[Structural Characteristics of Phytoplankton Communities and Its Relationship with Environmental Factors in a Group of Drinking Water Reservoirs by Water Transmission from Modaomen Waterway in Zhuhai]

Modaomen Waterway is the main outlet of the Pear River system and an important water source for Zhuhai and Macao. The water quality of 13 sampling sites in Modaomen Waterway, phytoplankton, and environmental factors were investigated at 21 sampling sites in 4 drinking water source groups, which transport water from Modaomen Waterway and connect with each other, in August and October of 2021. A total of 73 genera of phytoplankton in eight phyla were identified, with a total of 150 species, most of them belonging to Cyanophyta, Chlorophyta, and Bacillariophyta. The relative abundance of Cyanophyta was higher than 90% in the DJS and YL reservoirs during flood and dry seasons; Cyanophyta, Chlorophyta, and Bacillariophyta were dominant phyla during different seasons; and their distribution was balanced in the ZXD and ZY reservoirs. The Shannon-Wiener index, Pielous uniformity index, and Margalef richness index showed that the ZY reservoir had the most abundant biodiversity, which indicated the best water quality, followed by the ZXD and YL reservoirs. Conversely, the DJS was the least diverse reservoir for phytoplankton. The PCoA analysis indicated significant differences in plankton structures in ZXD and ZY with the other two reservoirs (P<0.05), respectively. Redundancy analysis (RDA) showed that the main environmental factors affecting the distribution of the phytoplankton community were NO₃^-, TOC, TP, Cl^-, and NH₄⁺-N. These results indicated that the phytoplankton community of the four reservoirs were greatly affected by the nutrient salt caused by water transport, which suggested that the water quality of Modaomen Waterway should be improved to increase reservoir water nutrition to ensure the safety of drinking water sources.

[Changes in Soil Bacterial Community Diversity in Degraded Patches of Alpine Meadow in the Source Area of the Yellow River]

MiSeq sequencing technology was used to investigate the bacterial compositions and diversities of active patch, non-active patch, recovered patch, and healthy alpine meadows so as to understand the changes in soil bacterial community diversity during altitude change and alpine meadow degradation. The relationship between bacterial diversity and environmental factors was analyzed using redundancy analysis (RDA). The results showed that the dominant bacterial phyla in the soil included Proteobacteria, Actinobacteriota, and Acidobacteriota in the study areas. The dominant bacterial genera that were identified via the MiSeq were RB41, Sphingomonas, and Bradyrhizobium. The relative abundance of these genera decreased with altitude increase and increased with the restoration progress of degraded patches but was significantly lower than that in the alpine meadow (P<0.05). The abundance of functional bacteria related to carbon fixation in degraded patches was higher than that in the healthy alpine meadow. The bacterial Chao1 index and species number in different types of degraded patches were significantly higher than those in the alpine meadow (P<0.05). The results of the RDA suggest that biological soil crust coverage and total nitrogen were the main influencing factors on dominant bacterial phyla at the altitude of 4013 m. Biomass, total nitrogen, and pH had a great influence on the dominant bacterial phyla at the altitude of 4224 m. Biomass and total potassium significantly affected the distribution of bacterial genera at the altitude of 4013 m. Sedge coverage and available nitrogen were the main influencing factors on bacterial dominant genera at the altitude of 4224 m. Biological soil crusts and pH had a great influence on bacterial diversities. The bacterial influence factors varied greatly at different altitude areas. Therefore, we should not only pay attention to the effect of alpine meadow degradation but also consider the effect of altitude in the study of bacterial diversity changes.

