two different salt production phases – initial salt harvesting (ISH) phase and peak salt harvesting (PSH) phase of Siridao solar salterns in Goa, India were examined through high-throughput sequencing of 16S rRNA genes on Illumina MiSeq platform. Elemental analysis of the brine samples showed high concentration of sodium (Na+) and chloride (Cl–) ions thereby indicating its thalassohaline nature. Comparison of relative abundance of sequences revealed that Archaea transited from sediment to brine while Bacteria transited from brine to sediment with increasing salinity. Frequency of Archaea was found to be significantly enriched even in low and moderate salinity sediments with their relative sequence abundance reaching as high as 85%. Euryarchaeota was found to be the dominant archaeal phylum containing 19 and 17 genera in sediments and brine, respectively. Phylotypes belonging to Halorubrum, Haloarcula, Halorhabdus, and Haloplanus were common in both sediments and brine. Occurence of Halobacterium and Natronomonas were exclusive to sediments while Halonotius was exclusive to brine. Among sediments, relative sequence frequency of Halorubrum, and Halorhabdus decreased while Haloarcula, Haloplanus, and Natronomonas increased with increasing salinity. Similarly, the relative abundance of Haloarcula and Halorubrum increased with increasing salinity in brine. Sediments and brine samples harbored about 20 and 17 bacterial phyla, respectively. Bacteroidetes, Proteobacteria, and Chloroflexi were the common bacterial phyla in both sediments and brine while Firmicutes were dominant albeit in sediments alone. Further, Gammaproteobacteria, Alphaproteobacteria, and Deltaproteobacteria were observed to be the abundant class within the Proteobacteria. Among the bacterial genera, phylotypes belonging to Rubricoccus and Halomonas were widely detected in both brine and sediment while Thioalkalispira, Desulfovermiculus, and Marinobacter were selectively present in sediments. This study suggests that Bacteria are more susceptible to salinity fluctuations than Archaea, with many bacterial genera being compartment and phase-specific. Our study further indicated that Archaea rather than Bacteria could withstand the wide salinity fluctuation and attain a stable community structure within a short time-frame.

Species Diversity Characteristics of a Natural Pinus taiwanensis Community with Different Diameter Classes and Forest Densities

Pinus taiwanensis is a species endemic to China. This study selected four typical plots of Pinus taiwanensis in the natural secondary forest around Macheng City, in order to reveal the characteristics of and the relationships between different diameter classes (determined based on the diameter at breast height or DBH), forest densities and species diversity, as well as the similarities of species diversity of different plots within the community. The result showed that Pinus taiwanensis was the dominant species in the community. The ratio of Pinus taiwanensis trees of diameter class IV reached a peak of 19.46% of the total followed by diameter class VII at 18.92%. The study recorded 156 species of vascular plants from 130 genera of 71 families; Pinus taiwanensis was the dominant species in the community. When the forest density was 1200 trees ha–1 with the largest average diameter of DBH=36.779±4.444 cm, the diversity (Shannon index H'=1.6716) and the evenness (Pielou index E=0.6727) of the tree layer was the highest. When the forest density reached 1525 trees ha–1 with the lowest average diameter of DBH=18.957±5.141 cm, the richness (Dma=5.4308), the diversity (H'=2.9612) and the evenness (E=0.8985) of all shrub layers climbed to the maximum. When the forest density was 1325 trees ha–1, the richness (Dma=5.8132), the diversity (H'=3.0697) and the evenness (E=0.9025) of all herb layers peaked. In terms of vertical structure, the average diversity indexes were herb layer>shrub layer>tree layer. High canopy density weakened light intensity in the community, causing a reduction in the species diversities of herbs and shrubs. The average similarity coefficient between the sample plots was 0.3356, which was at the medium dissimilarity level. External disturbances and improper management were major contributors to the low species diversity of the community. The implementation of scientific management measures is urgently needed to optimize the forest structures of Pinus taiwanensis, create a benign community environment, and promote species diversities and establish a stable forest community structure.