Microbial alterations of the soil influenced by induced compaction

Compaction is one of the most destructive factors of soil quality, however the effects on the microbial community and enzyme activity have not been investigated in detail so far. The objective of this study was to evaluate the effects of soil compaction caused by the traffic of agricultural machines on the soil microbial community and its enzyme activity. Six compaction levels were induced by tractors with different weights driving over a Eutrustox soil and the final density was measured. Soil samples were collected after corn from the layers 0-0.10 and 0.10-0.20 m. The compaction effect on all studied properties was evident. Total bacteria counts were reduced significantly (by 22-30 %) and by 38-41 % of nitrifying bacteria in the soil with highest bulk density compared to the control. On the other hand, fungi populations increased 55-86 % and denitrifying bacteria 49-53 %. Dehydrogenase activity decreased 20-34 %, urease 44-46 % and phosphatase 26-28 %. The organic matter content and soil pH decreased more in the 0-0.10 than in the 0.10-0.20 m layer and possibly influenced the reduction of the microbial counts, except denitrifying bacteria, and all enzyme activities, except urease. Results indicated that soil compaction influences the community of aerobic microorganisms and their activity. This effect can alter nutrient cycling and reduce crop yields.

Impact of Pseudomonas fluorescens strain CHA0 and a derivative with improved biocontrol activity on the culturable resident bacterial community on cucumber roots

Information on the effects of released wild-type or genetically engineered bacteria on resident bacterial communities is important to assess the potential risks associated with the introduction of these organisms into agroecosystems. The rifampicin-resistant biocontrol strain Pseudomonas fluorescens CHA0-Rif and its derivative CHA0-Rif/pME3424, which has improved biocontrol activity and enhanced production of the antibiotics 2,4-diacetylphloroglucinol (Phl) and pyoluteorin (Plt), were introduced into soil microcosms and the culturable bacterial community developing on cucumber roots was investigated 10 and 52 days later. The introduction of either of the two strains led to a transiently enhanced metabolic activity of the bacterial community on glucose dimers and polymers as measured with BIOLOG GN plates, but natural succession between the two sampling dates changed the metabolic activity of the bacterial community more than did the inoculants. The introduced strains did not significantly affect the abundance of dominant genotypic groups of culturable bacteria discriminated by restriction analysis of amplified 16S rDNA of 2500 individual isolates. About 30-50% of the resident bacteria were very sensitive to Phl and Plt, but neither the wild-type nor CHA0-Rif/pME3424 changed the proportion of sensitive and resistant bacteria in situ. In microcosms with a synthetic bacterial community, both biocontrol strains reduced the population of a strain of Pseudomonas but did not affect the abundance of four other bacterial strains including two highly antibiotic-sensitive isolates. We conclude that detectable perturbations in the metabolic activity of the resident bacterial community caused by the biocontrol strain CHA0-Rif are (i) transient, (ii) similar for the genetically improved derivative CHA0-Rif/pME3424 and (iii) less pronounced than changes in the community structure during plant growth.

Industrial and urban organic wastes increase soil microbial activity and biomass

Microbial processes have been used as indicators of soil quality, due to the high sensitivity to small changes in management to evaluate, e.g., the impact of applying organic residues to the soil. In an experiment in a completely randomized factorial design 6 x 13 + 4, (pot without soil and residue or absolute control) the effect of following organic wastes was evaluated: pulp mill sludge, petrochemical complex sludge, municipal sewage sludge, dairy factory sewage sludge, waste from pulp industry and control (soil without organic waste) after 2, 4, 6, 12, 14, 20, 28, 36, 44, 60, 74, 86, and 98 days of incubation on some soil microbial properties, with four replications. The soil microbial activity was highly sensitive to the carbon/nitrogen ratio of the organic wastes. The amount of mineralized carbon was proportional to the quantity of soil-applied carbon. The average carbon dioxide emanating from the soil with pulp mill sludge, corresponding to soil basal respiration, was 0.141 mg C-CO2 100 g-1 soil h-1. This value is 6.4 times higher than in the control, resulting in a significant increase in the metabolic quotient from 0.005 in the control to 0.025 mg C-CO2 g-1 Cmic h-1 in the soil with pulp mill sludge. The metabolic quotient in the other treatments did not differ from the control (p < 0.01), demonstrating that these organic wastes cause no disturbance in the microbial community.