[Characteristics of Microbial Community Structure in the Surrounding Farmlands of a Mercury Mining Area and Its Environmental Driving Factors]

In order to investigate the characteristics of soil microbial community structure and their relationships with environmental factors in the surrounding farmlands of a mercury mining region, we analyzed soil physical and chemical properties, Hg pollution, enzyme activity, and microbial community structure characteristics in the surrounding farmlands of a mercury mining region in Tong Ren (Bahuang Town, Bijiang District; Huaqiao Town, Shiqian County; Kaide Town, Jiangkou County; and Chuantong town, Bijiang District; referred to as BJ, SQ, JK, and TR, respectively). The relationships between the characteristics of soil microbial community structure and environmental factors were determined using redundancy analysis (RDA) and correlation network analysis. The results showed that the degree of soil Hg contamination varied depending on the sampling locations in the study region. The soils in JK and TR were categorized as having light-level Hg contamination, whereas those in SQ and BJ were at moderate-level Hg contamination. The potential ecological risk indicated that the soil suffered different degrees of Hg contamination (TR was at a medium level, BJ and JK were at a serious level, and SQ was at a high severe level of pollution). The dominant bacteria flora were Proteobacteria, Actinobacteria, Acidobacteria, and Chloroflexi, whereas the dominant flora of fungi included Ascomycota, Basidiomycota, and Mortierellomycota. RDA analysis showed that pH, sucrase (SC), and catalase (CAT) activities were the key environmental factors of soil bacterial community structure. Soil pH, available nitrogen (AN), available potassium (AK), HCl-Hg, acid phosphatase (ACP), and urease (URE) activities were the key environmental factors that affected soil fungal community structure. Correlation network analysis indicated that pH, available phosphorus (AP), HCl-Hg, SC, ACP, and CAT were the key environmental factors affecting soil bacterial community structure, including Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, Firmicutes, Rokubacteria, and Planctomycetes. AK, pH, total nitrogen (TN), AP, AN, ACP, URE, and SC activities were the key environmental factors affecting soil fungal community structure, such as Ascomycota, Basidiomycota, Mortierellomycota, Glomeromycota, Chytridiomycota, Rozellomycota, Kickxellomycota, and Mucoromycota.

[Temporal and Spatial Variations in Water Quality of Hanjiang River and Its Influencing Factors in Recent Years]

Hanjiang River is the main water source and influence area of the Middle Route of the South to North Water Transfer Project. In recent years, the water quality and ecological environment in the middle and lower reaches of the Hanjiang River has become seriously degraded and water blooms occur frequently. Scientific identification of the temporal and spatial variations in water environment quality (and the main driving factors) has become an important management requirement for optimizing the upstream water transfer project. The temporal and spatial variations and influencing factors of water quality in the Hanjiang River basin were systematically analyzed, based on multi-source data and using the Daniel trend test, Mann Kendall test, K-means cluster analysis, dissimilarity analysis, and redundancy analysis. Results showed that: ① in recent years, the main stream of the Hanjiang River had generally good water quality, which was generally classified as class Ⅱ of GB 3838-2002, while the water quality of some sections in the middle and lower reaches was classified as class Ⅲ. However, the total phosphorus (TP) and total nitrogen (TN) load was relatively high, with 10 stations in the Hanjiang River basin showing averaged concentrations of 0.028-0.263 mg·L^-1 and 0.630-1.852 mg·L^-1, respectively, during 2014-2018. ② From 2004 to 2018, TP and TN at Zongguan station did not show significant variation, and other water quality indexes did not exhibit any regular patterns. The concentrations of TN, NH₄⁺-N, and BOD₅ in the dry season were higher than those in the wet season. In the wet season. the permanganate index showed different variation patterns, while TP concentration did not decrease significantly. ③ Different sections showed obvious differences in the variation of water quality indexes. However, the ten stations can be clustered into three categories: the upstream stations showed the best water quality, followed by the middle reaches, and the downstream stations showed the worst. The water quality at Xiaohe station improved significantly over the study period, which may be related to protection measures implemented in recent years, such as source control, emission reduction, and removal of aquaculture. ④ Water discharge and temperature were important factors affecting the water quality of the three regions in Hanjiang River. According to redundancy analysis, the contribution of discharge to water quality in the upstream and downstream areas was much larger, while the contribution of water temperature was greatest in the middle reaches of the river.

