The role of phytoplankton in pollutant transfer processes in rivers. Example of River Marne (France)

The impact of the spring phytoplanktonic blooms on the partition of nutrients and metals between the dissolved and particulate phases was studied over two years in the river Marne, upstream of its confluence with the river Seine. Particular attention was devoted to copper and manganese, determined in the dissolved phase (< 0.22 m), subdivided into the colloidal phase and the 'truly dissolved' phase (< 10 KDaltons) obtained by tangential ultrafiltration. During the algal growth peaks, a sharp reduction of nutrients was observed in the dissolved phase: in 1994, consumption of 70% of silica, 50% of ammonium and 40% of soluble phosphorus present before the phytoplanktonic bloom.The water concentration peaks of suspended matter (SM) and of particulate metals, phosphorus and carbon coincide with those of chlorophyll. The highly significant correlations between pH and chlorophyll (r = 0.92, P < 0.001), pH and SM (r = 0.97, P < 0.001) and chlorophyll and SM (r = 0.93, P < 0.001) confirmed the phytoplanktonic nature of SM and the determining role of pH in the partition of metals, its increase being responsible for the coprecipitation of metal. As a corollary to the increase in the particulate phase, a decrease of 55% was observed for copper and manganese in the 'truly dissolved' phase compared to the concentrations outside bloom periods.The importance of the colloidal fraction was also shown. During the strong algal growth periods, the proportion of 'colloidal metal' in the dissolved phase (< 0.22 m) reached 60% and the increase in the colloidal fraction was 4 times stronger for copper than for manganese. While manganese seemed to be more associated with macroparticles, copper was more associated with fine colloidal biological particles intrinsic to the phytoplankton.     

Salinity gradient and nutrients as major structuring factors of the phytoplankton communities in salt marshes

This study investigated the major environmental factors structuring, for a year, phytoplankton assemblages in the Sfax saltern (Tunisia): salinity and nutrients. A STATICO analysis based on 11 environmental variables and the abundances of 64 phytoplanktonic species was conducted. STATICO is used to analyze the stable part of the relationships between the environment and species, and then to determine how these relationships change over time. The analysis confirmed that the salinity gradient had a considerable influence on the composition of the phytoplanktonic communities. Bacillariophyceae and Dinophyceae dominated in the least salty ponds, whereas Chlorophyceae and Cyanophyceae dominated in the saltiest ponds, in accordance with the halotolerance level estimated for each species by calculating the optimum salinity and salt tolerance. Nitrogen (N) and phosphorus (P) ions could have a secondary influence on the phytoplankton distribution and its dynamics. Dinophyceae seem to be favored by high ammonium (NH₄ ⁺) concentrations, whereas diatoms seem to be favored by high orthophosphates (PO₄ ^3?) and nitrates (NO₃ ^?) values. The Chlorophyceae Dunalliela salina thrived in the saltiest ponds when the NO₃ ^? concentrations increased.     

The effect of environmental parameters and cyanobacterial blooms on phytoplankton dynamics of a Portuguese temperate Lake

The increasing occurrence of cyanobacterial blooms in freshwaters is of great concern due to the ability of many cyanobacteria to produce cyanotoxins. In the present work, the eutrophied Vela Lake (Central Portugal), used for recreational purposes and as a water source for agriculture, was monitored every fortnight between 2000 and 2001. Phytoplankton diversity and densities were measured and correlated to environmental parameters. A seasonal phytoplanktonic succession was observed and it was mainly correlated with conductivity, temperature, total suspended solids and nutrients availability (particularly phosphorus). Diatoms were dominant during winter months (inferior temperatures and higher nutrients availability) followed by green algae in early spring and then cyanobacteria from late spring until early autumn (less nutrient availability and higher temperatures). A massive cyanobacterial bloom of Aphanizomenon flos-aquae occurred early in May 2001 and was preceded by the lowest nitrogen levels measured in the water during all the study period. At the time of this bloom senescence, dissolved oxygen was severely depleted and a massive death of ichthyofauna was recorded. A Microcystis aeruginosa bloom was also detected in July 2001 and it occurred following a rapid decrease in abundance of green algae and diatoms. By considering not only the environmental parameters but also the occurrence of cyanobacterial blooms as explanatory variables in a canonical correspondence analysis, the variance explained for the phytoplanktonic assemblage during the study period was increased in about 7% achieving a total of 61.0%, indicating a correlation that may be due to the known competitive advantage and/or allelopathy of the bloom-forming cyanobacteria towards microalgae.     