Reservoir compensation releases : impact on the macroinvertebrate community of the Derwent River, Northumberland, UK-A longitudinal

River regulation for the purposes of public water supply causes the flow regime downstream of a dam to change. Traditionally, in the UK, such regulation was accompanied by requirements for reservoir releases to compensate downstream water users (e.g. industry) for the loss of natural flow (compensation flows). In this article, we compare a unique pre-impoundment macroinvertebrate data set for a regulated upland river with survey data post-impoundment. This allows a longitudinal assessment of the response of the system to regulation. The Derwent River, Northumberland, was impounded in 1966. Impacts on the hydrological regime were quantified by comparing long-term hydrographs, flow duration curves, flow ranges and flashiness indices for the pre-impoundment and post-impoundment periods. The comparison of changes in macroinvertebrate richness and diversity post-impoundment showed that the change in flow regime has had limited effect on the ecological community structure. The flow regime of the Derwent River has become less flashy with fewer extreme events, and the richness and the diversity of macroinvertebrates have, in some cases, increased and at worst have not deteriorated. We suggest that this reflects the strict compensation regime, which has guaranteed minimum flows at all times. Copyright (c) 2012 John Wiley & Sons, Ltd.

Diversity and structure of AMF communities as affected by tillage in a temperate soil.

Arbuscular mycorrhizal fungi (AMF) were studied in differently tilled soils from a long-term field experiment in Switzerland. Diversity and structure of AMF communities were surveyed either directly on spores isolated from the field soil or on spores isolated from trap cultures, planted with different host plants. Single-spore cultures were established from the AMF spores obtained from trap cultures. Identification of the AMF was made by observation of spore morphology and confirmed by sequencing of ITS rDNA. At least 17 recognised AMF species were identified in samples from field and/or trap cultures, belonging to five genera of AMF--Glomus, Gigaspora, Scutellospora, Acaulospora, and Entrophospora. Tillage had a significant influence on the sporulation of some species and non- Glomus AMF tended to be more abundant in the no-tilled soil. The community structure of AMF in the field soil was significantly affected by tillage treatment. However, no significant differences in AMF diversity were detected among different soil tillage treatments. AMF community composition in trap cultures was affected much more by the species of the trap plant than by the original tillage treatment of the field soil. The use of trap cultures for fungal diversity estimation in comparison with direct observation of field samples is discussed.

Community structures of soil animals and survival of land snails on an island of the Ogasawara Archipelago

On Chichijima, one of the Ogasawara (Bonin) Islands located in the Western Pacific Ocean, land snails have declined, the suggested cause being predation pressure by an invasive flatworm (Platydemus manokwari). Soil fauna were investigated in areas where the snail survives, and where it has become extinct. Much of the fauna, dominated by introduced earthworms and ants, was undiminished, however, one undescribed but endemic carabid (Badister sp.), which selectively feeds on land snails, was absent in snail-extinct areas. The invasive flatworm P. manokwari has been reported to feed also on the carcasses of earthworms, as well as on live snails, and is therefore expected to occur in most parts of Chichijima Island. Among other groups, the density of isopods (also dominated by exotic species) was very low, in comparison with the reported ones 30 years ago. Community structure is currently reflected by dominance of earthworms and ants, decline of endemic isopods, and a high frequency of introduced or alien species.

Structure of Poduromorpha (Collembola) communities in "restinga" environments in Brazil

The objectives of this work were to evaluate the richness and diversity of the Poduromorpha fauna in two biotopes in Restinga de Maricá, RJ, Brazil, to identify the characteristic species of each biotope and to determine the relationships between the community structure and the abiotic environmental parameters. Representatives of the Poduromorpha (Collembola) order were studied under an ecological viewpoint in halophyte-psammophyte vegetation and foredune zone in preserved areas of Restinga de Maricá, a sand dune environment in the state of Rio de Janeiro, Brazil. The foredune zone showed the highest diversity, richness and equitability of springtail species. Differences in the fundamental, accessory and accidental species in each environment were encountered. Paraxenylla piloua was found to be an indicator species of the halophyte-psammophyte vegetation, while Friesea reducta, Pseudachorutes difficilis and Xenylla maritima were indicators of the foredune zone. The canonical correspondence analysis indicated pH, organic matter content and soil humidity as the most important factors influencing the spatiotemporal distribution of the species.

Signaling in the Rhizosphere.

Signaling studies in the rhizosphere have focused on close interactions between plants and symbiotic microorganisms. However, this focus is likely to expand to other microorganisms because the rhizomicrobiome is important for plant health and is able to influence the structure of the microbial community. We discuss here the shaping of the rhizomicrobiome and define which aspects can be considered signaling. We divide signaling in the rhizosphere into three categories: (i) between microbes, (ii) from plants to microorganisms, and (iii) from microorganisms to plants. Signals act on diverse organisms including the plant. Mycorrhizal and rhizobial interkingdom signaling has revealed its pivotal role in establishing associations, and the recent discovery of signaling with non-symbiotic microorganisms indicates the important role of communication in shaping the rhizomicrobiome.

