Microcosm Experiments (microcosm + experiment)

Distribution by Scientific Domains

Selected Abstracts

Low temperature bioremediation of oil-contaminated soil using biostimulation and bioaugmentation with a Pseudomonas sp. from maritime Antarctica

B. Stallwood
Abstract Aims:, To identify native Antarctic bacteria capable of oil degradation at low temperatures. Methods and Results:, Oil contaminated and pristine soils from Signy Island (South Orkney Islands, Antarctica) were examined for bacteria capable of oil degradation at low temperatures. Of the 300 isolates cultured, Pseudomonas strain ST41 grew on the widest range of hydrocarbons at 4°C. ST41 was used in microcosm studies of low temperature bioremediation of oil-contaminated soils. Microcosm experiments showed that at 4°C the levels of oil degradation increased, relative to the controls, with (i) the addition of ST41 to the existing soil microbial population (bioaugmentation), (ii) the addition of nutrients (biostimulation) and to the greatest extent with (iii) a combination of both treatments (bioaugmentation and biostimulation). Addition of water to oil contaminated soil (hydration) also enhanced oil degradation, although less than the other treatments. Analysis of the dominant species in the microcosms after 12 weeks, using temporal temperature gradient gel electrophoresis, showed Pseudomonas species to be the dominant soil bacteria in both bioaugmented and biostimulated microcosms. Conclusions:, Addition of water and nutrients may enhance oil degradation through the biostimulation of indigenous oil-degrading microbial populations within the soil. However, bioaugmentation with Antarctic bacteria capable of efficient low temperature hydrocarbon degradation may enhance the rate of bioremediation if applied soon after the spill. Significance and Impact of the Study:, In the future, native soil bacteria could be of use in bioremediation technologies in Antarctica. [source]

Remobilization of Polychlorinated Biphenyl from Baltic Sea Sediment: Comparing the Roles of Bioturbation and Physical Resuspension

Jenny E. Hedman
Abstract The release of a 14C-labeled trichlorobiphenyl compound ([14C]PCB 32) from sediment to water was quantified weekly in a 30-d microcosm experiment with recirculating water. Two modes of bioturbation-driven polychlorinated biphenyl (PCB) release,bioturbation by the amphipod Monoporeia affinis (a particle biodiffuser) and bioturbation by the polychaete Marenzelleria sp. (a bioirrigator),were compared to the PCB release caused by physical resuspension of the sediment generated by a motor-driven paddle used twice a week. Bioturbation by the amphipod M. affinis caused a significantly higher remobilization of both particle-associated PCB (PCBpart) and dissolved PCB (PCBdiss) than the other treatments. Bioturbation by Marenzelleria sp. and physical resuspension caused a similar release of PCBdiss despite a significantly higher amount of total suspended solids in the water column after physical resuspension. In all treatments, the release of PCBdiss was more than one order of magnitude higher than that of PCBpart, indicating a significant potential route of exposure for pelagic organisms, such as fish, to the most bioavailable PCB form. Calculated mass-transfer coefficients (0.3,1.3 cm/d) correspond to previously reported values for trichlorinated PCBs. The present results indicate that biological reworking of sediments can be just as, or even more, important than physical resuspension for the remobilization of sediment-bound contaminants. [source]

Kinetics of cadmium accumulation in periphyton under freshwater conditions,

Philippe Bradac
Abstract The aim of the present study was to investigate the kinetics of cadmium (Cd) accumulation (total and intracellular) in periphyton under freshwater conditions in a short-term microcosm experiment. Periphyton was precolonized in artificial flow-through channels supplied with natural freshwater and then exposed for 26.4 h to nominal Cd concentrations of 5 and 20 nM added to natural freshwater. Labile Cd in water determined with diffusion gradient in thin films was 60 to 69% of total dissolved Cd in the exposure channels and 11% in the control channel. Intracellular Cd concentrations in periphyton increased rapidly and linearly during the first 71 min. Initial intracellular uptake rates were 0.05 and 0.18 nmol of Cd/g of dry weight × min in the 5 nM and 20 nM exposures, respectively. The subsequent intracellular uptake was slower, approaching steady state at the end of Cd exposure. Uptake kinetics of Cd was slower when compared to experiments with planktonic algal cultures, probably due to diffusion limitations. Intracellular Cd uptake during the entire exposure was modeled with a nonlinear, one-compartment model from which uptake and clearance rate constants, as well as bioconcentration factors, were obtained. The release of Cd from periphyton after the end of Cd exposure was slow when compared to the initial uptake rates. [source]