Remediation of Urban River Water by Pontederia Cordata Combined with Artificial Aeration: Organic Matter and Nutrients Removal and Root-Adhered Bacterial Communities

Macrophyte combined with artificial aeration is a promising in situ remediation approach for urban rivers polluted with nutrients and organic matter. However, seasonal variations and aeration effects on phytoremediation performance and root-adhered microbial communities are still unclear. In this study, Pontederia cordata was used to treat polluted urban river water under various aeration intensities. Results showed that the highest removal efficiencies of chemical oxygen demand (COD_Cr) and total nitrogen (TN) were attained under aeration of 30 L min^?1 in spring and summer and 15 L min^?1 in autumn, while total phosphorus (TP) removal reached maximum with aeration of 15 L min^?1 in all seasons. Moderate aeration was beneficial for increasing the diversity of root-adhered bacteria communities, and the shift of bacterial community structure was more pronounced in spring and autumn with varying aeration intensity. The dual effect, i.e. turbulence and dissolved oxygen (DO), of aeration on the removal of COD_Cr and TN prevailed over the individual effect of DO, while DO was the most influential factor for TP removal and the root-adhered bacterial community diversity. P. cordata combined with 15 L min^?1 aeration was deemed to be the best condition tested in this study.     

博斯腾湖湖滨湿地植物多样性对季节变化的响应

研究生物多样性对季节的响应对于维持生态系统稳定、保护生物多样性、解析群落构建机制具有重要意义。本文以博斯腾湖湖滨湿地为研究对象,探究不同季节植物群落的物种多样性与功能多样性的变化规律。结果显示：(1)物种多样性指数随季节变化没有显著改变;功能多样性指数中,功能丰富度由春季到夏季逐渐减小,功能离散度逐渐增大;不同季节的功能均匀度差异性不显著;(2)植物功能性状在不同季节间差异显著;春季叶绿素含量显著低于夏季;夏季比叶面积和叶干物质含量显著高于秋季;叶片含水量和厚度由春季到秋季呈递增趋势;(3)影响Pielou指数和功能丰富度的主要环境因子分别为土壤铵态氮和速效磷;影响Shannon-Wiener指数、Simpson指数和功能均匀度的主要环境因子为土壤有机质;影响功能离散度的主要环境因子为土壤含水量;(4)影响最大株高的主要环境因子为土壤pH值;影响叶干物质含量的主要环境因子为土壤速效钾;影响叶片厚度和比叶面积的主要环境因子为土壤总磷;而影响叶片含水量的主要环境因子为土壤硝态氮;叶绿素含量与土壤因子无显著相关关系。     

Assessing nutrient salts and trace metals distributions in the coastal water of Jeddah,Red Sea

In this study, eighteen sites at Jeddah coastal area, Red Sea, have been assessed for water quality status, depending on nutrients, metals, Chlorophyll-a (Chl-a) and physical variables during 2018 and 2019. The investigated parameters of the Water Quality Index (WQI) are temperature, pH, salinity, dissolved oxygen (DO), DO saturation, oxidizable organic matter (OOM), suspended particulate matter (SPM), Chl-a, ammonium, nitrite, nitrate, total nitrogen, reactive phosphate, total phosphorus, silicate, Zn, Fe, Mn Cu, Cd, Pb, and Ni. The results revealed that the pH values were slightly alkaline with a range of 7.85–8.20. The results of other parameters were as follow: salinity (36.95–42.61PSU), DO (5.22–6.67 mg/L), OOM (0.40–1.23 mg/L), SPM (12.39–21.5 mg/L), Chl-a (0.10–0.83 µg/L). The range of nutrients (μM) were 0.07–0.22, 0.45–1.47, 9.62–18.64, 23.31–57.65, 0.05–0.15, 0.55–2.78 and 2.54–5.51 for NH₄/N, NO₂/N, NO₃/N, TN, PO₄/P, TP and SiO₄/Si, respectively. Cluster analysis was used to classify the stations studied. From the current study, five clusters were found, indicating the need to perform cluster analysis in the water quality assessment process to confirm the durability and consistency of the data discovered in the current application.     

