Total Microbial Activity Research Articles

Different vegetable crop rotations affect soil microbial communities and soilborne diseases of potato and onion: literature review and a long-term field evaluation

A major concern in potato and onion production worldwide is the sustainability of crop production systems using short-term rotations. Although rotation crops are known to influence soil microbial communities, few long-term field studies have investigated effects of potato and onion crop rotations on soil microflora and soilborne diseases. A long-term trial (10 years) was established in New Zealand in the 2004–05 season to determine changes in soil characteristics, soil biological communities, plant productivity and soilborne diseases resulting from different crop rotations. Six different crop rotation ‘treatments’ were used: three were onion-focused and three were potato-focused. For both the onion- and potato-focused rotations, one treatment was continual monoculture, one was biennial alternating onion and potato (‘conventional’ rotation, common local commercial practice) and one was a 4-year cycle where the onion or potato crops were grown every fourth season with different crops in the intervening seasons (‘sustainable’ rotation). The results of the rotations were evaluated at the end of 2012–13, nine growing seasons after the trial began. Soils from the three potato-focused rotations had similar microbial biomass carbon (C) and nitrogen (N), total C and N, and enzyme activity, but had different microbial activity parameters. Soils from the three onion rotations differed in organic matter content, total C and N, enzyme activity and carbohydrate utilization. The main factor correlated with potato diseases (stem canker, black scurf) and crop yields was the amount of Rhizoctonia inoculum in the soil. Onion yields in 2012–13 were correlated with the severity of pink root during the growing season. Total microbial activity in soil gave better relationships to soilborne disease incidence (Rhizoctonia stem canker of potato or pink root of onion) and to crop yields, than soil chemical parameters (pH, nutrient status, C:N ratio) or other microbiological parameters (microbial biomass, total culturable bacteria and fungi, and microbial diversity). This research has broadened understanding of effects of crop rotations on soil microbial community characteristics, soilborne diseases and crop productivity of potatoes and onions grown in a soil and an area where intensive vegetable production is common. This knowledge will assist growers to increase crop yields and reduce soilborne pathogens in a sustainable manner. Based on the results from this study, intensive potato and onion production should require these crops to be grown within 4-year crop rotations in order to foster sustainable yields and minimize soilborne diseases.

Effects of enhanced UV-B radiation on the diversity and activity of soil microorganism of alpine meadow ecosystem in Qinghai-Tibet Plateau.

The effects of enhanced UV-B radiation on abundance, community composition and the total microbial activity of soil bacteria in alpine meadow ecosystem of Qinghai-Tibet Plateau were investigated. Traditional counting and 16S rRNA gene sequencing were used to investigate the culturable bacteria and their composition in soil, meanwhile the total microbial activity was measured by microcalorimetry. The population of soil culturable bacteria was slightly reduced with the enhanced UV-B radiation in both of the two depths, 2.46 × 10(6) CFU/g in upper layer (0-10 cm), 1.44 × 10(6) CFU/g in under layer (10-20 cm), comparing with the control (2.94 × 10(6) CFU/g in upper layer, 1.65 × 10(6) CFU/g in under layer), although the difference was not statistically significant (P > 0.05). However, the bacteria diversity decreased obviously due to enhanced UV-B, the number of species for upper layer was decreased from 20 to 13, and from 16 to 13 for the lower layer. The distribution of species was also quite different between the two layers. Another obvious decrease induced by enhanced UV-B radiation was in the total soil microbial activities, which was represented by the microbial growth rate constant (k) in this study. The results indicated that the culturable bacteria community composition and the total activity of soil microbes have been considerably changed by the enhanced UV-B radiation.

Temperature Sensitivity and Soil Organic Carbon Pools Decomposition under Different Moisture Regimes: Effect on Total Microbial and Enzymatic Activity

