microbial ecology Laboratoire de Chrono-environnement UMR UFC/CNRS 6249 USC INRA Université de Franche-Comté, Pôle Universitaire du Pays de Montbéliard 4 place Tharradin, BP 71427 25 211 MONTBELIARD cedex
Abstract: The changes in both physical and chemical properties of interstitial water were investigated within a large gravel bar to determine if the parafluvial zone was a hotspot for nutrient transformations in a lowland eutrophic river, the Doubs (Eastern France). Interstitial water was sampled in 30 piezometers along five transects across the gravel bar, surface water was sampled in main and chute channels. Five campaigns of sampling were performed among summer and winter. In both interstitial and surface samples, water chemistry (electrical conductivity, pH, chloride, dissolved oxygen concentrations-DO) and nutrient concentrations (nitrate-NO3 (-), ammonium-NH4 (+), soluble reactive phosphorus-SRP, dissolved organic carbon-DOC) were measured. Moreover, temperature, water level, sediment grain size distribution and total bacterial abundance were assessed along a flowpath through a lateral gravel bar of the Doubs River. Measurements of water table elevation in the bar, main and chute channels indicated that the parafluvial flowpath was perpendicular to the main channel. Very low changes in chloride concentration and electrical conductivity showed minor groundwater input along the flowpath. The parafluvial zone was 0.9 m thick under the mean piezometric level, hydraulic gradients along the flowpath were 0.3%, and the discharge of interstitial water through the bar calculated at low flow was 40.6 m(3) day(-1). Most changes in interstitial nutrients occurred during the warm season, suggesting that biotic mechanisms occurred. Along the flowpath, DO, DOC, and bacterial abundance declined, while phosphate increased. Temporal trends of nitrate were less clear, exhibiting a slight increase during spring (organic matter biodegradation) and a decrease during summer (denitrification). Using the parafluvial discharge and nutrient concentrations of water infiltrating into and seeping from the gravel bar, the retention capacity of the bar was 171 gC day(-1) for DOC and 48.3 gN day(-1) for nitrate. Phosphate production ranged from 0.65 to 2.3 gP day(-1). These values were low compared to the nutrient fluxes in the river Doubs, suggesting a minimal local impact of the parafluvial zone in regulating of river pollution.
Abstract: 1. While establishment of vegetation is the most visual indicator of regeneration on cutover peatland, the reinstatement of belowground functions is less well understood. Vegetation succession results in differences in peat quality in terms of C availability. The respiratory response of the soil microbial community to ecologically relevant substrates (community-level physiological profile, CLPP) such as those found in rhizosphere exudates and litter hydrolysates, is thought to reflect the activity and functional diversity of the soil microbial community, especially those involved in turnover of soluble photosynthate-derived C. 2. The relationship between CLPP and typical regeneration stages was investigated at five European peatlands, each with up to five sites representing a gradient of natural regeneration stages. We aimed to determine whether unaided revegetation consistently affected soil microbial CLPP, which environmental factors explained variation in CLPP on the scale of individual peatlands, and if these factors were consistent across different peatlands. 3. Within each peatland, a decomposition index based on diagnostic bands in Fourier transform-infrared spectra indicated that regeneration had generally started from a common base and that the influence of vegetation on the decomposition index declined with depth. In parallel, differences in vegetation cover between regeneration stages resulted in significantly different CLPP, but this effect decreased rapidly with soil depth. The magnitudes of the effect of vegetation succession versus soil depth appeared to be linked with the age range of the regeneration gradients. Hence, the effect of vegetation on CLPP is effectively diluted due to the remaining organic matter. Specific plant species described significant proportions of CLPP variability but these species were not consistent across peatland types. The effects of soil depth appeared to be peatland-specific. 4. Synthesis and applications. Together, the results indicate significant responses of the microbial community to vegetation succession, with the strength of the effect probably dependent on quantities of labile C allocation to the soil microbial community. Therefore, particularly in the early stages of regeneration of cutover peatlands, CLPP could provide vital information about the relative importance of different plant functional types on potential rates of labile C turnover.