Nutrient and Temperature Limitation of Bacterioplankton Growth in Temperate Lakes

Limitation of bacterioplankton production by nutrients and temperature was investigated in eight temperate lakes in summer. Six of the lakes were resampled in autumn. The lakes differ in nutrient content, water color, and concentration of dissolved organic carbon. Nutrients (phosphorus, nitrogen, and organic carbon) were added alone and in all possible combinations to filtered lake water inoculated with bacteria from the lake. After incubation for 36–40 h at in situ temperatures (ranging from 7 to 20°C), the response in bacterioplankton production was determined. The effect of increased temperature on bacterioplankton growth was also tested. Bacterioplankton production was often limited by phosphorus alone, organic carbon alone, or the two in combination. Phosphorus limitation of bacterioplankton production was more common in the summer, whereas limitation by organic carbon was more frequently observed in the autumn. There was a close balance between limitation by phosphorus and organic carbon in the epilimnion in the summer. In the hypolimnion in the summer, bacterioplankton growth was primarily phosphorus-limited. The effect of phosphorus additions decreased with increasing phosphorus concentrations in the lakes. However, there were no correlations between the effect of added organic carbon and water color, dissolved organic carbon concentration, or phosphorus concentration. When temperature was low (in the hypolimnion in the summer, and throughout the water column in the autumn) temperature also limited bacterioplankton production. Thus, temperature and inorganic nutrients or organic compounds can limit bacterioplankton growth both alone and simultaneously. However, at low temperatures, temperature is the most important factor influencing bacterioplankton growth.     

中小型土壤动物组成对复垦铜尾地土壤养分的影响

通过盆钵生物试验研究了中小型土壤动物不同类群的组成对复垦铜尾矿废弃地土壤养分的影响。整个培养试验根据需求对不同中小型土壤动物组合设置四个处理措施,每种措施分为有无凋落物两种水平,即:(1)无土壤动物(Re),无土壤动物+凋落物(Re+Li)(2)跳虫(Co),跳虫+凋落物(Co+Li)(3)跳虫+蜱螨类(Co+Ac),跳虫+蜱螨类+凋落物(Co+Ac+Li)(4)中小型土壤动物(剔除大型土壤动物Me),中小型土壤动物+凋落物(Me+Li)。另设一组对照(CK)处理,并于培养实验开始前完成测定,作为本底值。分析表明,土壤p H随着中小型土壤动物类群的增加而降低,最低值出现在Me和Me+Li处理,且二者之间无显著性差异;对照(CK)处理下的各养分含量均显著低于其他各处理,各处理中有机质、有效磷和水解性氮的含量的最大值均出现Me+Li处理,且与其他各处理呈极显著差异(P0.01);土壤全磷含量最大值出现在Re和Me+Li处理,最低值出现在Co+Li处理且之间呈显著差异(P0.05);土壤全氮含量最大值出现在Co+Ac和Me+Li处理,最低值出现在Co+Ac+Li处理且彼此间也呈显著差异(P0.05)。相关分析表明,有机质与有效磷以及全氮与水解性氮之间相关性达到极显著正相关关系(r=0.886,r=0.898),有机质与全氮及水解性氮分别呈现显著正相关关系(r=0.735,r=0.780),全氮与有效磷(r=0.782)以及有效磷与水解性氮(r=0.755)也呈现显著正相关关系。p H与有机质呈现显著负相关关系(r=-0.782),全磷与有机质、全氮、有效磷、水解性氮均无相关关系。     

Response and interaction of <Emphasis Type="Italic">Bradyrhizobium japonicum</Emphasis> and arbuscular mycorrhizal fungi in the soybean rhizosphere

Regulatory response and interaction of Bradyrhizobium and arbuscular mycorrhizal fungi (AMF) play a vital role in rhizospheric soil processes and productivity of soybean (Glycine max L.). Nitrogen (N) and phosphorus (P) are essential nutrients for plant growth and productivity, the synergistic interaction(s) of AMF and Bradyrhizobium along with rhizospheric beneficial microorganisms stimulate soybean growth and development through enhanced mineral nutrient acquisition (N and P) and improved rhizosphere environment. Such interactions are crucial, especially under low-input eco-friendly agricultural cropping systems, which rely on biological processes rather than agrochemicals to maintain soil quality, sustainability, and productivity. Furthermore, enhancement of N-fixation by root nodules along with AMF-mediated synergism improves plant P nutrition and uptake, and proliferation of phosphate-solubilizing fungi. However, the genetic and/or allelic diversity among native strains, their genes/enzymes and many environmental factors (e.g., soil organic matter, fertilizers, light, temperature, soil moisture, and biotic interactors) affect the interactions between AMF and Bradyrhizobium. New information is available regarding the genetic composition of elite soybean inoculant strains in maximizing symbiotic performance, N-fixing capabilities and depending on N and P status the host-mediated regulation of root architecture. Overall, for sustainable soybean production systems, a deeper understanding of the interaction effects of Bradyrhizobium and AMF co-inoculation are expected in the future, so that optimized combinations of microorganisms can be applied as effective soil inoculants for plant growth promotion and fitness. The objective of this review is to offer insights into the mechanistic interactions of AMF and Bradyrhizobium and rhizopheric soil health, and elucidate the role of environmental factors in regulating growth, development and sustainable soybean productivity.     