Transfer of Cd, Cu, Ni, Pb, and Zn in a soil-plant-invertebrate food chain: A microcosm study,

Renaud Scheifler
Abstract The transfer of Cd, Cu, Ni, Pb, and Zn was evaluated in a soil-plant (lettuce, Lactuca sativa),invertebrate (snail, Helix aspersa) food chain during a microcosm experiment. Two agricultural soils, polluted and unpolluted, were studied. Lettuce was cultivated for eight weeks before introduction of snails into the microcosms (M-snails). In a parallel experiment, snails were exposed to lettuce only (i.e., without soil) in simpler exposure devices called containers (C-snails). Snail exposure duration was eight weeks for both M- and C-snails. No effects on snail survival were found. Both M- and C-snails exposed to polluted soil showed a growth reduction, but only after two weeks of exposure. Time-dependent accumulation in M-snails exposed to the polluted environment showed a regular increase of Cd and Zn concentrations over time and a rapid increase of Pb concentrations within the first two weeks, which then remained stable. Copper and Ni concentrations did not increase during any of the experiments. Concentrations in M- and C-snails were compared to estimate the relative contribution of soil and plant to the total bioaccumulation. The results suggest that the soil contribution may be higher than 80% for Pb, from 30 to 60% for Zn, and from 2 to 40% for Cd. [source]

Effects of long-chain hydrocarbon-polluted sediment on freshwater macroinvertebrates

Vincent Pettigrove
Abstract High-molecular weight (>C16) hydrocarbons (HMWHs) are common pollutants in sediments of freshwater systems, particularly urban water bodies. No sediment quality guidelines exist for total hydrocarbons; more emphasis is placed on polyaromatic hydrocarbons, the most toxic component of hydrocarbons. A field-based microcosm experiment was conducted to determine whether unpolluted sediments spiked with synthetic motor oil impair freshwater macroinvertebrate assemblages. Total petroleum hydrocarbon (TPH) concentrations of 860 mg/kg dry weight significantly increased the abundance of Polypedilum vespertinus and Cricotopus albitarsis and decreased the abundance of Paratanytarsus grimmii adults (all Chironomidae), whereas TPH concentrations ranging from 1,858 to 14,266 mg/kg produced a significant reduction in the total numbers of taxa and abundance, with significant declines in the abundance of nine chironomid taxa. About 28% of water bodies surveyed in urban Melbourne, Australia, had TPH concentrations in sediments likely to cause ecological impairment, and about 14% of the water bodies surveyed are likely to have reduced species richness and abundance. Therefore, HMWHs can be a significant pollutant in urban water bodies. Freshwater sediment quality guidelines should be developed for this ubiquitous urban pollutant. [source]

Allelopathic effect of the aquatic macrophyte, Stratiotes aloides, on natural phytoplankton

Summary 1. A survey of different Dutch Stratiotes stands showed that the density of phytoplankton (except cyanobacteria) was always higher outside S. aloides than between the rosettes of S. aloides. Analyses of water samples revealed that nutrient limitation was unlikely to have caused the lower phytoplankton biomass in the vicinity of S. aloides. 2. An in situ incubation experiment in the Danube Delta, Romania, indicated allelopathic activity against phytoplankton in S. aloides stands. The growth rate of natural phytoplankton populations exposed to water from S. aloides stands was significantly lower than that of populations that had not been in contact with S. aloides exudates. 3. A laboratory microcosm experiment showed a significantly lower phytoplankton biomass in treatments with S. aloides exudates. Nutrient concentrations and the light intensity were high enough that the lower phytoplankton biomass could not be explained by nutrient or light limitation. [source]