Abstract: The role of large gravel bars in nutrient retention may vary according to their physical characteristics and their vegetation. The goal of this study was to estimate nutrient fluxes and retention capacity of four gravel bars of a fifth-order river, the Doubs River (Eastern France), during low river discharge in summer and autumn. Patterns of water chemistry, nutrient concentrations, and hydrological characteristics were investigated at -0.3 m depth, using five sampling points in the downwelling zone and five in the upwelling zone of each bar. The dissolved oxygen (DOC) concentrations strongly decreased inside the bars, reaching values below 1 mg L-1 in the upwelling zones in summer, but remained between 1.1 and 4.4 mg L-1 in autumn. Dissolved organic carbon (DOC) concentrations decreased by 21 % to 44 % inside the bars or remained stable (in two bars in autumn). In the upwelling zones they were significantly positively correlated to shrub cover percentage at the bar surface, suggesting a DOC supply by leaf decomposition and root exudates. Nitrate concentrations decreased by 50 % and phosphate increased by 102 % on average along the interstitial flow path in summer, with similar values in the four upwelling zones. Vegetation cover and hydrological characteristics had no significant effect on nitrogen retention nor on phosphorus production. In summer, retention of nitrate and DOC amounted to 16.5 and 25 g day(-1) per 100 m of gravel bar respectively, with differences among bars linked to the intensity of interstitial discharges. Hence, net retention of DOC and NO3- in the parafluvial zone of the Doubs River was relatively high, while release of SRP was low and limited to the summer period.
Abstract: 1. Cut-over peatlands cover large surfaces of high potential value for enhancing biodiversity and carbon sequestration if successfully restored. Unfortunately, evaluation of restoration success is not straightforward. We assessed the bioindicator value of organic matter (OM), testate amoebae (protozoa) and bacteria in peat from two regeneration stages and a reference site of a cut-over bog. 2. Contrasting biochemical signatures of peat OM were observed along the regenerating profiles, allowing clear differentiation between the newly regenerated peat and the old peat. Where peat macrofossils were absent sugar biomarkers were used to infer peat botanical origin and OM alteration. 3. Over the succession, the OM composition of the new peat differed. Peat from the more recent stage was dominated by Sphagnum-derived tissues and characterized by lower carbohydrate preservation and higher bacterial biomass than the advanced regeneration stage. 4. Surface testate amoeba communities also changed from the recent to the advanced stages of regeneration, indicating a shift from wet and moderately acidic conditions to drier and more acidic conditions. Over this regeneration sequence (i) the biomass and average size of species declined but were higher at the unexploited site and (ii) species richness and diversity increased but density declined. 5. Synthesis and applications. Although secondary succession in the cut-over bog led to an ecosystem similar to that of the reference site in terms of surface vegetation, OM and testate amoebae continued to reflect disturbances associated with peat harvesting. Nevertheless, the described dynamics of both microbial and biochemical variables over the succession showed similarities between the advanced stage and the reference site: a higher testate amoeba diversity was associated with better carbohydrate preservation and a more heterogeneous botanical composition of the peat. The inferred water table depth and pH based on testate amoebae indicators proved to be an alternative approach for assessing restoration processes, in contrast to labour-intensive repeated measurements in the field. The botanical and biochemical composition of peat OM provided additional information on past anthropogenic perturbations of the bog and could be used for restoration monitoring. The combination of several indicators therefore provides a more complete assessment of ecological conditions that could be valuable for the management of cut-over peatlands.
Abstract: We studied the effects of lead pollution on testate amoebae communities living on Sphagnum fallax by growing this moss under controlled conditions. A progressive series of lead (Pb) concentration was used in the growing solution of the mosses: 0 (control), 625 and 2500 mu g L-1. The mosses were sampled and analysed for accumulated Pb and testate amoeba communities after 0, 6, 12, and 20 weeks. Species richness, total density and total biomass of testate amoebae declined in response to the Pb treatment and changed over time. The Pb x Time cross-effect was significant for species richness, and total density but not for the total biomass and Shannon diversity. Furthermore, the testate amoebae species richness and the total density were negatively correlated to the Pb concentrations actually accumulated in the moss at the end of the experiment. Species-specific responses of testate amoebae to Pb pollution were identified. Our results thus confirm the sensitivity of testate amoebae to lead pollution. (c) 2007 Elsevier Inc. All rights reserved.