Sensitivity of Heterogeneous Marine Benthic Habitats to Subtle Stressors

It is important to understand the consequences of low level disturbances on the functioning of ecological communities because of the pervasiveness and frequency of this type of environmental change. In this study we investigated the response of a heterogeneous, subtidal, soft-sediment habitat to small experimental additions of organic matter and calcium carbonate to examine the sensitivity of benthic ecosystem functioning to changes in sediment characteristics that relate to the environmental threats of coastal eutrophication and ocean acidification. Our results documented significant changes between key biogeochemical and sedimentary variables such as gross primary production, ammonium uptake and dissolved reactive phosphorus flux following treatment additions. Moreover, the application of treatments affected relationships between macrofauna communities, sediment characteristics (e.g., chlorophyll a content) and biogeochemical processes (oxygen and nutrient fluxes). In this experiment organic matter and calcium carbonate showed persistent opposing effects on sedimentary processes, and we demonstrated that highly heterogeneous sediment habitats can be surprisingly sensitive to subtle perturbations. Our results have important biological implications in a world with relentless anthropogenic inputs of atmospheric CO₂ and nutrients in coastal waters.     

菹草种群内外水质日变化

对菹草(Potamogeton crispus)种群内外水体进行了昼夜连续监测,分析菹草种群内外水质的日变化趋势.结果显示,种群内DO自日出后增加,日落后持续下降,且与水温变化一致,于19:30左右出现1次明显低谷,后略有恢复,后一直降至日出前后;开阔水域DO变化与水温呈现一定相关性,但变化幅度较小;交界处DO含量兼有种群内与开阔水域的变化特点.种群内水体pH值自日出前后升高,日落时达最高值,后开始下降,直至次日出前后;交界处与种群变化趋势一致;开阔水域pH总体变化幅度较小,白天高于夜间,总体DO含量及pH分布:种群区＞交界处＞开阔水域.种群及交界处TN含量均在日出前后达最高,日出后递减,开阔水域夜间含量较高,日出前后达最高;各点NH+4-N变化规律不显著;种群内水体TP含量夜间较高,日出前后达最高值,日出后递减,日落后递增;开阔水域TP含量夜间较高,白天略低;交界处正午前后达最低值,傍晚达最高值,TN、TP总体分布:种群＜交界处＜开阔水域.菹草种群存在对水体DO、pH等环境因子均产生重要影响,继而影响水体内源性氮磷的迁移,其中对pH影响较小,其变化未能影响水体氮磷迁移,而DO昼夜变化较大,对水体内源性氮磷的迁移起重要影响.     

Seasonal changes in bacterial and phytoplankton biomass in a subantarctic coastal area (Kerguelen Islands)

The seasonal variations of bacterial and phytoplanktonic biomass were studied during several pluri-annual surveys in the subantarctic Morbihan Bay (Kerguelen Islands, 49 ° 20 S; 70 ° 10 E). Large interannual variation was observed. Phytoplanktonic biomass showed moderate values during winter and autumn. They increased sharply in spring, reaching a maximum value of about 1 mg C l^–1 corresponding to an important depletion of nutrients. A second phytoplanktonic bloom of similar amplitude occurred in late summer. During algal blooms which were roughly associated with optimal values of solar irradiation for the first one and with the highest temperatures for the second one, phytoplanktonic material represented near 100% of particulate and living carbon. Bacteria showed maximal abundance (0.2 to 0.7 mg C l^–1) during summer or autumn. Their relative abundance, which represented less than 1% of the living biomass in spring and summer, can reach more than 95% in autumn and winter.     