Soil animals influence microbial abundance, but not plant,microbial competition for soil organic nitrogen

Summary 1In a microcosm experiment we examined the effects of individual species of microarthropods, and variations in microarthropod diversity of up to eight species, on soil microbial properties and the short-term partitioning of a dual-labelled organic nitrogen source (glycine-2- 13C- 15N) between a grassland plant, Agrostis capillaris, and the soil microbial biomass, to determine how soil fauna and their diversity influence plant,microbial competition for organic N. 2We hypothesized that variations in the diversity of animals would influence the partitioning of 15N inputs between plants and the microbial biomass, due to the effect of animal grazing on the microbial biomass, and hence its ability to sequester N. 3Certain individual species of Collembola influenced the microbial community of the soil. Folsomia quadrioculata reduced microbial biomass, whereas Mesaphorura macrochaeta enhanced arbuscular mycorrhizal (AM) colonization of A. capillaris roots. Effects of increasing species richness of microarthropods on microbial biomass and AM colonization were detected, but these effects could be interpreted in relation to the presence or absence of individual species. 4Microbial uptake of added 15N was not affected by the presence of any of the individual species of animal in the monoculture treatments. Similarly, increasing diversity of microarthropods had no detectable effect on microbial 15N. 5Root and shoot uptake of 15N was also largely unaffected by both single species and variations in diversity of microarthropods. However, one collembolan species, Ceratophysella denticulata, reduced root 15N capture when present in monoculture. We did not detect 13C in plant tissue under any experimental treatments, indicating that all N was taken up by plants after mineralization. 6Our data suggest that, while single species and variations in diversity of microarthropods influence microbial abundance in soil, there is no effect on microbial or plant uptake of N. Overall, these data provide little support for the notion that microbial-feeding soil animals are regulators of microbial,plant competition for N. [source]

Magnitude and variability of process rates in fungal diversity-litter decomposition relationships

ECOLOGY LETTERS, Issue 11 2005
Christian K. Dang
Abstract There is compelling evidence that losses in plant diversity can alter ecosystem functioning, particularly by reducing primary production. However, impacts of biodiversity loss on decomposition, the complementary process in the carbon cycle, are highly uncertain. By manipulating fungal decomposer diversity in stream microcosm experiments we found that rates of litter decomposition and associated fungal spore production are unaffected by changes in decomposer diversity under benign and harsher environmental conditions. This result calls for caution when generalizing outcomes of biodiversity experiments across systems. In contrast to their magnitude, the variability of process rates among communities increased when species numbers were reduced. This was most likely caused by a portfolio effect (i.e. statistical averaging), with the uneven species distribution typical of natural communities tending to weaken that effect. Curbing species extinctions to maintain ecosystem functioning thus can be important even in situations where process rates are unaffected. [source]

Perpest model, a case-based reasoning approach to predict ecological risks of pesticides

Paul J. Van den Brink
Abstract The PERPEST model is a model that predicts the ecological risks of pesticides in freshwater ecosystems. This model simultaneously predicts the effects of a particular concentration of a pesticide on various (community) endpoints. In contrast to most effect models, PERPEST is based on empirical data extracted from the literature. This model is based on case-based reasoning, a technique that solves new problems (e.g., what is the effect of pesticide A?) by using past experience (e.g., published microcosm experiments). The database containing the past experience has been constructed by performing a review of freshwater model ecosystem studies. This review assessed the effects on various endpoints (e.g., community metabolism, phytoplankton, and macroinvertebrates) and classified them according to their magnitude and duration. The PERPEST model searches for analogous situations in the database, based on relevant (toxicity) characteristics of the compound. This allows the model to predict effects of pesticides for which no effects on a semifield scale have been published. The PERPEST model results in a prediction showing the probability of classes of effects (no, slight, or clear effects, plus an optional indication of recovery) on the various grouped endpoints. This paper discusses the scientific background of the model as well as its strengths, limitations, and possible applications. [source]

A test of the community conditioning hypothesis: Persistence of effects in model ecological structures dosed with the jet fuel jp-8