[Spatial and Temporal Variation of Phytoplankton Community Structure and Its Influencing Factors in Shanghai River Channels]

In order to explore the spatial and temporal characteristics of the phytoplankton community structure and its influencing factors in Shanghai rivers, the water quality and phytoplankton community structure at 44 river channel sites in a central urban area, new town area, and rural area in Shanghai were investigated from September to October 2018 (autumn) and July to August 2019 (summer). The results showed that:① Chlorophyta was the dominant phyla during the autumn and summer, and was followed by Cyanobacteria and Bacillariophyta. Cyanobacteria dominated the phytoplankton community in terms of density. The number of species and density of phytoplankton were 24% and 2.77 times higher, respectively, than those during the summer and autumn. The dominance of Microcystis sp. was obvious during the autumn (Y=0.16), but there was no absolute dominant species during the summer. ② The difference in the number of phytoplankton species among the three regions was not significant, and the density of the total phytoplankton and cyanobacteria species showed a similar spatial pattern:rural area > new town area > central urban area. Additionally, no significant difference was observed in the total phytoplankton and Cyanobacteria density among the three regions during the autumn (P>0.05), whereas it was 1.82 and 1.93 times higher, respectively, in the rural area in comparison to the central urban area during the summer (P<0.05). Montecarlo test results revealed that the main factors affecting the phytoplankton community structure during the autumn were secchi disk transparency (SD), total phosphorus (TP), total nitrogen (TN), and turbidimetry (Turb), whereas these were TN, Turb, SD, and pH during the summer. ③ The results of a redundancy analysis (RDA) indicated that during the autumn, the phytoplankton in the rivers of the new town area were mainly affected by Turb, TN, and TP, while the rural rivers were mainly affected by SD. During the summer, the phytoplankton in the rivers of the new town and rural areas were mainly affected by TN and Turb. The influencing factors in the central urban area were complex.

[Effect of Porous Fillers Properties on Biofilm Growth]

As an important part of biological aerated filters (BAFs), porous fillers are key to the effectiveness of BAF wastewater treatment. At present, there are many types of fillers, but the influence of the surface physical and chemical properties on biofilm formation is unclear, and how to compare and select the best biological filler remains a difficult problem in BAF engineering applications. In this study, the physical and chemical characteristics of several porous biological fillers that are commonly used in BAFs were studied, and the correlation between their physical/chemical properties and the biofilm attachment and enzyme activity of the biofilm on the filler was investigated. The results showed that the sponge filler could easily absorb sludge, but also clogged easily and the overall biofilm activity was not high. The three-dimensional hollow filler had a low surface-adsorbed biomass, but the specific surface area was large and the surface attachment growth biofilm activity was relatively strong. Ceramsite had a good hydrophilicity and high surface roughness, and the zeta potential was the most positive. Moreover, microorganisms easily attached and grew, it had the strongest sludge adhesion performance, and the best biofilm activity. According to a redundancy analysis (RDA), the main factor affecting the biomass on the surface of the fillers was the zeta potential, whereas the main factors affecting the surface sludge activity of the fillers was the clearance rate. According to the removal load of NH₄⁺-N by six groups of reactors, the removal load of NH₄⁺-N by ceramsite was the largest [68 g·(m³·d)^-1], and was followed by volcanic rocks [67 g·(m³·d)^-1]. Combined with the above factors, ceramsite was determined to be the most suitable filler for BAF.

[Distribution Characteristics and Influencing Factors of Chromophoric Dissolved Organic Matter in a Northern-Side River of the Qinling Mountains in Summer]

UV-visible absorption spectroscopy, fluorescence spectroscopy, and parallel factor analysis were used to analyze the composition of chromophoric dissolved organic matter (CDOM) in the waters of the Wangchuan River in summer, and the source of this CDOM was explored. The redundant analysis method and Pearson correlation were used to analyze the correlation between optical parameters and water quality parameters. The results showed that the CDOM of the Wangchuan River is composed of the tryptophan-like component C1 (245, 300/335 nm), the short-wave humus component C2 (240, 320-340/405 nm), and the long-wave humus component C3 (270, 350-370/470 nm), in which components C1 and C2 have some homology (r=0.859, P<0.001). CDOM absorption coefficient α(355) indicates that the CDOM concentration in the water body of the Wangchuan River is at a low level, and the correlation between α(355) and DOC concentration is significant (r=0.850, P<0.001), which is conducive to the establishment of a DOC inversion model. Water fluorescence index FI (2.36±0.20), HIX (3.66±2.47), BIX (1.56±0.82), and freshness index (β:α) (1.33±0.62), and the spectral slope ratio S_R (0.76±0.25) indicate that the CDOM of the Wangchuan River has strong self-generated characteristics, weak humification characteristics, and more new CDOM. Redundancy analysis showed that the humic components (C2, C3) are affected by algae metabolism and microbial action, while tryptophan-like components (C1) are related to land-based input, and negatively correlated with dissolved total nitrogen. The humic components C2 and C3 are positively correlated with total phosphorus, dissolved total phosphorus, and dissolved organic carbon. This paper clarifies the characteristics and influencing factors of CDOM in the Qinling valley, and provides a theoretical basis for water body management in the Qinling valley.