The dynamics of biofilm bacterial communities is driven by flow wax and wane in a temporary stream

Biofilm communities are exposed to long periods of desiccation in temporary streams. We investigated how water flow intermittency affected the bacterial community structure colonizing three different streambed compartments in a Mediterranean stream. Massive parallel sequencing revealed different bacterial communities in biofilms from sand sediments and cobbles. Bacterial communities were similar (62% of shared operational taxonomic units) in the epipsammic and hyporheic biofilms, and more diverse than those in the epilithic biofilms. The non-flow phase caused a decrease of bacterial diversity in the biofilms, when communities included only bacterial taxa assumed to be adapted to water stress. The most sensitive bacterial communities to flow intermittency were in the epilithic, where the exposure to physical stress was the highest. In sand sediments a wide group of bacterial taxa was tolerant to desiccation. During non-flow the proliferation of opportunistic taxa in the superficial compartments evidenced the biological link with the terrestrial environment. Bacterial communities better tolerate rewetting than desiccation, since a major number of taxa tolerant to rewetting occurred in all biofilms. Overall, bacterial communities in sandy compartments showed higher resistance to flow intermittency than those in epilithic biofilms

Tree structure and richness in an Atlantic Forest fragment: distance from anthropogenic and natural edges

Approximately 7.2% of the Atlantic rainforest remains in Brazil, with only 16% of this forest remaining in the State of Rio de Janeiro, all of it distributed in fragments. This forest fragmentation can produce biotic and abiotic differences between edges and the fragment interior. In this study, we compared the structure and richness of tree communities in three habitats - an anthropogenic edge (AE), a natural edge (NE) and the fragment interior (FI) - of a fragment of Atlantic forest in the State of Rio de Janeiro, Brazil (22°50'S and 42°28'W). One thousand and seventy-six trees with a diameter at breast height > 4.8 cm, belonging to 132 morphospecies and 39 families, were sampled in a total study area of 0.75 ha. NE had the greatest basal area and the trees in this habitat had the greatest diameter:height allometric coefficient, whereas AE had a lower richness and greater variation in the height of the first tree branch. Tree density, diameter, height and the proportion of standing dead trees did not differ among the habitats. There was marked heterogeneity among replicates within each habitat. These results indicate that the forest interior and the fragment edges (natural or anthropogenic) do not differ markedly considering the studied parameters. Other factors, such as the age from the edge, type of matrix and proximity of gaps, may play a more important role in plant community structure than the proximity from edges.

Diameter and height distributions in a gallery forest tree community and some of its main species in central Brazil over a six-year period (1985-1991)

(Diameter and height distributions in a gallery forest tree community and some of its main species in central Brazil over a six-year period (1985-1991)). The diameter and height structure were studied over six years in approximately 64 ha of the Gama gallery forest in Brasília, DF. Trees from 10 cm dbh were measured every three years from 1985 in 151 (10 x 20 m) permanent plots. Natural regeneration (individuals under 10 cm dbh) was measured in subplots within the 200 m² plots. Most individuals and species were under 45 cm diameter and 20 m high while the maximum diameter for individual species ranged from 30 to 95 cm. The diameter structure was typical of a mixed tropical forest with the number of individuals decreasing with increasing size classes and showing little change over the six years. The most abundant species occupy different positions in the canopy and have different size structures.

Variations inter journalières dans la structure des communautés de poissons : implications pour le développement de modèles de qualité d'habitats

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Diversité et structure du zooplancton : importance pour la conservation de la biodiversité aquatique en zone urbaine

