Length Of Hyphae Research Articles

Immunological Features of Macrophages Induced by Various Morphological Structures of Candida albicans

Candida albicans is a dimorphic fungus that commensally colonizes human mucosal surfaces. The aim of this study was to assess the role of different C. albicans morphologies in inducing pattern recognition receptors (PRRs) and cytokines in macrophages. Macrophages may respond to pathogen-associated molecular patterns via TLR2 and TLR4 by expressing cytokines. The hyphal transition of C. albicans was induced by 20% serum (S), RPMI-1640 (R), or 39℃ culture (H). Macrophages were then challenged with either yeast (Y) or different hyphae cultures of C. albicans, followed by RT-PCR and FACS analysis of PRRs expression. In addition, macrophages were stimulated with either yeast or different hyphae cultures of C. albicans used by RT-PCR and Bio-Plex analysis of cytokines production. Macrophages expressed high levels of TLR4 and dectin-1 after stimulation with Y cells. In contrast, stimulation with H or R cells strongly increased the expression of TLR2 and dectin-2. Stimulation with Y cells significantly enhanced the expression of IL-1β and weakly increased the expression of IL-6 and IL-12. Stimulation with hyphal cells (S, R, and H) strongly increased IL-10 expression, but weakly reduced IL-1β expression. The phagocytosis activity and NO production of macrophages were decreased upon treatment with hyphal cells compared with yeast, and depended on the length of hyphae. In summary, the yeast and hyphae forms of C. albicans resulted in an induction of different PRRs, with accompanying differences in immune cell cytokine profiles.

The symbiotic recapture of nitrogen from dead mycorrhizal and non-mycorrhizal roots of tomato plants

AbstractAimsThe aim was to quantify the nitrogen (N) transferred via the extra-radical mycelium of the arbuscular mycorrhizal fungusGlomus intraradicesfrom both a dead host and a dead non-host donor root to a receiver tomato plant. The effect of a physical disruption of the soil containing donor plant roots and fungal mycelium on the effectiveness of N transfer was also examined.MethodsThe root systems of the donor (wild type tomato plants or the mycorrhiza-defectivermcmutant tomato) and the receiver plants were separated by a 30 μm mesh, penetrable by hyphae but not by the roots. Both donor genotypes produced a similar quantity of biomass and had a similar nutrient status. Two weeks after the supply of15 N to a split-root part of donor plants, the shoots were removed to kill the plants. The quantity of N transferred from the dead roots into the receiver plants was measured after a further 2 weeks.ResultsUp to 10.6 % of donor-root15N was recovered in the receiver plants when inoculated with the arbuscular mycorrhizal fungus (AMF). The quantity of15N derived from the mycorrhizal wild type roots clearly exceeded that from the only weakly surface-colonisedrmcroots. Hyphal length in the donorrmcroot compartments was only about half that in the wild type compartments. The disruption of the soil led to a significantly increased AMF-mediated transfer of N to the receiver plants.ConclusionsThe transfer of N from dead roots can be enhanced by AMF, especially when the donor roots have been formerly colonised by AMF. The transfer can be further increased with higher hyphae length densities, and the present data also suggest that a direct link between receiver mycelium and internal fungal structures in dead roots may in addition facilitate N transfer. The mechanical disruption of soil containing dead roots may increase the subsequent availability of nutrients, thus promoting mycorrhizal N uptake. When associated with a living plant, the external mycelium ofG. intraradicesis readily able to re-establish itself in the soil following disruption and functions as a transfer vessel.