Abstract: We studied the relationships between testate amoeba communities and heavy metal (Pb, Cd, Zn, Ni, Cu, Mn, and Fe) concentrations in the moss Barbula indica sampled at 29 sites in and around the city of Hanoi (Vietnam). Our first approach was to compare the heavy metal concentrations and testate amoeba variables between the city (zone 1) and the surrounding (zone 2). Mean moss concentrations of Pb, Cd, Zn, Ni, and Cu were significantly higher and testate amoeba species richness and abundance were significantly lower in zone 1 and the abundance of eight taxa differed significantly between the two zones. We then studied the correlation between heavy metals and testate amoebae. Species richness and abundance were correlated negatively to Pb concentration. Shannon H' was negatively correlated to both Pb and Cd. The abundance of several species was negatively correlated with Pb, Cd, Zn, and Ni; however, at the community level, Pb emerged as the only significant variable in a redundancy analysis. Our results suggest that testate amoebae are sensitive to and may be good bioindicators for heavy metal pollution, especially lead. Further research is needed to understand the causal relationships underlying the observed patterns.
Abstract: Ecotoxicological studies usually focus on single microbial species under controlled conditions. As a result, little is known about the responses of different microbial functional groups or individual species to stresses. In an aim to assess the response of complex microbial communities to pollution in their natural habitat, we studied the effect of a simulated lead pollution on the microbial community (bacteria, cyanobacteria, protists, fungi, and micrometazoa) living on Sphagnum fallax. Mosses were grown in the laboratory with 0 (control), 625, and 2,500 mu g L-1 of Pb2+ diluted in a standard nutrient solution and were sampled after 0, 6, 12, and 20 weeks. The biomasses of bacteria, microalgae, testate amoebae, and ciliates were dramatically and significantly decreased in both Pb addition treatments after 6, 12, and 20 weeks in comparison with the control. The biomass of cyanobacteria declined after 6 and 12 weeks in the highest Pb treatment. The biomasses of fungi, rotifers, and nematodes decreased along the duration of the experiment but were not significantly affected by lead addition. Consequently, the total microbial biomass was lower for both Pb addition treatments after 12 and 20 weeks than in the controls. The community structure was strongly modified due to changes in the densities of testate amoebae and ciliates, whereas the relative contribution of bacteria to the microbial biomass was stable. Differences in responses among the microbial groups suggest changes in the trophic links among them. The correlation between the biomass of bacteria and that of ciliates or testate amoebae increased with increasing Pb loading. We interpret this result as an effect on the grazing pathways of these predators and by the Pb effect on other potential prey (i.e., smaller protists). The community approach used here complements classical ecotoxicological studies by providing clues to the complex effect of pollutant-affecting organisms both directly and indirectly through trophic effects and could potentially find applications for pollution monitoring.
Abstract: The growth rate and losses of bacterioplankton in the epilimnion of an oligo-mesotrophic reservoir were simultaneously estimated using three different methods for each process. Bacterial production was determined by means of the tritiated thymidine incorporation method, the dialysis bag method and the dilution method, while bacterial mortality was assessed with the dilution method, the disappearance of thymidine-labeled natural cells and ingestion of fluorescent bacterial tracers by heterotrophic flagellates. The different methods used to estimate bacterial growth rates yielded similar results. On the other hand, the mortality rates obtained with the dilution method were significantly lower than those obtained with the use of thymidine-labeled natural cells. The bacterial ingestion rate by flagellates accounted on average for 39% of total bacterial mortality estimated by the dilution method, but this value fell to 5% when the total mortality was measured by the thymidine-labeling method. Bacterial abundance and production varied in opposite phase to flagellate abundance and the various bacterial mortality rates. All this points to the critical importance of methodological aspects in the elaboration of quantitative models of matter and energy flows over the time through microbial trophic networks in aquatic systems, and highlights the role of bacterioplankton as a source of carbon for higher trophic levels in the studied system.