[CDOM Optical Characteristics and Related Environmental Factors of High-turbidity Waters on the Loess Plateau]

Chromophoric dissolved organic matter (CDOM) optical absorption characteristics, CDOM spectral slopes (S_275-295), contribution of each component to water absorption, and the effects of environmental factors on them were analyzed to determine the sources and composition of CDOM in high-turbidity waters on the Loess Plateau. Samples in rivers and lakes (saline and freshwater) in the Loess Plateau area of Shaanxi and Inner Mongolia were collected in May 2018. The results demonstrated significant differences in CDOM absorption optical characteristics between rivers and lakes. The average a_CDOM(440) (CDOM concentration, 8.45 m^-1) in lakes was higher than that of rivers (2.70 m^-1), and the saline lakes showed a higher CDOM concentration (13.52 m^-1) than the freshwater lakes (3.38 m^-1). Moreover, the light utilization efficiency of freshwater lakes is higher than that of saline lakes and turbid rivers. Great differences in pH and dissolved organic carbon (DOC) were observed between different types of water (P<0.01). The differences in electrical conductivity (EC), turbidity (Tur), and total suspended matter concentration (TSM) were significant with no statistical significances (P>0.1). The chlorophyll a concentration (Chla) in saline lakes was close to the Chla concentration in freshwater lakes if extreme values were excluded. In addition, the CDOM molecular weights of lake water were lower than those in the rivers, while CDOM molecular weights in saline lakes were lower than those in freshwater lakes based on the S_275-295. Analyses of specific ultraviolet absorbance (SUVA₂₅₄) were also conducted to determine the sources of CDOM in different water types, and the results showed that the more terrigenous humus were brought into the rivers and saline lakes compared with the freshwater lakes. Redundancy analysis (RDA) indicated that river and lake water quality parameters of the cumulative variance explained rates were 35.2% for river samples and 61.4% for lake samples, and 100% for samples in the saline and freshwater lakes individually. The results of RDA showed that dissolved oxygen (DO), water temperature, and EC exerted significant effects on CDOM optical properties of the river (P<0.01), while DOC, TSM, and Tur had a great influence on the CDOM optical properties of lakes (P<0.01). There was a strong correlation between pH and CDOM in the saline lakes, while DOC was significantly correlated with CDOM in the freshwater lakes (P<0.05).

[Environmental Response and Ecological Function Prediction of Aquatic Bacterial Communities in the Weihe River Basin]

The diversity of bacterial communities and their metabolic function in the waters of the Weihe River Basin are of great significance for water pollution remediation, ecological restoration, and water quality assessment. Illumina MiSeq high-throughput sequencing technology was applied to study the bacterial community distribution characteristics after the comprehensive treatment of the Shaanxi part of the Weihe River Basin. Furthermore, the correlation between the bacterial communities and environmental factors was analyzed by redundancy analysis (RDA), and the PICRUSt method was adopted to evaluate the ecological function of the bacterial communities. The results showed that Proteobacteria, Actinobacteria, Cyanobacteria, and Bacteroidetes were the main bacterial communities in the water, accounting for 85% of the total microbial community. Additionally, these bacteria showed a significant positive correlation (P=0.02, <0.05) with the TP, NO₂^--N, NO₃^--N, and TN. The bacteria community richness of water samples collected in Zaohe River was the lowest of all samples, while which in the downstream of the junction of Bahe river and Weihe river was the highest. In addition, water in the Weihe River Basin had great impact on the endocrine systems of aquatic organisms, and also had a possibility of infectious diseases for humans. Our research provides a theoretical basis for the safe and sustainable development of the water environment in the Weihe River Basin.