The soils of the world store significantly more carbon than present in the atmosphere. However, there is still no consensus regarding the effects of climate change, i.e. increase in temperature on global soil carbon stocks. An incubation experiment was conducted under a temperature range (5–45°C) and moisture conditions, i.e. U1–U5 (20–100% water‐holding capacity) with the objective to investigate temperature sensitivity of labile and recalcitrant organic carbon pools, total microbial activity, and soil extracellular enzymes, i.e. phenol oxidase and catalase activity in an Ultisol soil. The maximum increase in the labile organic carbon pool, i.e. water soluble organic carbon (3.52‐fold), microbial biomass carbon (2.31‐fold), readily mineralizable carbon (6.16‐fold), permanganate oxidized organic carbon (2.81‐fold), and reducing sugar carbon (3.97‐fold) was observed at 35°C, whereas the effect at other temperatures was in the order 25 > 45 > 15 > 5°C. The total organic carbon (TOC) tended to decrease with the increased temperature (from 5–35°C), therefore, maximum TOC (14.7 g kg−1) was observed at 5°C, and minimum (1.76 g kg−1) at 45°C. Conversely, the highest increase (6.48‐fold) in the recalcitrant organic carbon pool was noticed at 45°C, and the impact of other temperatures was in the order 35 > 25 > 15 > 5°C. The maximum increase in the total microbial activity (13.68‐fold) and soil enzymes, phenol oxidase and catalase (3.94 and 3.98‐fold, respectively) activity was observed at 35°C, while the influence of other temperature ranges was in the order 25 > 45 > 15 > 5°C. The effect of moisture regimes on the temperature sensitivity of organic carbon pools, total microbial and enzymatic activity was in the order U3 > U4 > U2 > U1 > U5.

Metabolic profiles of microorganisms associated with the halophyte Salicornia europaea in soils with different levels of salinity

Plants have evolved a wide range of adaptation mechanisms that enable them to grow and develop in environments of high soil salinity. We examine the plant—microbial interactions of Salicornia europaea (Herbaceae) as potential mechanisms responsible for the high tolerance of halophytes to saline conditions. We evaluated the impact of different NaCl concentrations on microorganisms associated with S. europaea growing at 2 saline sites in central Poland: a salty meadow in the vicinity of a soda factory (anthropogenic salinity) and an area affected by natural brine (landscape park). The community-level physiological profiles of microorganisms associated with the plant were determined for endophytes from the roots, rhizosphere, and salt-affected soil. The highest total microbial metabolic activity, irrespective of the test site, was always in the rhizosphere, while the activity of endophytic and soil populations depended on salinity. In general, a higher total metabolic activity was observed at the test site exhibiting higher salt concentration. We propose that increased metabolic activity of microbial populations under increased salt stress can significantly contribute to the site adaptation of halophytes to saline conditions.

Effect of fly ash application on soil microbial response and heavy metal accumulation in soil and rice plant

Fly ash (FA), a byproduct of coal combustion in thermal power plants, has been considered as a problematic solid waste and its safe disposal is a cause of concern. Several studies proposed that FA can be used as a soil additive; however its effect on microbial response, soil enzymatic activities and heavy metal accumulation in soil and grain of rice (cv. Naveen) to fly ash (FA) application was studied in a pot experiment during dry season 2011 in an Inceptisol. Fly ash was applied at a rate of zero per cent (FS), five per cent (FA5), ten per cent (FA10), twenty per cent (FA20), 40 per cent (FA40) and 100 per cent (FA100) on soil volume basis with nitrogen (N), phosphorus (P) and potassium (K) (40:20:20mg N:P:Kkg−1 soil) with six replications. Heavy metals contents in soil and plant parts were analysed after harvest of crop. On the other hand, microbial population and soil enzymatic activities were analysed at panicle initiation stage (PI, 65 days after transplanting) of rice. There was no significant change in the concentration of zinc (Zn), iron (Fe), copper (Cu), manganese (Mn), cadmium (Cd) and chromium (Cr) with application of fly ash up to FA10. However, at FA100 there was significant increase of all metals concentration in soil than other treatments. Microorganisms differed in their response to the rate of FA application. Population of both fungi and actinomycetes decreased with the application of fly ash, while aerobic heterotrophic bacterial population did not change significantly up to FA40. On the other hand, total microbial activity measured in terms of Fluorescein diacetate (FDA) assay, and denitrifiers showed an increased trend up to FA40. However, activities of both alkaline and acid phosphatase were decreased with the application of FA. Application of FA at lower levels (ten to twenty per cent on soil volume basis) in soil enhanced micronutrients content, microbial activities and crop yield.