Abstract: Carbon dioxide and methane (CH4) fluxes were measured in a cutover bog of the Jura Mountains (France) together with biotic and abiotic variables for two entire vegetation periods in order to compare the carbon balance of the bog at three stages of regeneration. Among all factors, air temperature and vegetation index (including leaf area of vascular plants, bryophyte density and bryophyte desiccation) were the two main determinants of ecosystem respiration and gross photosynthesis at light saturation. During 2004 and 2005, the vegetated plots acted as carbon sinks. Net carbon exchange ranged between 67 and 166 g C m(-2) yr(-1) for the Eriophorum-dominated plots and between 93 and 183 g C m(-2) yr(-1) for the Sphagnum-dominated plots. The bare peat plots represented a net carbon source (between -19 and -32 g C m(-2) yr(-1)). Methane fluxes accounted for a very small part of the total carbon efflux (< 2%). The recovery of vegetation in our naturally regenerating bog was beneficial for the carbon sequestration after the relatively short period of 20 yr.
Abstract: Previous studies have shown the existence of a vertical micro-distribution of testate amoebae in the first centimeters of Sphagnum and their response to nutrient enrichment. In order to test the response of testate amoebae to depth and N addition in dry moss carpets recolonizing cutover peatlands, we sampled Sphagnum that had received 0, 1, 3, or log N M-2 yr(-1) for three years. The mosses were cut into three segments: 0-1 cm, 1-3 cm and 3-5 cm and analyzed for testate amoebae. The overall diversity (22 taxa) was high considering the dryness of the site, but the species richness of individual samples was low (mean 6.6). The presence of several species characteristic of wetter conditions suggests that they have a broader tolerance than usually believed and/or have a high colonization potential. Species richness increased with depth. Assulina muscorum was most abundant in the top segment, while Phryganella acropodia, Heleopera rosea and Nebela militaris were most abundant in the deepest segment. Neither the metabolism type nor the shell characteristics significantly explained the vertical distribution of species. There was no overall response of testate amoebae to N, although one species, Bullinularia indica, was significantly more abundant in the fertilized than in the control plots.
Abstract: To assess the potential use of testate amoebae as biomonitors of atmospheric pollution we studied the relationship between atmospheric nitrogen dioxide (NO2) pollution and testate amoebae density, diversity, and community structure (Protista: Rhizopoda) in (zone 1) and around (zone 2) the city of Besangon, France. NO2 concentrations were on average significantly lower in the city zone (mean: 34.8 +/- 9.5 mug/m(3)) than in the periphery zone (mean: 14.6 +/- 4.7 mug/m(3)). The density of living amoebae was correlated with that of empty tests (0.001 < p < 0.043 depending on the species), therefore we used the total of dead and living amoebae in all analyses. Testate amoebae species richness was significantly lower in the city (4.7 species) than in the less polluted surrounding areas (6.0 species) but the total density did not vary between the two zones. Of the nine recorded taxa, the density of only one, Paraquadrula irregularis differed significantly between the two zones (p = 0.017), being present in all periphery samples and absent from all city samples. These results are interesting because the pollution level recorded was very low. Although further work is needed before testate amoebae can be used as a monitoring tool for atmospheric pollution, these results suggest they may have a potential for such a use. Further work should focus on potential effects of other pollutants and studies under controlled conditions.
Abstract: Peatlands are ecosystems of exceptional conservation value because of their beauty, biodiversity, importance in global geochemical cycles, and the paleoenvironmental records they preserve. Commercial extraction and drainage for forestry or agriculture have caused the destruction of many peatlands, especially in or close to urban areas of the northern temperate zone. Are these commercial and environmental interests irreconcilable? A close analysis suggests that limited peat extraction may actually increase biodiversity in some cases, and may be sustainable over the long term. As we learn more about how peatlands spontaneously regenerate following disturbance, and what conditions govern the re-establishment of a diverse community and the ability to sequester carbon, we increase our chances of being able to restore damaged peatlands. Preserving the chronological records hidden in the peat profile, the natural heritage value of peatlands, and the bulk of sequestered carbon, however, will remain incompatible with any form of exploitation.