Wayne G. Landis
Abstract The foundation of the community conditioning hypothesis, the persistence of effects, was tested in a series of microcosm experiments. Experiments were conducted with the water-soluble fraction of the turbine fuel JP-8 using the standard protocols for the standardized aquatic microcosm (SAM). A repeat trial was conducted using the SAM protocol but with a 126-d test period, twice the standard duration. The results were examined using a variety of conventional univariate, multivariate, and graphical techniques. The principal conclusions were as follows. Effects are persistent in these model ecological systems long after the degradation of the toxicant. Patterns of impacts are detectable at concentrations 15 times lower than an experimentally derived single-species EC50. The replicate experiments are not replicable in the specific, but the broad pattern of the disruption of algal- herbivore dynamics followed by more subtle effects are consistently repeated. The durability of the indirect effects and therefore the information about historical events appears to be a consistent feature of these microcosm systems. The identity of the treatment groups persists. The critical features of the community conditioning hypothesis,persistence of information within ecologicalsystems and the reappearance of patterns and therefore the nonequilibrium dynamics,are again confirmed. The implications of these findings for environmental toxicology, monitoring, and ecological risk assessment are discussed. [source]

On the reproducibility of microcosm experiments , different community composition in parallel phototrophic biofilm microcosms

Guus Roeselers
Abstract Phototrophic biofilms were cultivated simultaneously using the same inoculum in three identical flow-lane microcosms located in different laboratories. The growth rates of the biofilms were similar in the different microcosms, but denaturing gradient gel electrophoresis (DGGE) analysis of both 16S and 18S rRNA gene fragments showed that the communities developed differently in terms of species richness and community composition. One microcosm was dominated by Microcoleus and Phormidium species, the second microcosm was dominated by Synechocystis and Phormidium species, and the third microcosm was dominated by Microcoleus- and Planktothrix -affiliated species. No clear effect of light intensity on the cyanobacterial community composition was observed. In addition, DGGE profiles obtained from the cultivated biofilms showed a low resemblance with the profiles derived from the inoculum. These findings demonstrate that validation of reproducibility is essential for the use of microcosm systems in microbial ecology studies. [source]

Nutrient cycling efficiency explains the long-term effect of ecosystem engineers on primary production

Summary 1Soil organisms, such as earthworms, accelerate mineralization of soil organic matter and are thought to be beneficial for plant growth. This has been shown in short-term microcosm experiments. It is thus legitimate to ask whether these increases in plant growth are due to brief pulses of mineralization or whether these increases are long-lasting. 2This question was addressed using a system of differential equations modelling the effects of decomposers on nutrient cycling via trophic (nutrient assimilation) and nontrophic effects (through their ecosystem engineering activities). 3The analytical study of this model showed that these processes increase primary production in the long term when they recycle nutrients efficiently, allowing a small fraction of the recycled nutrients to be leached out of the ecosystem. 4Mineralization by the ecosystem engineering activities of decomposers seems to deprive them of a resource. However, it was shown that a decomposer may increase its own biomass, through its ecosystem engineering activities, provided the created recycling loop is efficient enough. 5Mechanisms through which earthworms may modify the efficiency of nutrient cycling are discussed. The necessity of measuring the effect of earthworms on the nutrient input,output balance of ecosystems under field conditions is emphasized. [source]

Plant nitrogen acquisition and interactions under elevated carbon dioxide: impact of endophytes and mycorrhizae