Relationships between the litter colonization by saprotrophic and arbuscular mycorrhizal fungi with depth in a tropical forest

Fungal colonization of litter has been described mostly in terms of fructification succession in the decomposition process or the process of fungal ligninolysis. No studies have been conducted on litter colonization by arbuscular mycorrhizal fungi (AMF) and their relationship with the presence of saprotrophic fungi. The aim of the present study was to evaluate the relationships that exist in simultaneous leaf litter colonization by AMF and saprotrophic fungi and the relationships between rates of litter and associated root colonization by AMF at different soil depths. We selected Eugenia sp. and Syzygium sp. in a riparian tropical forest, with an abundant production of litter (O horizon), we evaluated litter and root colonization at different depths, its C:N ratios, and the edaphic physico-chemical parameters of the A horizon immediately below the litter layer. Litter colonization by saprotrophic fungi and AMF increased with depth, but the saprotrophic fungal colonization of some litter fragments decreased in the lowermost level of the litter while AMF litter colonization continued to increase. Plant roots were present only in the middle and bottom layers, but their mycorrhizal colonization did not correlate with litter colonization. The external hyphae length of AMF is abundant (ca. 20 m g−1 sample) and, in common with sample humidity, remained constant with increasing depth. We conclude that in zones of riparian tropical forest with abundant sufficient litter accumulation and abundant AMF external hyphae, the increase in litter colonization by AMF with depth correlates to the colonization by saprotrophic fungi, but their presence in the deepest layers is independent of both litter colonization by saprotrophic fungi and root colonization by AMF.

菌丝室接种解磷细菌Bacillus megateriumC4对土壤有机磷矿化和植物吸收的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 菌丝室接种解磷细菌Bacillus megaterium C4对土壤有机磷矿化和植物吸收的影响 DOI: 10.5846/stxb201106170826 作者: 作者单位: 中国农业大学,中国农业大学,中国农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(31071871,30890132) The effects of inoculation with phosphate solubilizing bacteria Bacillus megaterium C4 in the AM fungal hyphosphere on soil organic phosphorus mineralization and plant uptake Author: Affiliation: China Agriculture University,China Agriculture University,China Agriculture University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:通过30 μm尼龙网将根盒分成根室和菌丝室,菌丝室中的低磷土壤施加75 mg P /kg土壤的植酸钙,研究了菌丝室土壤中丛枝菌根(AM)真菌Glomus intraradices和解磷细菌Bacillus megaterium C4对有机磷的矿化和吸收。结果表明,在试验条件下,植酸钙的溶解性很低,对土壤溶液有机磷的贡献不大。接种解磷细菌C4提高了土壤中磷酸酶的活性,减少了土壤中有机磷的含量。但是,由于存在解磷细菌与AM真菌对磷的竞争,解磷细菌矿化出的磷大部分被自身利用,AM真菌的生长受到抑制,解磷细菌对植物磷营养的改善没有表现出显著的贡献。 Abstract:To study the interactions between arbuscular mycorrhizal (AM) fungus and phosphate solubilizing bacteria (PSB) and their effects on soil organic phosphorus (P) utilization in the hyphal compartment soil, maize (Zea myas L.) plants were grown 8 weeks in sterilized soil (brunisolic soil) in a two compartmented rhizoboxes. The rhizobox was composed of a compartment for root growth (root compartment) and a compartment separated from the root compartment by 30 μm nylon mesh, which can allow the fungal hyphae penetration but prevent the root from growing through (hyphal compartment). Glomus intraradices was inoculated in root compartment of all rhizoboxes. PSB Bacillus megaterium C4 at the concentration of 108 CFU/mL were inoculated in the hyphal compartment. Each rhizobox received 20 mg P/kg of KH2PO4 in the root compartment and 75 mg P/kg of phytin in the hyphal compartment. The results showed that inoculation with PSB C4 in the hyphal compartment soil had no significant influence on mycorrhizal colonization but decreased hyphal length density. The pH in AM treatment was higher than that in the control treatment but close to C4 treatment. The phosphatase activity in AM treatment was similar to the control treatment but significantly lower than that in C4 treatment. NaHCO3 extractable organic and inorganic P contents in AM treatment were similar to those in the control treatment. But both of them decreased significantly in C4 treatment. The biomass and P content of maize in AM treatment were much higher than those in the control treatment, but similar to C4 treatment. The results showed that NaHCO3 extractable organic P content in the hyphal compartment after experiment was 4.4 mg P/kg in the control treatment which was close to the initial soil content of 3.9 mg P/kg. Neither inoculation with AM fungus nor PSB C4 increased the P content, indicating that the solubility of phytin under the experimental condition was lower and didn't have significant contribution to the soil effective organic P. By supplying NO3--N in the hyphal compartment soil, AM fungi raised soil pH but had no influence on the phoshpatase activity. Inoculation with C4 increased phosphatase activity but didn't change soil pH, indicating that C4 added the mount of phosphatase in the hyphal compartment soil. The NaHCO3 extractable organic P content in C4 treatment was much lower than that in AM treatment. NaHCO3 extractable inorganic P content in the C4 treatment soil was also significantly lower than that in the AM treatment but the total P content of maize didn't increase. The hyphal length density decreased after inoculation with C4, and the number of C4 was 5×106 CFU/g soil, indicating that the soil must have provided it with P. So the bacterium C4 immobilized part of soil P to decrease the P uptake by AM fungal hyphae. As a result, the hyphae length density may decrease and P uptake of maize may not increase after inoculation with PSB C4. 参考文献 相似文献 引证文献