[Community Structure Characteristics of nirS Denitrifying Bacteria of Spring Typical Parkland Waterbodies in Shijiazhuang City]

Four typical park water bodies located in the main urban area of Shijiazhuang city were selected to study the relationships between water quality and the community structure and diversity of nirS denitrifying bacteria. The results showed that the nitrogen concentration ranged from 4.43 to 13.83 mg·L^-1 in four park water bodies, which exhibited notable nitrogen pollution characteristics. Based on the characteristic index analysis of three-dimensional fluorescence spectra, the four park water bodies all exhibited strong autochthonous components and low humus characteristics. The results of Illumina high-throughput sequencing indicated that most of the nirS denitrifying bacteria showed significant differences in dominant genus. The unclassified_Bacteria (53.52%), Pseudomonas (60.48%), and Rhodobacter (46.94%) were the dominant bacteria in Yuxi park, Shuishang park, and Chang'an park, respectively. In comparison, unclassified_Bacteria (36.19%) and unclassified_Proteobacteria (23.44%) were the dominant bacteria in Shiji park. Redundancy analysis showed that denitrification bacteria in Yuxi park were mainly affected by nitrate, total nitrogen, and dissolved oxygen; denitrification bacteria in Shuishang park were greatly affected by total phosphorus; denitrification bacteria in Chang 'an park were mainly affected by ammonia and nitrous nitrogen; and denitrification in Shiji park were mainly affected by total phosphorus, nitrite, and ammonia. Overall, the water quality and the community structure of nirS denitrification bacteria exhibited significant differences in park water bodies. Further research could contribute to the understanding of water quality characteristics and the denitrifying community structure of urban water systems, and develop efficient denitrifying bacterial agents.

Analyzing community structure subject to incomplete sampling: hierarchical community model vs. canonical ordinations

Recently developing hierarchical community models (HCMs) accounting for incomplete sampling are promising approaches to understand community organization. However, pros and cons of incorporating incomplete sampling in the analysis and related design issues remain unknown. In this study, we compared HCM and canonical redundancy analysis (RDA) carried out with 10 different dissimilarity coefficients to evaluate how each approach restores true community abundance data sampled with imperfect detection. We conducted simulation experiments with varying numbers of sampling sites, visits, mean detectability and mean abundance. Performance of HCM was measured by estimates of "expected" (mean) abundance ( λ ^ ij ) and realized abundance ( N ^ ij : direct estimate of site- and species-specific abundance). We also compared HCM and different types of RDA (normal, partial, and weighted), all performed with the same ten different dissimilarity coefficients, with unequal number of visits to sampling sites. In addition, we applied the models to a virtual survey carried out on the Barro Colorado Island tree plot data for which we know true community abundance. Simulation experiments showed that N ^ ij yielded by HCM best restored the underlying abundance of constituent species among 12 abundance estimates by HCM and RDA regardless if the sampling was equal or unequal. Mean abundance predominantly affected the performance of HCM and RDA while λ ^ ij yielded by HCM had comparable performance to percentage difference and Gower dissimilarity coefficients of RDA. Relative performance of RDA types depended on the combination of dissimilarity coefficients and the distribution of sampling effort. Best performance of N ^ ij followed by λ ^ ij , percentage difference and Gower dissimilarity were also observed for the analysis of tree plot data, and graphical plots (triplots) based on λ ^ ij rather than N ^ ij clearly separated the effects of two environmental covariates on the abundance of constituent species. Under our conditions of model evaluation and the method, we concluded that, in terms of assessing the environmental dependence of abundance, HCMs and RDA can have comparable performance if we can choose appropriate dissimilarity coefficients for RDA. However, since HCMs provide straightforward biological interpretations of parameter estimates and flexibility of the analysis, HCMs would be useful in many situations as well as conventional canonical ordinations.

[Low-carbon behavioral performance of scenic spots and the driving mechanism: A case study of Zhangjiajie World Heritage Site.]