Metabolic potential of microorganisms associated with the halophyte Aster tripolium L. in saline soils

Increased soil salinization may be caused by a natural (e.g. climate change) and anthropogenic (e.g. improper fertilization and irrigation of agricultural land) factors. The submitted work assumes that microorganisms associated with plant halophytes have a unique metabolic properties that can stimulate plant growth under salt stress. The aim of the study was to determine the abundance and metabolic biodiversity of endophytic and rhizosphere microorganisms co-existing with Aster tripolium L. and compare them with the properties of soil microorganisms not affected by plant roots at a salty meadows in the vicinity of a soda factory (central Poland). In order to select halotolerant and halophilic microorganisms culture medium was enriched with various concentrations of NaCl (0, 100, 200, 400, 600 mM NaCl). Total metabolic activity of endophytic, rhizosphere and soil populations was measured to compare the community-level physiological profiles. Results of our study revealed that bacterial and fungal density increased in the following order: endophytes < soil < rhizosphere. Only the highest concentration (600 mM) of NaCl decreased the number of microorganisms. The highest total microbial metabolic activity was observed for the rhizosphere, while the activity of endophytes was higher compare to soil populations. To carbon sources which significantly differentiated zones belonged: D-lactose, 4-hydroxybenzoic acid and L-asparagine. The results are preliminary studies leading to the development of inoculum based on selected microbial halotolerant and halophilic strains which can be used in agriculture and/or recultivation of saline soils.

English

Geophysical investigation was carried out to detect the spread of sewage effluent and to locate the sources and delineate migration paths and the extent of leachate plume. The study was to find out the geological formations that are the most conductive layers in the sewage site for the free flow of the contaminants. Soil tests showed that hydraulic conductivity, bulk density and water retention were variable in sewage soil, but consistent in soil unaffected by sewage. In sewage soil, maize crops performance, organic matter, total nitrogen exchangeability,  cations  exchange capacity and sodium were significantly enhanced than in non-sewage soil. In sewage soil, electrical conductivity (EC), zinc (Zn), lead (Pb), copper (Cu), Cadmium (Cd), salt concentration and other saline properties, total faecal coliform and microbial activities were high. Twelve vertical electrical soundings (VES) points with Omega Terrameter were used in the Schlumberger Array configuration which the geoelectrical section from the resistivity data revealed seven subsurface layers. Three low resistivity zones were detected as correspondent zones to the plumes. The comparative evaluation of the 3-D stack model of the resistivity of layers with respect to depth suggested that these three low resistivity layers were contaminated, especially as the depth to water table is more than 100m. The flow direction of the contaminant plume is northwest to southwest as indicated by stack model of the low resistivity layers. Generally, the contaminant plume is a threat to ecosystem and a great health problem to people living around the sewage site.   Key words:   Delineate, contamination, leachate, sewage effluent, saline, ecosystem.

English

Geophysical investigation was carried out to detect the spread of sewage effluent and to locate the sources and delineate migration paths and the extent of leachate plume. The study was to find out the geological formations that are the most conductive layers in the sewage site for the free flow of the contaminants. Soil tests showed that hydraulic conductivity, bulk density and water retention were variable in sewage soil, but consistent in soil unaffected by sewage. In sewage soil, maize crops performance, organic matter, total nitrogen exchangeability,  cations  exchange capacity and sodium were significantly enhanced than in non-sewage soil. In sewage soil, electrical conductivity (EC), zinc (Zn), lead (Pb), copper (Cu), Cadmium (Cd), salt concentration and other saline properties, total faecal coliform and microbial activities were high. Twelve vertical electrical soundings (VES) points with Omega Terrameter were used in the Schlumberger Array configuration which the geoelectrical section from the resistivity data revealed seven subsurface layers. Three low resistivity zones were detected as correspondent zones to the plumes. The comparative evaluation of the 3-D stack model of the resistivity of layers with respect to depth suggested that these three low resistivity layers were contaminated, especially as the depth to water table is more than 100m. The flow direction of the contaminant plume is northwest to southwest as indicated by stack model of the low resistivity layers. Generally, the contaminant plume is a threat to ecosystem and a great health problem to people living around the sewage site.   Key words:   Delineate, contamination, leachate, sewage effluent, saline, ecosystem.