不同林窗马尾松凋落叶与土壤养分变化研究

以现有42年生的马尾松（Pinus massoniana）人工纯林,经过采伐形成4种不同大小有效面积的林窗（100、400、900和1 600 m²）为研究对象,以未经采伐的42年生马尾松人工纯林为对照样地,采用凋落叶分解袋法,研究不同大小有效面积林窗对马尾松凋落叶、土壤C、N、P及化学计量比和养分损失率的影响。研究结果表明：（1）不同大小有效面积林窗下的马尾松凋落叶、土壤C、N、P含量及养分损失率除土壤P含量和马尾松凋落叶P养分损失率外,均存在显著差异。随着林窗有效面积G1~G4的增大,马尾松凋落叶C、N、P含量均呈降低趋势,三者均在G3林窗体现出较小值。马尾松凋落叶C、N、P养分损失率、土壤C、N、P养分含量多呈抛物线趋势,且均在G2或G3林窗体现出最大值。（2）不同大小有效面积林窗下的马尾松凋落叶、土壤C/N/P均存在显著差异。随着林窗有效面积G1~G4的增大,马尾松人工林土壤C/N/P基本呈抛物线变化趋势,土壤C/N在G3林窗出现最大值,土壤C/P、N/P均在G2林窗体现出最大值;土壤C/N、C/P、N/P变异系数分别为13.31%、16.51%、17.21%。马尾松凋落叶C/N、C/P均在G3体现出最小值。（3）马尾松凋落叶C、N含量与土壤C、C/N/P及环境因子的相关性较强,P含量与它们的相关性较弱;C/N与土壤P、C/N/P及环境因子的相关性较强,C/P、N/P与土壤C/P及环境因子的相关性较强;C、N养分损失率与土壤C、C/N、C/P及环境因子的相关性较强,P养分损失率与土壤C、N、P含量及其化学计量比和环境因子的相关性较弱。土壤C、N、P含量及其化学计量比与环境因子的相关性较强。     

Effects of aluminium and micro-nutrients on the sorption of phosphorus byTrifolium repens L. cv. ‘Grasslands Huia’ from nutrient solutions during plant induced pH changes

Summary The sorption of phosphorus from nutrient solution and the pH change in the nutrient solution were monitored over a 24 hour period forTrifolium repens L. cv. ‘Grasslands Huia’ plants. Two different concentration levels of micro-nutrients (B, Cu, Fe, Mn and Zn) and Al formed the factors of a fractional replicate of a 2⁶ factorial design. Measurements were made at four time intervals (30 minutes after the plants were placed on the pots, 3 hours, 6 hours and 24 hours later). In addition to phosphorus, fourteen other nutrients (including nitrate and ammonium) were monitored throughout the experiment. The sorption of phosphorus was significantly influenced by both aluminium and iron. The effect of aluminium and iron on phosphorus sorption is attributed to physico-chemical sorption processes involving the root surface. However the effect on the removal of phosphorus by boron, copper, manganese and zinc was observed only as first order interaction effects —B−Zn, Cu−Zn, Mn−Zn. Thus these three elements (B, Cu and Mn) only affect phosphorus removal in conjunction with zinc. Aluminium and iron together had a separate but very significant effect on the removal of phosphorus at most periods throughout the experiment. In contrast, pH was affected only by aluminium, iron (the pH drop was enhanced) and manganese (the pH drop was decreased) as main effects independent of the other treatment elements.     

Termitaria vs. mistletoe: Effects on soil properties and plant structure in a semi-arid savanna

Termite mounds by creating patches of increased resource availability (e.g. water and nutrients) are a major source of spatial heterogeneity in savannas. Likewise, mistletoes via input of nutrient-rich litter alter nutrient and water availability increasing environmental heterogeneity in semi-arid savanna. Despite this recognition, the influence of termitaria and mistletoe on soil properties and plant community have not been investigated together. We established eight 100 m² plots each on termitaria, under mistletoe-infected trees and in the surrounding savanna and examined the soil properties and the structure of Securinega virosa (Euphorbiaceae) and Euclea divinorum (Ebenaceae) in semi-arid savanna, southwest Zimbabwe. Soil properties significantly differed among the sampling sites (p = 0.001) with soils of increasing clay, soil moisture, pH and phosphorus, calcium and ammonium concentrations occurring on termite mounds. Soils under mistletoe-infected trees were associated with silt, organic matter, sodium, potassium, magnesium and nitrate and the surrounding savanna was associated with soils of increasing sand content. Plant structure also differed significantly between sites with greater basal area of both S. virosa and E. divinorum on termitaria relative to mistletoe-infected trees and the surrounding savanna. However, the stem density of S. virosa was greater under mistletoe-infected trees than on termitaria and in the surrounding savanna. Plant structural variables of individuals of the same species were affected by different soil properties across treatments. The major patterns showed that plant structure was influenced positively by soil moisture and nitrate and negatively by phosphorus on termitaria; positively by clay, soil moisture and ammonium and negatively by potassium under mistletoe-infected trees; and by phosphorus and calcium in the surrounding savanna. These findings show that soil properties, plant structure and their relationships differ between termitaria, mistletoe-infected trees and surrounding savanna, and these differences are suggested to increase heterogeneity in soil resources availability and vegetation structure in semi-arid savanna.     