Low-carbon behavior of scenic spots has direct influence on coordinated and orderly development of eco-environment and socio-economic system in World Heritage Site. Five level-one indicators and 38 level-two indicators were respectively established to systematically measure the low-carbon behavioral performance (LCBP) of scenic spots in Zhangjiajie, the seat of World Natural Heritage. ANOVA and Bonferroni analysis were applied to compare the LCBP of scenic spots in different groups. The redundancy analysis and Monte Carlo permutation were used to figure out the main driving factors that affect scenic area&rsquo;s LCBP. Results showed that 32 scenic spots&rsquo; LCBP was excellent in general, with a weighted mean value of 3.10. The group mean of perfor-mance in low-carbon design, daily energy conservation, water saving management, waste reduction and low-carbon awareness was 0.49, 0.74, 0.24, 1.51 and 0.11, separately. Huanglong Cave performed the best (4.193) and He Long&rsquo;s Former Residence performed the worst (2.400) in the 32 scenic spots. The scores of 5A, 4A and 3A or no A scenic spots showed no significant difference in most low-carbon behavior indicators, only 11 indicators reflected significant difference among diffe-rent groups. Pressures from investors, administration committee, tourists and local government were main driving factors for low-carbon behavior of scenic spots.

[Spatial Variation of Soil Organic Carbon and Stable Isotopes in Different Soil Types of a Typical Oasis]

Soil organic carbon (SOC) and its stable isotope composition reflect important information on ecosystem carbon cycle. Under the background of global change, it is of great significance to study carbon dynamics and sustainable development of carbon resources in terrestrial ecosystems. In this study, four soil types in Alar oasis were studied to determine SOC content and δ¹³ C value at different layers, and the differences of δ¹³C_SOC abundance and its relationship with soil environmental factors were also discussed. Three main outcomes were drawn from the results. ①The total organic carbon (TOC) content of the soil was in the order of irrigated desert soil > brown desert soil > saline soil > aeolian sandy soil, and had a higher value in the surface layer (0-20 cm layer); δ¹³C_SOC ranged from -26‰--23‰, the surface layer (0-20 cm) was in the order saline soil > aeolian sandy soil > irrigated desert soil > brown desert soi. ② Both SOC and δ¹³C_SOC were significantly affected by soil type and their interaction, and by soil depth. Furthermore, the effect test of interaction indicated that SOC was significantly impacted by environmental factors, but the impact on δ¹³C_SOCwas relatively weak. ③ The results of redundancy analysis showed that SOC had a significant or extremely significant positive correlation with soil inorganic carbon, total nitrogen, soil water content and bulk density, and had a significant negative correlation with C/N. There was also a significant positive correlation between δ¹³C_SOC and conductivity, and in addition, δ¹³C_SOC was negatively correlated with soil inorganic carbon and soil water content. The analyses showed that SOC and its isotopes changed with soil types, and that the effect of soil type was stronger than that of soil depth, which was mainly determined by soil moisture content.

Spatial Distribution Patterns of Root-Associated Bacterial Communities Mediated by Root Exudates in Different Aged Ratooning Tea Monoculture Systems

Positive plant-soil feedback depends on beneficial interactions between roots and microbes for nutrient acquisition; growth promotion; and disease suppression. Recent pyrosequencing approaches have provided insight into the rhizosphere bacterial communities in various cropping systems. However; there is a scarcity of information about the influence of root exudates on the composition of root-associated bacterial communities in ratooning tea monocropping systems of different ages. In Southeastern China; tea cropping systems provide the unique natural experimental environment to compare the distribution of bacterial communities in different rhizo-compartments. High performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS) was performed to identify and quantify the allelochemicals in root exudates. A high-throughput sequence was used to determine the structural dynamics of the root-associated bacterial communities. Although soil physiochemical properties showed no significant differences in nutrients; long-term tea cultivation resulted in the accumulation of catechin-containing compounds in the rhizosphere and a lowering of pH. Moreover; distinct distribution patterns of bacterial taxa were observed in all three rhizo-compartments of two-year and 30-year monoculture tea; mediated strongly by soil pH and catechin-containing compounds. These results will help to explore the reasons why soil quality and fertility are disturbed in continuous ratooning tea monocropping systems; and to clarify the associated problems.