Lipid content disturbance in the arbuscular mycorrhizal, Glomus irregulare grown in monoxenic conditions under PAHs pollution

Most polycyclic aromatic hydrocarbons (PAHs) are ubiquitous natural and/or anthropogenic pollutants that have adverse effects on the human health and the environment. Little is known about their potential effects on arbuscular mycorrhizal fungi (AMF). Thus, using monoxenic cultures, this work aims to study the impact of increasing concentrations (140 and 280 μM) of two PAHs [anthracene and benzo[a]pyrene (B[a]P)] on Glomus irregulare lipid content in relation with its development. Changes in the total lipids [fatty acids (FA), sterols, phospholipids (PL) and their associated FA (PLFA)] compositions and contents as well as [malondialdehyde (MDA)] production, of the AMF G. irregulare were examined. Direct toxic effects of both PAHs on the AMF were shown as compared to the control culture. The extraradical hyphae length and spore production were drastically restricted in the presence of PAHs. Significant decreases of the main membrane constituents, phosphatidylcholine (PC) and sterols (in particular 24-methycholesterol) were shown in G. irregulare grown under PAHs treatment. Moreover, PAHs exposure caused an oxidative stress in the AMF extraradical structures pointed out by an increase of the lipid peroxidation biomarker production (MDA). All the observed changes were less marked in presence of anthracene, which was found to be less toxic than B[a]P. Taken together, our results suggested that the drastic decrease of the AMF growth under PAHs pollution could partially be explained by depletions in sterols, PC and MDA accumulation.

Contributions of biotic and abiotic factors to soil aggregation across a land use gradient

Soil aggregation is a major ecosystem process that can be impacted by intensified land use directly through soil disturbances, or indirectly through impacts on biotic and abiotic factors that affect soil aggregation. We collected soils from 27 grassland sites across a range of land use intensities including varying levels of mowing, grazing, and fertilization in order to test the importance of selected direct and indirect effects on soil aggregation. We measured root length and mass, root colonization by arbuscular mycorrhizal fungi (AMF), extraradical AMF hyphal length, soil aggregation, and soil hydrophobicity. We also quantified levels of phosphorus, nitrogen, organic carbon, carbonate carbon, and sand in the soil. As land use intensity (defined as a multivariate index combining mowing, grazing, and fertilization intensities) increased, root mass decreased and length of extraradical hyphae increased. Total colonization by AMF was unaffected by land use intensity, but vesicular colonization tended to increase while arbuscular colonization declined. Soil aggregation increased with increasing land use intensity. We used structural equation models to explore mechanisms of soil aggregation and found that extraradical AMF hyphal length contributed to soil aggregation in models containing only biotic explanatory factors. When we also included abiotic factors in the model, no biotic factor was significant, and soil aggregation decreased as levels of sand and carbonate increased, likely due to concurrent decreases in levels of clay in the soil. In summary, we have shown that agricultural measures such as mowing, grazing, and fertilization can increase soil aggregation in managed grasslands. Furthermore, abiotic factors can be more important for determining soil aggregation than biotic factors, especially in highly aggregated soils. Aggregate turnover may be reduced in such highly aggregated soils past the point required to ensure efficient integration of new labile C into stable aggregates. ► Root length decreased with increasing land use intensity (LUI). ► Extraradical hypha length of arbuscular mycorrhizal fungi went up as LUI increased. ► Soil aggregation increased with increasing LUI. ► Abiotic factors were more important that biotic factors for structuring soils.