Abstract: Little is known about the structure of microbial communities in Sphagnum peatlands, and the potential effects of the increasing atmospheric CO2 concentration on these communities are not known. We analyzed the structure of microbial communities in five Sphagnum-dominated peatlands across Europe and their response to CO2 enrichment using miniFACE systems. After three growing seasons, Sphagnum samples were analyzed for heterotrophic bacteria, cyanobacteria, microalgae, heterotrophic flagellates, ciliates, testate amoebae, fungi, nematodes, and rotifers. Heterotrophic organisms dominated the microbial communities and together represented 78% to 97% of the total microbial biomass. Testate amoebae dominated the protozoan biomass. A canonical correspondence analysis revealed a significant correlation between the microbial community data and four environmental variables (Na+, DOC, water table depth, and DIN), reflecting continentality, hydrology, and nitrogen deposition gradients. Carbon dioxide enrichment modified the structure of microbial communities, but total microbial biomass was unaffected. The biomass of heterotrophic bacteria increased by 48%, and the biomass of testate amoebae decreased by 13%. These results contrast with the absence of overall effect on methane production or on the vegetation, but are in line with an increased below-ground vascular plant biomass at the same sites. We interpret the increase in bacterial biomass as a response to a CO2-induced enhancement of Sphagnum exudation. The causes for the decrease of testate amoebae are unclear but could indicate a top-down rather than a bottom-up control on their density.
Abstract: In order to yield some insights into the planktonic food web structure of new reservoirs, size-fractionated biomass and productivity of phytoplankton were examined from 1996 to 1997 (following the 1995 flooding of the Sep Reservoir, Puy-de-Dome, France), in relation to nutrients (P, N) and metazooplankton (Rotifers, Cladocera, Copepods). Autotrophic nanoplankton (ANP, size class 3-45 mum) dominated the phytoplankton biomass (as Chlorophyll a) and production, while autotrophic picoplankton (APP, 0.7-3 mum) exhibited the lowest and relatively constant biomass and production. Cells of the autotrophic microplankton (AMP, >45 mum) were considered inedible for planktonic herbivores. The production-biomass diagram for the different size classes and the positive correlation between APP production and ANP + AMP production suggested that grazing was potentially more important than nutrients in shaping the phytoplankton size structure. Metazooplankton biomass was low compared to other newly flooded reservoirs or to natural lakes with phytoplankton biomass similar to that of the Sep Reservoir. This resulted in low ratios (metazooplankton to edible phytoplankton) both in terms of production (average 0.43% in 1996 and 0.76% in 1997) and biomass, suggesting that only a small fraction of phytoplankton was directly consumed by metazooplankton. We suggest that the observed low ratios in the Sep Reservoir, reflect possible low metazooplankton inputs in the main influents, changes in hydrologic conditions and a high potential role of microheterotrophs. The latter role was supported by (i) the positive inter-annual correlation between ciliates and phytoplankton, (ii) the significant and negative correlations between ciliates and metazooplankton, and (iii) the significant and negative correlations between total metazooplankton biomass and total phosphorus (TP), whereas neither TP nor total metazooplankton biomass was correlated with phytoplankton variables.
Abstract: Population dynamics and food preferences of the testate amoeba species complex Nebela tincta major-bohemica-collaris ("Nebela collaris sensu lato") were described from a Sphagnum peatland over one growing season. The average abundance of Nebela collaris sensu lato was 29582 ind. 1(-1) active, and 2263 ind. 1(-1) encysted forms. On average, 17.4% of Nebela collaris sensu lato specimens were observed associated with prey, 71% of which could not be identified because of their poor preservation state. Among the identified prey, those most frequently ingested were micro-algae (45% of the total predator-prey associations, especially diatoms: 33%), and spores and mycelia of fungi (36%). Large ciliates, rotifers and small testate amoebae were also ingested, but mainly in summer. The seasonal variations in the proportions of prey categories in the ecosystem and the percentage of identifiable prey lead us to hypothesise that (1) Nebela collaris sensu lato ingest mainly immobile, senescent or dead organisms, and (2) that the more mobile micro-organisms such as ciliates and micro-Metazoa become more accessible, in relatively dry conditions, when the water film is thin.
Abstract: To monitor global change, large scale long term studies are needed. Such studies often focus on vegetation, but most plant species have limited distribution areas. Micro-organisms by contrast are mostly cosmopolitan in their distributions. To study the relationships between organisation groups, we analysed the testate amoebae (Protozoa), vegetation, and water chemistry of five Sphagnum peatlands across Europe. Inter-site differences were more pronounced for the vegetation than for testate amoebae species assemblage. Testate amoebae represent a useful tool in multi-site studies and environmental monitoring of peatlands because: 1) the number of species is much higher than for plants, 2) most species are cosmopolitan and are therefore less affected by biogeographical distribution patterns than plants; thus differences in restate amoebae assemblages can be interpreted primarily in terms of ecology, 3) restate amoebae can be used to analyse and monitor small scale (cm) gradients that play a major role in the functioning of peatland ecosystems. We further studied the effect of elevated CO2 on microbial communities in the same peatlands. Elevated COL increased the biomass of heterotrophic bacteria and decreased the biomass of medium size protozoa (mostly small restate amoebae). These effects suggest changes in community functioning that may have feedback effects on other components of the ecosystem.