Fluorescent components of organic matter in wastewater: Efficacy and selectivity of the water treatment

Characterization of organic matter (OM) present in treated wastewater (TWW) after various treatment stages is important for optimizing wastewater recycling. The general aim of this research was to carry out a long-term examination of OM in wastewater along the treatment, by applying excitation-emission matrices (EEM) fluorescence spectroscopy and parallel factor analysis (PARAFAC). Fluorescent OM was examined in water samples obtained from four wastewater treatment plants (WWTPs) in Israel for 20 months. The PARAFAC analysis of EEMs of water samples from the four WWTPs yielded six components. The fluorescent components included proteinaceous tryptophan-like matter (C1), three humic-like components (C2–C4), a component (C5) that was characterized by excitation and emission with a distinct vibrational structure similar to that of pyrene and a component (C6) that was characterized by the excitation and emission spectra demonstrating two peaks where the appearance of two emission peaks was suggested to reflect the formation of an intra-molecular exyplex. The biological treatment strongly reduced the concentration of component C1 thus increasing the overall fraction of humic-like OM over the proteinaceous OM in the treated water. The fluorescence of component C1 could therefore be used as an indicator of the biological treatment efficacy. The concentration of the humic-like component C2 characterized by excitation and emission maxima at <240,305/422 nm, respectively, was also sensitive to biological treatment. The soil aquifer treatment was not effective in completely eliminating the fingerprints of the initial wastewater. The concentrations of the fluorescent components in wastewater after the biological treatment were only slightly affected by filtration (0.45 μm) of the samples. For water sampled prior to the biological treatment, the 0.45 μm filtration had the most pronounced effect on concentrations of the proteinaceous matter and component C6. Strong positive correlations were found between concentrations of component C1 and total carbon (TC) in wastewater samples from the WWTPs thus suggesting the proteinaceous fluorescence in wastewater as an indicator for TC reduction. Chemical oxygen demand (COD) and the fluorescein diacetate hydrolyzing activity (a measure for the total microbial activity) were strongly positively correlated with the concentrations of components C1–C3 thus suggesting the fluorescence of these components as indicators for reduction in COD and the total microbial activity in wastewater.

Effect of butachlor (G) on soil enzyme activity

Soil enzymes play a crucial role in maintaining soil functions. Pesticide application to crop plants can potentially interfere with soil enzyme activity. We evaluated the impact of butachlor (G), a widely used herbicide, on total soil microbial activity and activity of various soil enzymes, including alkaline phosphatase, protease, urease and amidase at different application rates under flooded and un-flooded conditions in a laboratory experiment. The pesticide treatment had an inhibitory effect on dehydrogenase activity under un-flooded conditions and stimulatory effect under flooded conditions. Phosphatase activity was stimulated under most of the applied concentrations both under flooded as well as un-flooded conditions. Protease activity was initially stimulated but decreased towards the end of the experiment under un-flooded conditions. Under flooded conditions the effect of butachlor on the activity of protease was stimulatory. Urease activity was reduced by pesticide treatment under un-flooded conditions, but response was inconsistent under flooded conditions. Amidase activity showed a fluctuating behaviour. Thus, the results allowed us to conclude that the use of butachlor alters soil enzyme activity, and its potential implications could be examined by future studies.

A feasibility study on the bioremediation of hydrocarbon-contaminated soil from an Alpine former military site: Effects of temperature and biostimulation

A laboratory feasibility study on the bioremediation of hydrocarbon-contaminated soil from an Alpine former military site was conducted over a period of 30weeks. We determined the effects of temperature (10°C and 20°C) and of various biostimulation treatments (inorganic nitrogen–phosphorus–potassium fertilization and the two commercial products Inipol EAP22 and Terramend) versus natural attenuation on the loss of total petroleum hydrocarbons (TPH), microbial activity (soil respiration) and community composition (phospholipid fatty acids, PLFA). The hydrocarbon contamination was removed almost completely (up to 92.7%) at 20°C, while at 10°C losses up to 69% were obtained. Biostimulation by the addition of nutrients had a significantly stimulating effect on the biodegradation activity of the indigenous soil microorganisms; however, a considerable amount of hydrocarbon loss could be attributed to natural attenuation. Shifts in microbial community composition during bioremediation included the significant increase of soil fungi at 10°C and of Gram-negative soil bacteria at 20°C. Significantly positive correlations between hydrocarbon loss, soil respiration and patterns of phospholipid fatty acids demonstrated the involvement of a wide range of soil microorganisms (Gram-positive and Gram-negative bacteria, fungi) in the bioremediation of the investigated soil.