三峡库区不同林龄马尾松土壤养分与酶活性的关系

基于对三峡库区不同林龄马尾松林下土壤养分和酶活性的测定及典范对应分析,探讨了不同林龄马尾松林土壤养分、酶活性特征及其相互关系.结果表明:马尾松林0 ～ 20 cm土壤有机质、总氮、铵态氮和有效磷含量均表现出成熟林＞中龄林＞近熟林;随着林龄的增加,土壤转化酶活性先降低后增加,纤维素酶、多酚氧化酶活性逐渐降低,而脲酶和过氧化物酶活性先增加后降低.经典范对应分析,不同林分中主要土壤养分对酶活性的影响顺序为总氮＞有机质＞pH＞容重＞铵态氮＞有效磷,转化酶与土壤有机质、总氮、总磷呈显著正相关,过氧化物酶与有机质、总氮、总磷、容重呈显著负相关,土壤主要养分含量高,转化酶活性较高,过氧化物酶活性相对较低.转化酶、纤维素酶和过氧化物酶是评价土壤质量及肥力较好的生物学指标.     

混合生物结皮对土壤养分的影响与群落结构之关联——以黄土丘陵区的生物结皮为例

自然条件下生物结皮是藻、藓及地衣等结皮类型以不同比例组成的混合群落,显著影响土壤养分含量,目前混合生物结皮对土壤养分的影响与其群落结构的关系尚不清楚,限制了混合生物结皮土壤养分的评估。为此,研究通过测定单一组成的藻结皮、藓结皮以及80%藻+20%藓、60%藻+40%藓、40%藻+60%藓和20%藻+80%藓4个不同藻藓比例的混合生物结皮土壤有机碳、全氮、全磷、速效磷、铵态氮和硝态氮含量,研究了混合生物结皮土壤养分与其群落结构之间的关联。结果显示：(1)藓结皮层土壤有机碳、全氮、速效磷、铵态氮和硝态氮含量显著高于藻结皮,分别高出166.4%、77.2%、55.1%、56.2%和42.2%。(2)藻藓混合生物结皮土壤有机碳、全氮、速效磷和铵态氮含量与组成和盖度等结构特征有关,可以通过单一类型生物结皮土壤养分含量与盖度加权预测混合生物结皮土壤养分储量。(3)混合生物结皮土壤有机碳、全氮、速效磷和铵态氮储量实测值(x)与预测值(y)拟合的线性函数分别为y=0.97x、y=0.96x、y=1.18x和y=0.92x。(4)混合生物结皮对全磷和硝态氮含量的影响与群落结构无关。生物结皮对下层0—5 ...     

Environmental Factors Affect Acidobacterial Communities below the Subgroup Level in Grassland and Forest Soils

In soil, Acidobacteria constitute on average 20% of all bacteria, are highly diverse, and are physiologically active in situ. However, their individual functions and interactions with higher taxa in soil are still unknown. Here, potential effects of land use, soil properties, plant diversity, and soil nanofauna on acidobacterial community composition were studied by cultivation-independent methods in grassland and forest soils from three different regions in Germany. The analysis of 16S rRNA gene clone libraries representing all studied soils revealed that grassland soils were dominated by subgroup Gp6 and forest soils by subgroup Gp1 Acidobacteria. The analysis of a large number of sites (n = 57) by 16S rRNA gene fingerprinting methods (terminal restriction fragment length polymorphism [T-RFLP] and denaturing gradient gel electrophoresis [DGGE]) showed that Acidobacteria diversities differed between grassland and forest soils but also among the three different regions. Edaphic properties, such as pH, organic carbon, total nitrogen, C/N ratio, phosphorus, nitrate, ammonium, soil moisture, soil temperature, and soil respiration, had an impact on community composition as assessed by fingerprinting. However, interrelations with environmental parameters among subgroup terminal restriction fragments (T-RFs) differed significantly, e.g., different Gp1 T-RFs correlated positively or negatively with nitrogen content. Novel significant correlations of Acidobacteria subpopulations (i.e., individual populations within subgroups) with soil nanofauna and vascular plant diversity were revealed only by analysis of clone sequences. Thus, for detecting novel interrelations of environmental parameters with Acidobacteria, individual populations within subgroups have to be considered.     