Abstract: Tcslate amoeba are a heterogeneous and most likely polyphyletic group of free-living protists. Their common characteristic is the presence of a test. Testate amoebae have been observed in almost every aqualic habitat, mainly in the periphytic zone of fresh and salt water bodies, soils and mosses. These protozoa are of great interest in the study of ecosystems. Indeed, the presence of a rigid test makes their identification relatively easy and they are good biological indicators. Furthermore, these micro-organisms play a key role in the structure and the functioning of microbial communities at the surface of Sphagnum peatlands. Nevertheless, testate amoebae remain globally little studied. More precisely, only limited data exist on their feeding habits although this is a necessary preliminary key aspect to understand their role in microbiai trophic networks. The aim of this review therefore is to allow a synthesis of the observations at hand in the literature on the feeding behaviour of testate amoebae. An important part of this review is devoted to our own observations on the species living in Sphagnum. Although testate amoebae arc generally believed to be heterotrophic. several species arc mixotrophic. Strict heterotrophy however remains the dominant trophic mode of testate amoebae. In the literature, several authors consider testate amoebae as largely bacterivorous. It seems however that many species ingest other kinds of prey: paniculate organic matter, microalgae, plant cells, prolists, fungi and small metazoa. Furthermore, some species are polyphagous while others seem to have more specialised feeding habits. Little is known on prey identification by testate amoebae. In particular, it is difficult to tell if mechanisms of distant detection (e.g. chimiotactism) exist or if a physical contact is necessary. Our observations on living and on fixed individuals suggest that both mechanisms exist. Furthermore, it seems that the food selectivity by testate amoebae is influenced by the physiological state of prey organisms at the moment of their ingestion. As for naked amoebae, the ingestion of prey is done by invagination of the cytoplasmic membrane. However, the particularity of testate amoebae is that the ingestion and egestion lake place at the level of the pseudostome. but no clearly defined cytostome or cytoprocte exist. The ability of some testate amoebae species to ingest a wide range of prey sizes (0,2 to 1 000 μm) and of very different kinds likely represents an competitive advantage in some environments. In these conditions, it seems important to improve our knowledge on the biology and the ecology of these protozoa.
Abstract: The distribution of soil microorganisms is generally believed to be patchy and to reflect habitat heterogeneity. Despite this general rule, the amount of existing data oil species distribution patterns is scarce. Testate amoebae (Protozoa; Rhizopoda) are an important component of soil microbial communities and are increasingly used in ecological and paleoecological studies of Sphagnum-dominated peatlands, but data on the spatial structure of communities are completely lacking. This is an important aspect since quantitative models used for paleoecological reconstruction and monitoring are based on species assemblages. We explored the distribution patterns of testate amoebae distribution in a macroscopically homogeneous Sphagnum carpet, down to a scale of several centimeters. Distributions maps of the species and spatially constrained sample groups were produced. Multivariate and individual spatial autocorrelations were calculated. The importance of spatial structure was quantified by canonical correspondence analysis. Our ultimate goal is to find the finest resolution of environmental monitoring using testate amoebae. The distribution patterns differed among species, resulting in a complex spatial structure of the species assemblage in a whole. Spatial structure accounted for 36% of the total variation of species abundance in a canonical correspondence analysis constrained by spatial variables. This structure was partly correlated to altitude (microtopography) at a very fine scale. These results confirmed the existence of significant broad-and fine-scale spatial structures within restate amoebae communities that could in parr be interpreted as effects of ecological gradients. This shows that, on a surface area of 0.25 m(2), ecological conditions which look uniform from a macroscopic point of view are not perceived as such by Sphagnum-inhabiting organisms. Therefore, restate amoebae could prove very useful to monitor fine-scale ecological processes or disturbances. Studies of the species' spatial distribution patterns in combination with autoecological studies are needed and should be included in the toolbox of biomonitoring itself.