The influence of earthworms on nutrient dynamics during the process of vermicomposting

In the present study the potential of the earthworm Eisenia andrei to modify chemical and microbiological properties, with a special focus on the nutrient content of fresh organic matter, was evaluated during 16 weeks of vermicomposting of cattle manure and sewage sludge. Samples were periodically collected in order to determine the changes in inorganic nitrogen (N), in total microbial biomass and activity, as well as in the total and available content of macro- and micronutrients. An optimal moisture level, ranging from 75% to 88%, was maintained throughout the process. The content of organic matter decreased over time, but no changes were found in this parameter as a result of earthworm activity. The carbon/N ratio rapidly decreased, but only in the manure, reflecting rapid decomposition and mineralisation of the organic matter by the earthworms. An increase in N mineralisation was also attributable to the presence of earthworms, although in the manure this effect was hardly detectable before the eighth week of vermicomposting. Earthworm activity also enhanced the total content of potassium, calcium and iron together with an increase in the availability of phosphorus and zinc. We did not detect a significant earthworm effect on microbial respiration, but their activity increased greatly microbial biomass nitrogen in sewage sludge.

Effects of alumina trihydrate (ATH) on formation of biofilms settled on inert carriers of polyethylene terephthalate (PET)

Alumina trihydrate (ATH), one of typical complexes of aluminum (Al), was selected to study its effects on the formation of biofilms settled on inert carriers made of polyethylene terephthalate (PET) filaments. Four identical biological reactors were developed to cultivate biofilms under a series of ATH concentrations. Three-dimensional elastic inert PET carriers were used as the biofilm substrata. The biofilm characteristics including the amounts of total biofilm, extracellular polymeric substances (EPS) productions, active biomass, and microbial activity, were investigated. The impact of Al toxicity on the formation of biofilms was also discussed. The results showed that the colloidal ATH was easily adhered to the inert carriers, and the effects of ATH on the formation of biofilms colonized on the inert carriers were clearly observed. Compared to the biofilm characteristics when ATH was absent, the presence of ATH could increase the amounts of total biofilm production, EPS production, active biomass, and microbial activity: when the ATH concentrations reached 0.1, 0.2, and 0.5 mg/L (as Al3+), the total biofilm amount would increase to 1.44, 2.14, and 2.60 times, respectively, and the EPS production would enhance to 1.21, 1.60, and 1.85 times, respectively. Similar ratios for EPS production were also obtained for the corresponding active biomass and microbial activity. These results suggested that ATH is beneficial to the formation of biofilms settled on inert carriers, and the impact of Al toxicity seems to be insignificant in this study on the colonized microbes and the biofilm formation, probably due to the low ATH concentration (0.5 mg/L as Al3+ in maximum) in the reactors.

Increased microbial activity and nitrogen mineralization coupled to changes in microbial community structure in the rhizosphere of Bt corn

The interactions between plant roots and soil microorganisms are essential for the function and stability of ecosystems, primary agricultural production and plant health. Despite the importance of soil microbes the response of these microbes to large-scale cultivation of genetically modified (GM) crops is still poorly understood. This study evaluated the potential impact of two lines of transgenic Bt maize on rhizosphere microorganisms. A time-course field experiment was conducted over a period of two years in two fields in Guadalajara (Spain) with monthly sampling from April to September. Rhizosphere soil was collected from transgenic (TG) and unmodified (WT) maize plants from each field and sampling time for the analysis of several important functional and structural soil quality parameters. Total microbial activity, as determined by H3-Thymidine and C14-Leucine incorporation, was found to be higher in the rhizospheres of the transgenic plants. Similarly, differences in potential ammonification and nitrification were observed in the second year of the study. In contrast, bacterial and fungal microbial catabolic abilities, as determined by Biolog ECO and FF plate analyses, respectively, were more influenced by sampling time than the transgenic nature of the plants. Microbial community structure was also studied by bacterial and phylum-specific PCR-DGGE and PCR cloning approaches. In general, differences were again more pronounced between sampling times, as opposed to between TG versus WT plants, although marked differences were observed within the Betaproteobacteria between plant lines. For the first time it describes the presence of Iamiaceae family in soil, specifically to TG plant rhizosphere. To summarize, the study showed that some important properties of rhizopshere microbes may be impacted by Bt maize cultivation and highlighted the fact that such potential effects need to be viewed within the context of seasonal and spatial variability.