The effect of Baccharis glutinosa extract on the growth of mycotoxigenic fungi and fumonisin B1 and aflatoxin B1 production

The aim of this study was to evaluate the effect of Baccharis glutinosa isolated extract on the growth of Aspergillus flavus and Aspergillus parasiticus, and their aflatoxin B1 production; and growth of Fusarium verticillioides, and their fumonisin B1 production. The three fungi were exposed to an antifungal fraction, designated as fraction F6-1, isolated from B. glutinosa by methanolic extraction followed by silica gel chromatography. The growth of the fungi was evaluated in kinetics of radial extension growth, kinetics of spores germination, length and diameter of hyphae, spores diameter, as well as in aflatoxin B1 and fumonisin B1 production. Fraction F6-1 caused radial growth inhibition of the three fungi mainly F. verticillioides. Spores germination of A. flavus and A. parasiticus was delayed in the early stage of the incubation time, although they completely germinated at 27 h. In contrast, spore germination of F. verticillioides was inhibited 87.7% up to 96 h. The lengths and diameters of hyphae, and spore diameters of the three fungi, were significantly smaller in comparison with those of the controls, and several morphological alterations were observed. Concerning aflatoxin B1 and fumonisin B1, fraction F6-1 did not show any inhibition effect at the concentration used. Fraction F6-1 was able to significantly inhibit the development of the three fungi, mainly F. verticillioides. The strong inhibitory effect of F6-1 on hyphae and spores suggests that it interacted with the fungi cell walls, which caused severe deformities. Nevertheless, this fraction was unable in inhibiting mycotoxin production from the three fungi at the concentration tested.

Morphological characterization of the growing front of Rhizopus oligosporus in solid media

Rhizopus oligosporus is used to prepare tempeh and is formed by hyphae which grow as a complex branched structure with irregular borders. The objective of this research was to characterize the macro and micro structural development of R. oligosporus colonies growing on solid media in Petri dishes through image processing and fractal dimension. Stereomicroscope images of the colony were used to detecting the zone in which the fractal dimension (FDE) of the edge (growing front) of the colony represented 97% of the maximum FDE for the 80% of the image of the border. Evaluated characteristics were: radial growth, number of tips in the growing front and the average length of hypha. Two simultaneous events of different and oscillating magnitude were detected in the growing front: branching and increase of the average hypha length. Biomass had a good correlation with radius of the colony, fractal dimension of texture (FDT) and number of tips in the border.

Effect of culture medium composition on Trichoderma reesei’s morphology and cellulase production

The objective of this study was to determine how fungal morphology influences the volumetric cellulase productivity of Trichoderma reesei cultured in four media with lactose and lactobionic acid as fed-batch in a 7 L stirred tank bioreactor. The use of a cellulose–yeast extract culture medium yielded the highest enzyme production with a volumetric enzyme activity of 69.8 U L −1 h −1, and a maximum fungal biomass of 14.7 g L −1. These findings were associated with the following morphological characteristics of the fungus: total mycelia was 98% of total mean projected area, mean hyphae length of 10 mm, mean hyphae volume of 45.1 mm 3, mean hyphae diameter of 7.9 μm, number of branches 9, and number of tips per hypha 29. A positive correlation was found between the total mycelia, the number of tips and the volumetric enzyme productivity, indicating the weight of these variables on the enzyme productivity.