Abstract: Nitrogen additions as NH4NO3 corresponding to 0 (N0), 1 (N1), 3 (N3) and 10 (N10) g N m(-2) yr(-1) were made to Sphagnum magellanicum cores at two-week intervals in situ at four sites across Europe, i.e. Lakkasuo (Finland), Mannikjarve (Estonia), Moidach More (UK) and Cote de Braveix (France). The same treatments were applied in a glasshouse experiment in Neuchatel (Switzerland) in which the water table depth was artificially maintained at 7, 17 and 37 cm below the moss surface. In the held, N assimilation in excess of values in wet deposition occurred in the absence of growth, but varied widely between sites, being absent in Lakkasuo (moss N:P ratio 68) and greatest in Moidach More (N:P 21). In the glasshouse, growth was reduced by lowering the water table without any apparent effect on N assimilation. Total N content of the moss in field sites increased as the mean depth of water table increased indicating growth limitation leading to increased N concentrations which could reduce the capacity for N retention. Greater contents of NH4+ in the underlying peat at 30 cm depth, both in response to NH4NO3 addition and in the unamended cores confirmed poor retention of inorganic N by the moss at Lakkasuo. Nitrate contents in the profiles at Lakkasuo, Moidach More, and Cote de Braveix were extremely low, even in the N10 treatment, but in Mannikjarve, where the mean depth of water table was greatest and retention absent, appreciable amounts of NO3- were detected in all cores. It is concluded that peatland drainage would reduce the capture of inorganic N in atmospheric deposition by Sphagnum mosses.
Abstract: The aim of this study was to assess the structure and function of the microbial loop in a peatland of the French Massif central, and the impact of fertilization on the different microbial communities. In terms of biomass, testate Amoeba (48% of the total microbial biomass), heterotrophic bacteria (15%), cyanobacteria (14%) and Bacillariophyceae (13%) were the dominant groups of microorganisms. Other microalgae (7%), ciliates (2%) and heterotrophic flagellates (1%) accounted for only a low proportion of total microbial biomass. The relative importance of heterotrophic microorganisms was higher than in marine or lacustrine environments. In addition, ciliates and heterotrophic flagellates only constituted a small proportion of the total protozoan biomass, which was heavily dominated by testate amoeba. Thus, the structure of the protist community in the subaquatic peatland was completely different from that reported for lakes or marine environments. In other aspects, the supply of nutrients (PKCa and NPKCa) resulted in increases of the relative biomasses of heterotrophic bacteria, Bacillariophyceae, and ciliates and by a decrease in the relative proportion of testate amoeba and of other microalgae.
Abstract: The aim of this study was to assess the structure of the microbial loop in a Sphagnum fallax - Carer rostrata fen of the French Massif central, and the impact of nitrogen supplies on the different microbial communities. Microalgae (46% of the total microbial biomass), Protozoa (26%) and heterotrophic Bacteria (17%) were the dominant microorganisms. Rotifera (5%), Cyanobacteria (3%), Fungi (2%) and Nematoda (< 1%) were also present. Testate Amoebae were well represented in Sphagnum peatland (14% of total microbial biomass). Thus, the structure of the protist community in the surface of fen peatlands is notably different from that recorded in other environments. The input of nitrogen led to a steady increase in microbial biomasses, but only changed the structure of microbial communities significantly when the input was 50 kg ha(-1). At high inputs, nitrogen supply increased the relative importance of Cyanobacteria, Euglenophyceae, Bacillariophyceae and Ciliates, and decreased the relative importance of heterotrophic Bacteria, other microalgae and testate Amoebae. The increase in the values of photosynthetic assimilation and heterotrophic activities could also reflect changes in community functioning.
Abstract: The locality of Chilhac (Haute-Loire, France) has yielded an abundant fauna of vertebrate (fifteen fossil mammal species and three fossil bird species). The existence of plant prints were revealed lately, they concern endocarp prints of the genus: Prunus. Recently, the discovery of smaller splinters of parts of the plant, which were moulded by volcanic ash, were studied by scanning electron microscopy. They show, for the first time in Upper-Pliocene, the presence of Testate Ameobae of the genus Trinema.