Abstract Both endophytic and mycorrhizal fungi interact with plants to form symbiosis in which the fungal partners rely on, and sometimes compete for, carbon (C) sources from their hosts. Changes in photosynthesis in host plants caused by atmospheric carbon dioxide (CO2) enrichment may, therefore, influence those mutualistic interactions, potentially modifying plant nutrient acquisition and interactions with other coexisting plant species. However, few studies have so far examined the interactive controls of endophytes and mycorrhizae over plant responses to atmospheric CO2 enrichment. Using Festuca arundinacea Schreb and Plantago lanceolata L. as model plants, we examined the effects of elevated CO2 on mycorrhizae and endophyte (Neotyphodium coenophialum) and plant nitrogen (N) acquisition in two microcosm experiments, and determined whether and how mycorrhizae and endophytes mediate interactions between their host plant species. Endophyte-free and endophyte-infected F. arundinacea varieties, P. lanceolata L., and their combination with or without mycorrhizal inocula were grown under ambient (400 ,mol mol,1) and elevated CO2 (ambient + 330 ,mol mol,1). A 15N isotope tracer was used to quantify the mycorrhiza-mediated plant acquisition of N from soil. Elevated CO2 stimulated the growth of P. lanceolata greater than F. arundinacea, increasing the shoot biomass ratio of P. lanceolata to F. arundinacea in all the mixtures. Elevated CO2 also increased mycorrhizal root colonization of P. lanceolata, but had no impact on that of F. arundinacea. Mycorrhizae increased the shoot biomass ratio of P. lanceolata to F. arundinacea under elevated CO2. In the absence of endophytes, both elevated CO2 and mycorrhizae enhanced 15N and total N uptake of P. lanceolata but had either no or even negative effects on N acquisition of F. arundinacea, altering N distribution between these two species in the mixture. The presence of endophytes in F. arundinacea, however, reduced the CO2 effect on N acquisition in P. lanceolata, although it did not affect growth responses of their host plants to elevated CO2. These results suggest that mycorrhizal fungi and endophytes might interactively affect the responses of their host plants and their coexisting species to elevated CO2. [source]

Plant and microbial N acquisition under elevated atmospheric CO2 in two mesocosm experiments with annual grasses

Shuijin Hu
Abstract The impact of elevated CO2 on terrestrial ecosystem C balance, both in sign or magnitude, is not clear because the resulting alterations in C input, plant nutrient demand and water use efficiency often have contrasting impacts on microbial decomposition processes. One major source of uncertainty stems from the impact of elevated CO2 on N availability to plants and microbes. We examined the effects of atmospheric CO2 enrichment (ambient+370 ,mol mol,1) on plant and microbial N acquisition in two different mesocosm experiments, using model plant species of annual grasses of Avena barbata and A. fatua, respectively. The A. barbata experiment was conducted in a N-poor sandy loam and the A. fatua experiment was on a N-rich clayey loam. Plant,microbial N partitioning was examined through determining the distribution of a 15N tracer. In the A. barbata experiment, 15N tracer was introduced to a field labeling experiment in the previous year so that 15N predominantly existed in nonextractable soil pools. In the A. fatua experiment, 15N was introduced in a mineral solution [(15NH4)2SO4 solution] during the growing season of A. fatua. Results of both N budget and 15N tracer analyses indicated that elevated CO2 increased plant N acquisition from the soil. In the A. barbata experiment, elevated CO2 increased plant biomass N by ca. 10% but there was no corresponding decrease in soil extractable N, suggesting that plants might have obtained N from the nonextractable organic N pool because of enhanced microbial activity. In the A. fatua experiment, however, the CO2 -led increase in plant biomass N was statistically equal to the reduction in soil extractable N. Although atmospheric CO2 enrichment enhanced microbial biomass C under A. barbata or microbial activity (respiration) under A. fatua, it had no significant effect on microbial biomass N in either experiment. Elevated CO2 increased the colonization of A. fatua roots by arbuscular mycorrhizal fungi, which coincided with the enhancement of plant competitiveness for soluble soil N. Together, these results suggest that elevated CO2 may tighten N cycling through facilitating plant N acquisition. However, it is unknown to what degree results from these short-term microcosm experiments can be extrapolated to field conditions. Long-term studies in less-disturbed soils are needed to determine whether CO2 -enhancement of plant N acquisition can significantly relieve N limitation over plant growth in an elevated CO2 environment. [source]