Mycorrhization alleviates benzo[a]pyrene-induced oxidative stress in an in vitro chicory root model

Among chemicals that are widely spread both in terrestrial and aquatic ecosystems, benzo[a]pyrene is a major source of concern. However, little is known about its adverse effects on plants, as well as about the role of mycorrhization in protection of plant grown in benzo[a]pyrene-polluted conditions. Hence, to contribute to a better understanding of the adverse effects of polycyclic aromatic hydrocarbons on the partners of mycorrhizal symbiotic association, benzo[a]pyrene-induced oxidative stress was studied in transformed Cichorium intybus roots grown in vitro and colonized or not by Glomus intraradices. The arbuscular mycorrhizal fungus development (colonization, extraradical hyphae length, and spore formation) was significantly reduced in response to increasing concentrations of benzo[a]pyrene (35–280 μM). The higher length of arbuscular mycorrhizal roots, compared to non-arbuscular mycorrhizal roots following benzo[a]pyrene exposure, pointed out a lower toxicity of benzo[a]pyrene in arbuscular mycorrhizal roots, thereby suggesting protection of the roots by mycorrhization. Accordingly, in benzo[a]pyrene-exposed arbuscular mycorrhizal roots, statistically significant decreases were observed in malondialdehyde concentration and 8-hydroxy-2′-desoxyguanosine formation. The higher superoxide dismutase activity detected in mycorrhizal chicory roots could explain the benzo[a]pyrene tolerance of the colonized roots. Taken together, these results support an essential role of mycorrhizal fungi in protecting plants submitted to polycyclic aromatic hydrocarbon, notably by reducing polycyclic aromatic hydrocarbon-induced oxidative stress damage.

Hydrolase activity as an indicator of the state of microbial communities in vermicomposts

The hydrolase activity was studied using the fluorescein diacetate (FDA) hydrolysis assay in order to assess the microbial activity in composts and vermicomposts obtained with participation of Eisenia fetida andrei, Aporrectodea caliginosa, and A. rosea earthworms from cattle manure, leaves, and peat. The hydrolase activity (the Michaelis—Menten constant, K m ) was found to be lower in the vermicomposts than in the composts and correlated with a corresponding decrease in the length of fungal hyphae. The determination of the hydrolase activity according to the reaction of FDA hydrolysis may be recommended to control the process of vermicomposting and the quality of vermicomposts. Thus, the process of vermicomposting may be characterized with the use of the functional (hydrolase activity) and structural (microbial biomass, length of fungal hyphae) approaches.

Arbuscular mycorrhizal fungi ameliorate temperature stress in thermophilic plants

Biotic interactions can affect the distribution of species across environmental gradients, and as air and soil temperatures increase, plant community response may depend on interactions with symbionts. We measured the effect of elevated soil temperatures on mycorrhizal function and on the response of both plant and fungal symbionts, using fungal inoculum isolated from either high-temperature thermal or nonthermal grassland soils. Our source for thermal soils was Yellowstone National Park, USA, where plants experience rooting zone temperatures of 45 degrees C or more. In the greenhouse, we grew three plant species (Dichanthelium lanuginosum, Agrostis scabra, and Mimulus guttatus) with three arbuscular mycorrhizal fungal (AMF) treatments (no AMF, nonthermal AMF, thermal AMF) and two soil temperatures (ambient, elevated). Biomass of the facultative thermal plants Agrostis scabra and Mimulus guttatus decreased by 50% in elevated-temperature soils, and AMF had no effect on measured plant traits. In contrast, the biomass and total root length of the obligate thermal plant Dichanthelium lanuginosum were greater at elevated soil temperatures, but only when mycorrhizal. Both mycorrhizal colonization levels and length of extraradical hyphae (ERH) increased with soil temperature across all host species. The source of the AMF inoculum, on the other hand, did not affect colonization level, ERH length, host plant biomass, or flowering for all host species in either temperature treatment, suggesting that AMF from thermal soils are not specifically adapted to higher temperatures. In the field we collected soil cores to measure in situ depth distributions of D. lanuginosum roots and ERH, and to determine which AMF species were active in plants growing in thermal soils. Roots were limited to soils with an average temperature < or =30 degrees C, while ERH existed in the hottest soils we sampled, averaging 35 degrees C. Molecular analyses of roots indicated that thermal AMF communities were composed of both generalist and possibly unique fungal species. The increase in host plant allocation to AMF, apparent lack of temperature adaptation by AMF, and differential host response to AMF suggest that AMF could be significant drivers of plant community response to increased soil temperature associated with global change.