Microscale and Molecular Assessment of Impacts of Nickel, Nutrients, and Oxygen Level on Structure and Function of River Biofilm Communities

Studies were carried out to assess the influence of nutrients, dissolved oxygen (DO) concentration, and nickel (Ni) on river biofilm development, structure, function, and community composition. Biofilms were cultivated in rotating annular reactors with river water at a DO concentration of 0.5 or 7.5 mg liter⁻¹, with or without a combination of carbon, nitrogen, and phosphorus (CNP) and with or without Ni at 0.5 mg liter⁻¹. The effects of Ni were apparent in the elimination of cyanobacterial populations and reduced photosynthetic biomass in the biofilm. Application of lectin-binding analyses indicated changes in exopolymer abundance and a shift in the glycoconjugate makeup of the biofilms, as well as in the response to all treatments. Application of the fluorescent live-dead staining (BacLight Live-Dead staining kit; Molecular Probes, Eugene, Oreg.) indicated an increase in the ratio of live to dead cells under low-oxygen conditions. Nickel treatments had 50 to 75% fewer ‘live’ cells than their corresponding controls. Nickel at 0.5 mg liter⁻¹ corresponding to the industrial release rate concentration for nickel resulted in reductions in carbon utilization spectra relative to control and CNP treatments without nickel. In these cases, the presence of nickel eliminated the positive influence of nutrients on the biofilm. Other culture-dependent analyses (plate counts and most probable number) revealed no significant treatment effect on the biofilm communities. In the presence of CNP and at both DO levels, Ni negatively affected denitrification but had no effect on hexadecane mineralization or sulfate reduction. Analysis of total community DNA indicated abundant eubacterial 16S ribosomal DNA (rDNA), whereas Archaea were not detected. Amplification of the alkB gene indicated a positive effect of CNP and a negative effect of Ni. The nirS gene was not detected in samples treated with Ni at 0.5 mg liter⁻¹, indicating a negative effect on specific populations of bacteria, such as denitrifiers, resulting in a reduction in diversity. Denaturing gradient gel electrophoresis revealed that CNP had a beneficial impact on biofilm bacterial diversity at high DO concentrations, but none at low DO concentrations, and that the negative effect of Ni on diversity was similar at both DO concentrations. Notably, Ni resulted in the appearance of unique bands in 16S rDNA from Ni, DO, and CNP treatments. Sequencing results confirmed that the bands belonged to bacteria originating from freshwater and marine environments or from agricultural soils and industrial effluents. The observations indicate that significant interactions occur between Ni, oxygen, and nutrients and that Ni at 0.5 mg liter⁻¹ may have significant impacts on river microbial community diversity and function.     

The effect of spring water on the growth of a submerged macrophyte Egeria densa

We elucidated the effect of spring water on the growth of Egeria densa Planch., a widespread submerged macrophyte in Japan. We observed the longitudinal distributions of physical (water temperature, particle diameter of the bed sediment, sediment layer thickness, etc.), chemical [pH, dissolved oxygen (DO), dissolved inorganic carbon (DIC), phosphate (PO₄-P), total nitrogen (TN), and total phosphorus (TP) content of the sediment, etc.], and biological (species composition, biomass, and growth rate) factors related to E. densa in the Kurohashi River, a spring-fed stream flowing into the Lake Biwa. It was found that E. densa growth rate from summer to autumn was negatively correlated to pH and DO, which implies that the low pH spring water increases the growth rate of the species. The growth rate was also positively correlated to the free carbon dioxide (CO₂) concentration (r = 0.67, p = 0.02). These results indicate that the low pH spring water increases E. densa growth rate by affecting free CO₂ concentration in water.