Extremely Alkaline (pH > 12) Ground Water Hosts Diverse Microbial Community

GROUND WATER, Issue 4 2006
George S. Roadcap
Chemically unusual ground water can provide an environment for novel communities of bacteria to develop. Here, we describe a diverse microbial community that inhabits extremely alkaline (pH > 12) ground water from the Lake Calumet area of Chicago, Illinois, where historic dumping of steel slag has filled in a wetland. Using microbial 16S ribosomal ribonucleic acid gene sequencing and microcosm experiments, we confirmed the presence and growth of a variety of alkaliphilic ,-Proteobacteria, Bacillus, and Clostridium species at pH up to 13.2. Many of the bacterial sequences most closely matched those of other alkaliphiles found in more moderately alkaline water around the world. Oxidation of dihydrogen produced by reaction of water with steel slag is likely a primary energy source to the community. The widespread occurrence of iron-oxidizing bacteria suggests that reduced iron serves as an additional energy source. These results extend upward the known range of pH tolerance for a microbial community by as much as 2 pH units. The community may provide a source of novel microbes and enzymes that can be exploited under alkaline conditions. [source]

Ecosystem functioning in stream assemblages from different regions: contrasting responses to variation in detritivore richness, evenness and density

B. G. McKie
Summary 1The diversity of species traits in a biological assemblage varies not only with species richness, but also with species evenness and organism density, which together influence the concentration of traits within functional guilds. Potential trait diversity at local scales is also constrained by the regional species pool. Implications of such variation for spatio-temporal variability in biodiversity,ecosystem functioning relationships are likely to be complex, but are poorly understood. 2In microcosm experiments conducted at laboratories in Sweden, Ireland and Romania, we investigated effects of species richness, evenness and density of stream-living detritivores on two related processes: detritivore leaf-processing efficiency (LPE) and growth. Assemblage composition varied among laboratories: one taxonomic order (Plecoptera) was studied in Sweden, whereas two orders, encompassing wider trait variation, were studied in Romania (Trichoptera and Plecoptera) and Ireland (Trichoptera and Isopoda). 3Relationships between density and both LPE and growth ranged from negative to positive across the study species, highlighting the potential for density-dependent variation in process rates to alter ecosystem functioning, but indicating that such effects depend on species identity. 4LPE varied with species diversity in the two more heterogeneous assemblages, but whereas LPE in the Romanian study was generally enhanced as richness increased, LPE in the Irish study increased only in less-even polycultures dominated by particular species. Transgressive overyielding was detected in the Irish experiment, indicating complementary resource use and/or facilitation (complementarity). These mechanisms could not be distinguished from the selection effect in the Romanian study. 5Growth was elevated in Romanian species mixtures, reflecting positive complementarity, but lower than expected growth in some Swedish mixtures was associated with negative complementarity, indicating interspecific interference competition. 6Our results emphasize the potential importance of detritivore diversity for stream ecosystem functioning, but both the effects of diversity on the studied processes, and the mechanisms underlying those effects, were specific to each assemblage and process. Such variability highlights challenges in generalizing impacts of diversity change for functional integrity in streams and other ecosystems in which the occurrence of important species traits fluctuates over relatively small spatio-temporal scales. [source]

Prey diversity, prey composition, and predator population dynamics in experimental microcosms

Owen L. Petchey
Summary 1. Food-web complexity-stability relations are central to ecology, and many empirical studies show greater food-web complexity leads to lower population stability. Here, predator population variability decreased with increasing prey diversity in aquatic microcosm experiments, an example of greater food-web complexity leading to greater population stability. 2. Prey diversity as well as different sets of prey species within each level of prey diversity produced differences in predator population dynamics, demonstrating the importance of both prey composition and prey diversity in determining predator population stability. 3. Prey diversity can affect predator population dynamics through at least three groups of mechanisms: prey reliability, prey biomass, and prey composition mechanisms. The results suggest that greater prey reliability at higher prey diversities enhances predator stability and provide support for MacArthur (1955). [source]

Mixed aerobic and anaerobic microbial communities in benzene-contaminated groundwater