L'écologie urbaine est un nouveau champ de recherche qui cherche à comprendre les structures et les patrons des communautés et des écosystèmes situés dans des paysages urbains. Les petits plans d’eau sont connus comme des écosystèmes aquatiques qui peuvent contenir une biodiversité considérable pour plusieurs groupes taxonomiques (oiseaux, amphibiens, macroinvertébrés), ce qui en fait des écosystèmes intéressants pour les études de conservation. Cependant, la biodiversité du zooplancton, un élément central des réseaux trophiques aquatiques, n’est pas entièrement connue pour les plans d’eaux urbains et devrait être mieux décrite et comprise. Cette étude a évalué les patrons de biodiversité des communautés zooplanctoniques dans des plans d’eau urbains sur l’Ile de Montréal et leurs sources de variation. Des suggestions pour l’évaluation et la conservation de la biodiversité sont aussi discutées. La biodiversité zooplanctonique des plans d’eaux urbains s’est avérée être assez élevée, avec les cladocères et les rotifères montrant les contributions à la diversité gamma et bêta les plus élevées. Sur l’ensemble des plans d’eau, il y avait une corrélation négative entre les contributions à la bêta diversité des cladocères et des rotifères. Au niveau de chaque plan d'eau, la zone littorale colonisée par des macrophytes s'est avérée être un habitat important pour la biodiversité zooplactonique, contribuant considérablement à la richesse en taxons, souvent avec une différente composition en espèces. Les communautés zooplanctoniques répondaient aux facteurs ascendants et descendants, mais aussi aux pratiques d’entretien, car le fait de vider les plans d’eau en hiver affecte la composition des communautés zooplanctoniques. Les communautés de cladocères dans ces plans d’eau possédaient des quantités variables de diversité phylogénétique, ce qui permet de les classer afin de prioriser les sites à préserver par rapport à la diversité phylogénétique. Le choix des sites à préserver afin de maximiser la diversité phylogénétique devrait être correctement établi, afin d’eviter de faire des choix sous-optimaux. Cependant, pour des taxons tels que les cladocères, pour lesquels les relations phylogénétiques demeurent difficiles à établir, placer une confiance absolue dans un seul arbre est une procédure dangereuse. L’incorporation de l’incertitude phylogénétique a démontré que, lorsqu’elle est prise en compte, plusieurs différences potentielles entre la diversité phylogenétique ne sont plus supportées. Les patrons de composition des communautés différaient entre les plans d’eau, les mois et les zones d’échantillonnage. Etant donné les intéractions sont significatives entres ces facters; ceci indique que tous ces facteurs devraient êtres considérés. L’urbanisation ne semblait pas sélectionner pour un type unique de composition des groupes alimentaires, étant donné que les communautés pouvaient changer entres des assemblages de types alimentaires différents. Les variables environnementales, surtout la couverture du plan d’eau en macrophytes, étaient des facteurs importants pour la biodiversité zooplanctonique, affectant la richesse spécifique de divers groupes taxonomiques et alimentaires. Ces variables affectaient aussi la composition des communautés, mais dans une moindre mesure, étant des variables explicatives modestes, ce qui indiquerait le besoin de considérer d’autres processus.

Depth wise variation of microbial load in the soils of midland region of Kerala: a function of important soil physicochemical characteristics and nutrients

Soil microorganisms play a main part in organic matter decomposition and are consequently necessary to soil ecosystem processes maintaining primary productivity of plants. In light of current concerns about the impact of cultivation and climate change on biodiversity and ecosystem performance, it is vital to expand a complete understanding of the microbial community ecology in our soils. In the present study we measured the depth wise profile of microbial load in relation with important soil physicochemical characteristics (soil temperature, soil pH, moisture content, organic carbon and available NPK) of the soil samples collected from Mahatma Gandhi University Campus, Kottayam (midland region of Kerala). Soil cores (30 cm deep) were taken and the cores were separated into three 10-cm depths to examine depth wise distribution. In the present study, bacterial load ranged from 141×105 to 271×105 CFU/g (10cm depth), from 80×105 to 131×105 CFU/g (20cm depth) and from 260×104 to 47×105 CFU/g (30cm depth). Fungal load varies from 124×103 to 27×104 CFU/g, from 61×103 to110×103 CFU/g and from 16×103 to 49×103 CFU/g at 10, 20 and 30 cm respectively. Actinomycetes count ranged from 129×103 to 60×104 CFU/g (10cm), from 70×103 to 31×104 CFU/g (20cm) and from 14×103 to 66×103 CFU/g (30cm). The study revealed that there was a significant difference in the depthwise distribution of microbial load and soil physico-chemical properties. Bacterial, fungal and actinomycetes load showed a decreasing trend with increasing depth at all the sites. Except pH all other physicochemical properties showed decreasing trend with increasing depth. The vertical profile of total microbial load was well matched with the depthwise profiles of soil nutrients and organic carbon that is microbial load was highest at the soil surface where organics and nutrients were highest

Ecology And Seasonal Variation Of Microalgal Community In An Oil Refinery Effluent Holding Pond: Monitoring And Assessment

The microalgal community as primary producers has to play a significant role in the biotic and abitoic interactions of any aquatic ecosystem. Whenever a community is exposed to a pollutant, responses can occur because individuals acclimate to pollutant caused changes and selection can occur favouring resistant genotypes within a population and selection among species can result in changes in community structure. The microalgal community of industrial effluent treatment systems are continuously exposed to pollutants and there is little data available on the structure and seasonal variation of microalgal community of industrial effluent holding ponds, especially of a complex effluent like that of refinery. The aim of the present study was to investigate the annual variation in the ecology, biomass, productivity and community structure of the algal community of a refinery effluent holding pond. The results of the study showed the pond to be a eutrophic system with a resistant microalgal community with distinct seasonal variation in species composition