Short-term impact of olive mill wastewater (OMWW) applications on the physico-chemical and microbiological soil properties of an olive grove in Argentina

The purpose of this work was to investigate the effects of spreading olive oil mill wastewater (OMWW) on soil biochemical parameters and olive production in an organically managed olive orchard. The experiment was carried out with three different doses of OMWW (80, 160 and 500 m3 ha−1) and a control (untreated soil). Three samplings were done at 10, 30 and 90 days after the administration of the byproduct. OMWW application differentially modified the biochemical properties of the soil analyzed. Organic matter, organic carbon, total nitrogen and extractable phosphorus soil contents increased proportionally with each increasing dose. The values of these parameters decreased gradually with time. Total microbial activity was altered and the OMWW 500 m3 ha−1 treatment proved to be the most active when compared with the other applied doses. OMWW agricultural application also modified the structure of soil microbial communities, particularly affecting Gram positive and negative bacteria, while fungal biomass did not show consistent changes. Although there was a salinity increase in the treated soil, especially at the highest dose, the productive parameters analyzed (fruit and oil tree−1) were not affected. In light of the obtained results, we consider that low dose of OMWW could be considered an alternative farming practice for semiarid regions.

Litterfall interception by understorey vegetation delayed litter decomposition in Cinnamomum camphora plantation forest

This study was carried out to improve our understanding of the interception effect of understorey vegetation on litter decomposition in Cinnamomum camphora plantation forest of subtropical China. The interception simulation experiment in field was performed to determine how the litterfall interception delayed the leaf litter decomposition of C. camphora, by comparing the difference in variables among 4 litter interception locations. The results showed that total mass loss, lignin loss, cellulose loss, microbial activities (CO2 release, fungal biomass and enzyme activities), and water content except nitrogen for litters on the crown were significantly lower than that of litters without interception. The maximum mass loss difference value among litter locations reached 35 %, indicative of obvious decomposition delay by the understorey. Litter CO2 release, enzyme activities and water content exhibited a clear seasonal pattern, suggesting a strong relation between the degree of microbial activities and the succession of cold and warm as well as moist and dry periods. A clear nitrogen increase was observed in this experiment, indicating persistent immobilization. No clear variation pattern in nitrogen content was observed in this study, which was probably mixed by the N precipitation from acid rain. The litterfall interception delayed the decomposition of leaf litter, displaying slow decomposition rate and inhibitive microbial activities by interception, which presumably resulted from low water content on the crown.

Sampling Design Optimization on Arable Lands for Integrated Soil Monitoring for Sustainable Production

Proper experimental design that ensures effective sampling of each recorded environmental variable is essential during planning integrated soil-monitoring programs with the aim of assessing the ecological state of soils. In our study, three different regular sampling designs (standard, 50,000 m2; reduced area, 635 m2; and reduced area and sampling size, 2500 m2) were tested, and the required sampling sizes for 10%, 20%, and 40% minimum detectable change were calculated. Sampling designs were tested from the aspect of the most effective sampling, a sampling with the greatest precision and the least bias. The parameters determined in this study were the following: total microbial activity, concentration of 14 potentially toxic microelements, and basic soil physical and chemical characteristics. The results are presented by the example of total microbial activity and microelement concentration studies. Twenty to 120 soil samples were taken from each selected arable land under intensive and organic cultivation as well as from a pasture and protected grassland, considered as a control. It was concluded that both for microbial activity and microelement concentration measurements of 10% minimum detectable change requires enormous sampling effort at each site and sampling design. The required sampling size is especially high at the organic sites and the grassland, because the high standard deviation, and especially high mean total microbial activity. With a sampling using either the standard or reduced area design, 20% difference in total microbial activity can be detected using a reasonable (<25) sampling size. However, reduced area design minimizes spatial heterogeneity, thus requires smaller sampling effort, and can be an ideal compromise. In the case of microelement concentration, standard sampling design was more sufficient to detect a 20% change. Designs that proved to be most efficient in this study have been combined into a joint sampling design that will be applied in the first cycle of the new Hungarian Soil Degradation Monitoring System.