A. Aburto
Abstract Aims:, To investigate the factors affecting benzene biodegradation and microbial community composition in a contaminated aquifer. Methods and Results:, We identified the microbial community in groundwater samples from a benzene-contaminated aquifer situated below a petrochemical plant. Eleven out of twelve groundwater samples with in situ dissolved oxygen concentrations between 0 and 2·57 mg l,1 showed benzene degradation in aerobic microcosm experiments, whereas no degradation in anaerobic microcosms was observed. The lack of aerobic degradation in the remaining microcosm could be attributed to a pH of 12·1. Three groundwaters, examined by 16S rRNA gene clone libraries, with low in situ oxygen concentrations and high benzene levels, each had a different dominant aerobic (or denitrifying) population, either Pseudomonas, Polaromonas or Acidovorax species. These groundwaters also had syntrophic organisms, and aceticlastic methanogens were detected in two samples. The alkaline groundwater was dominated by organisms closely related to Hydrogenophaga. Conclusions:, Results show that pH 12·1 is inimical to benzene biodegradation, and that oxygen concentrations below 0·03 mg l,1 can support aerobic benzene-degrading communities. Significance and Impact of the Study:, These findings will help to guide the treatment of contaminated groundwaters, and raise questions about the extent to which aerobes and anaerobes may interact to effect benzene degradation. [source]

Integration of arbuscular mycorrhiza inoculation in hydroseeding technology: effects on plant growth and inter-species competition

V. Estaún
Abstract Hydroseeding is a technique increasingly used to establish vegetation on large degraded areas, such as large-scale road construction sites and quarries. Native grasses and legume species are used on rehabilitation and restoration projects as a first step in the recovery of such places, prior to the establishment of native forbs and shrubs that occurs at a slower pace. The effect of mycorrhizal inoculation on the development of nine species of grasses and legumes that can be potentially used in restoration processes in the Mediterranean area was studied, in microcosm experiments under greenhouse conditions. The effect of adding arbuscular mycorrhizal (AM) inoculum to a hydroseeding mixture was also investigated in greenhouse and in field conditions. In the hydroseeding experiments the mycorrhizal inoculum was added to the seed slurry in a jet agitated hydroseeding machine and sprayed to the soil surface with a pressurised spray in a one-step application. The study shows that Glomus intraradices Schenk & Smith BEG72 is able to establish the symbiosis when applied at sowing while Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe BEG116 is not. It also confirms that legumes are more highly mycotrophic than grasses. The results of the hydroseeding experiments demonstrate the establishment of the symbiosis using this technology, both in the greenhouse and in the field. Mycorrhizal inoculation improved above ground plant growth and increased the legumes/grasses ratio. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Modulation of primary and secondary infections in epidemics of carrot cavity spot through agronomic management practices

F. Suffert
The relative importance of primary and secondary infections (auto- and alloinfections) in the development of a carrot cavity spot (CCS) epidemic caused by Pythium spp. were investigated. Three cropping factors: fungicide application, soil moisture and planting density, were selected as the key variables affecting the disease tetrahedron. Their effects on: (i) disease measurements at a specific time, (ii) the areas under the disease progress curves (AUDPCs) and (iii) a time-dependent parameter in a pathometric incidence-severity relationship, were studied. Mefenoxam applications 5 and 9 weeks after sowing reduced the intensity of a field CCS epidemic that involved both primary and secondary infections. In microcosm experiments, mefenoxam reduced secondary infections by Pythium violae obtained by transplanting infected carrot roots and slowed disease progress (1·6 lesions per root in treated versus 5·8 lesions in non-treated microcosms). A deficit of soil moisture limited the movement of Pythium propagules to host tissue, and thus reduced primary infections in the field; it also promoted the healing of lesions, limiting lesion expansion and the potential for alloinfections (6·8,7·5 lesions per root in irrigated plots compared with 2·4 lesions in non-irrigated plots). A negative relationship between the mean root-to-root distance and the rate of alloinfections was established in microcosms; a reduction in mean planting density was also effective in limiting CCS development (0·5, 1·6 and 2·0 lesions per root in microcosms containing 8, 16 and 31 roots, respectively). An integrated disease management system based on a combination of cultural methods, such as optimized fungicide application, date of harvest versus soil moisture content, and host density versus planting pattern, may make a useful contribute to the control of CCS. [source]