[Succession of Phytoplankton Assemblages and Its Influencing Factors in Tangpu Reservoir, Zhejiang Province]

In order to explore the spatial-temporal dynamics of phytoplankton assemblages and its influencing factors in Tangpu Reservoir, phytoplankton and environmental variables were monthly monitored in 2011. The results showed that a total of 115 species of phytoplankton were identified, which belonged to 7 phyla and 62 genera. Phytoplankton abundance varied monthly with the maximum value (20.88×10⁶ cells·L^-1) in April and minimum (0.59×10⁶ cells·L^-1) in June. Variation partitioning of species data matrix showed that the variation of phytoplankton communities among months (account for 72.3%) was much larger than that among sampling sites (account for 2.5%), which indicated that phytoplankton communities had a high temporal but low spatial heterogeneity. Dominant species showed a marked seasonal succession pattern: diatom and blue-green algae species in spring, blue-green algae and green algae species in summer, diatom and cryptomonads species in autumn and winter. Result of multivariate analysis (RDA) indicated that HRT was the key factor affecting the shift between hydrological disturbance sensitive and tolerant species, and the formation of spring algal bloom; SiO₂, WT and N:P were the key factors affecting the shift from diatom and cryptomonads species to blue-green algae and green algae species.

Distribution and diversity of fungi in freshwater sediments on a river catchment scale

Fungal communities perform essential functions in biogeochemical cycles. However, knowledge of fungal community structural changes in river ecosystems is still very limited. In the present study, we combined culture-dependent and culture-independent methods to investigate fungal distribution and diversity in sediment on a regional scale in the Songhua River catchment, located in North-East Asia. A total of 147 samples over the whole river catchment were analyzed. The results showed that compared to the mainstream, the tributaries have a higher fungal community organization and culturable fungal concentration, but possess lower community dynamics as assessed by denaturing gradient gel electrophoresis (DGGE). Furthermore, phylogenetic analysis of DGGE bands showed that Ascomycota and Basidiomycota were the predominant community in the Songhua River catchment. Redundancy analysis revealed that longitude was the primary factor determining the variation of fungal community structure, and fungal biomass was mainly related to the total nutrient content. Our findings provide new insights into the characteristics of fungal community distribution in a temperate zone river at a regional scale, and demonstrate that fungal dispersal is restricted by geographical barriers in a whole river catchment.

Relating microbial community structure to functioning in forest soil organic carbon transformation and turnover

Forest soils store vast amounts of terrestrial carbon, but we are still limited in mechanistic understanding on how soil organic carbon (SOC) stabilization or turnover is controlled by biotic and abiotic factors in forest ecosystems. We used phospholipid fatty acids (PLFAs) as biomarker to study soil microbial community structure and measured activities of five extracellular enzymes involved in the degradation of cellulose (i.e., β-1,4-glucosidase and cellobiohydrolase), chitin (i.e., β-1,4-N-acetylglucosaminidase), and lignin (i.e., phenol oxidase and peroxidase) as indicators of soil microbial functioning in carbon transformation or turnover across varying biotic and abiotic conditions in a typical temperate forest ecosystem in central China. Redundancy analysis (RDA) was performed to determine the interrelationship between individual PFLAs and biotic and abiotic site factors as well as the linkage between soil microbial structure and function. Path analysis was further conducted to examine the controls of site factors on soil microbial community structure and the regulatory pathway of changes in SOC relating to microbial community structure and function. We found that soil microbial community structure is strongly influenced by water, temperature, SOC, fine root mass, clay content, and C/N ratio in soils and that the relative abundance of Gram-negative bacteria, saprophytic fungi, and actinomycetes explained most of the variations in the specific activities of soil enzymes involved in SOC transformation or turnover. The abundance of soil bacterial communities is strongly linked with the extracellular enzymes involved in carbon transformation, whereas the abundance of saprophytic fungi is associated with activities of extracellular enzymes driving carbon oxidation. Findings in this study demonstrate the complex interactions and linkage among plant traits, microenvironment, and soil physiochemical properties in affecting SOC via microbial regulations.