Metabolic potential of microorganisms associated with the halophyte Aster tripolium L. in saline soils

Increased soil salinization may be caused by a natural (e.g. climate change) and anthropogenic (e.g. improper fertilization and irrigation of agricultural land) factors. The submitted work assumes that microorganisms associated with plant halophytes have a unique metabolic properties that can stimulate plant growth under salt stress. The aim of the study was to determine the abundance and metabolic biodiversity of endophytic and rhizosphere microorganisms co-existing with Aster tripolium L. and compare them with the properties of soil microorganisms not affected by plant roots at a salty meadows in the vicinity of a soda factory (central Poland). In order to select halotolerant and halophilic microorganisms culture medium was enriched with various concentrations of NaCl (0, 100, 200, 400, 600 mM NaCl). Total metabolic activity of endophytic, rhizosphere and soil populations was measured to compare the community-level physiological profiles. Results of our study revealed that bacterial and fungal density increased in the following order: endophytes < soil < rhizosphere. Only the highest concentration (600 mM) of NaCl decreased the number of microorganisms. The highest total microbial metabolic activity was observed for the rhizosphere, while the activity of endophytes was higher compare to soil populations. To carbon sources which significantly differentiated zones belonged: D-lactose, 4-hydroxybenzoic acid and L-asparagine. The results are preliminary studies leading to the development of inoculum based on selected microbial halotolerant and halophilic strains which can be used in agriculture and/or recultivation of saline soils.

Plant growth-promoting rhizobacteria suppressive to Phytophthora blight affect microbial activities and communities in the rhizosphere of pepper (Capsicum annuum L.) in the field

Two plant growth-promoting rhizobacteria, Pseudomonas corrugata CCR80 and Chryseobacterium indologenes ISE14, previously reported as suppressive to Phytophthora blight of pepper caused by Phytophthora capsici in the field were selected for use of this study. The effects of the strains on microbial activities, populations, and communities in pepper rhizosphere with or without pathogen inoculation were examined at 40, 80, and 120 days after transplanting (DAT) in the field in 2008 and 2009. To investigate the microbial effects, we used culture-dependent and -independent techniques such as plate counts on selective media, and fluorescein diacetate and denaturing gradient gel electrophoresis (DGGE) analyses. Root treatment with the strains increased total microbial activities in rhizosphere soil compared with controls (untreated, metalaxyl, or Escherichia coli DH5α) over the sampling time regardless of pathogen inoculation; however, microbial activities were greatly decreased in all treatments at 40–80DAT. The strains also impacted the populations of bacterial and fungal functional groups. Eight fungal species, frequently observed on the medium for total fungi, were identified; these populations were significantly affected by the treatments: three species by metalaxyl, one by strain DH5α, one by strain ISE14, and none by strain CCR80 in both years. The DGGE analysis revealed that the strains affected bacterial and fungal community structure; the test strains increased the bacterial community composition, especially at 80DAT, but had little effect on fungal community at later DAT. Taken together, strains CCR80 and ISE14 increased microbial activities and community composition, and affected certain microbial populations in the rhizosphere of pepper plants in the field, which might play significant roles in the suppression of Phytophthora blight of pepper.

Biodegradation of Crude Oil in Contaminated Soils by Free and Immobilized Microorganisms

The efficiencies of free and immobilized bacterial cultures of petroleum hydrocarbon degraders were evaluated and compared in this study. Hydrocarbon-degrading microbial communities with high tolerance to and high degrading ability of crude oil were obtained from the soil contaminated with crude oil in the Yellow River Delta. Then, the microbial cells were immobilized in sodium alginate (SA) beads and sodium alginate-diatomite (SAD) beads. The biodegradation of crude oil in soil by immobilized cells was compared with that by free cells at three inoculation concentrations, 1 × 104 colony forming units (cfu) kg−1 (low concentration, L), 5 × 104 cfu kg−1 (medium concentration, M), and 1 × 105 cfu kg−1 (high concentration, H). At 20 d after inoculation, the maximum degradation rate in the immobilized systems reached 29.8% (SAD-M), significantly higher (P < 0.05) than that of the free cells (21.1%), and the SAD beads showed greater degradation than the SA beads. Moreover, both microbial populations and total microbial activity reached significantly higher level (P < 0.05) in the immobilized systems than free cell systems at a same initial inoculation amount. The scanning electronic microscope (SEM) images also confirmed the advantages of the immobilized microstructure of SAD beads. The enhanced degradation and bacterial growth in the SAD beads indicated the high potential of SAD beads as an effective option for bioremediation of crude oil-contaminated soils in the Yellow River Delta.