Mycorrhizal Hyphal Length as a Function of Plant Community Richness and Composition in Restored Northern Tallgrass Prairies (USA)

We assessed the total length of external arbuscular mycorrhizal hyphae as a function of plant species and functional form richness in restored northern tallgrass prairies. Total hyphal length increased with species and functional form richness. Hyphal length also increased when plant communities were dominated by species with high root density, high root to shoot ratios, and high nitrogen use efficiency. Hyphal length was positively correlated with the biomass of late successional C 4 grasses ( Andropogon gerardi Vitman, Panicum virgatum L., Schizachyrium scoparium [Michx.] Nash-Gould, and Sorghastrum nutans L.), which are obligately mycorrhizal and characterized by high root to shoot ratios, and high root surface area per unit of root biomass. We thus conclude that in order to recover extraradical arbuscular mycorrhizal hyphal length in restored northern tallgrass prairies, at least three factors need to be given priority: 1) achieving high levels of species and functional form richness; 2) making sure that late successional C 4 grasses are present; and 3) making sure that the seed mixture includes species that are characterized by high root to shoot ratio, high root density, and high nitrogen-use efficiency. En este experimento evaluamos la relacion entre la longitud externa del micro micelio arbuscular simbiotico (mycorrhiza) y la diversidad de especies y formas funcionales de plantas en una pradera alta restaurada en el norte de los Estados Unidos. La longitud total del micro micelio subio con el incremento en la diversidad de especies y formas funcionales de plantas. La longitud total del micro micelio tambien subio cuando la comunidad de plantas estaba dominada por especies caracterizadas por una elevada densidades the raices, altas proportion de raices, y alta eficiencia en el uso del nitrogeno. Econtramos tambien que la longitud total del micro micelio estaba correlacionada con la biomasa de herbajes C 4 tipicas del los finales estados de sucesion en estas praderas ( Andropogon gerardi Vitman, Panicum virgatum L., Schizachyrium scoparium [Michx.] Nash-Gould, y Sorghastrum nutans L.). Estos herbajes se caracterizan por ser dependientes en micelio arbuscular simbiotico, altas proporciones de raices, y superficie de raices por unidad the masa de raices. Concluimos que para reestablecer adquados niveles de micro micelio arbuscular simbiotico en las praderas altas del norte de los Estados Unidos al menos tres elementos son necesarios: 1) altos niveles de diversidad the especies y formas funcionales de plantas; 2) la presencia de herbajes C 4 tipicas del los finales estados de sucesion; y 3) asegurar que la mesclas de especies plantadas incluye especies caracterizadas por una alta proporcion de raices, alta densidad de raices, y alta efeciencia en la utilizacion del nitrogeno.

Adaptation of fine roots to annual fertilization and irrigation in a 13-year-old Pinus pinaster stand

Effects of fertilization and irrigation on fine roots and fungal hyphae were studied in 13-year-old maritime pine (Pinus pinaster Aït. in Soland), 7 years after the initiation of the treatments. The fertilization trials consisted of a phosphorus treatment, a complete fertilizer treatment (N, P, K, Ca and Mg), and an unfertilized treatment (control). Fertilizers were applied annually and were adjusted according to foliar target values. Two irrigation regimes (no irrigation and irrigation of a set amount each day) were applied from May to October. Root samples to depths of 120 cm were collected in summer of 2005, and the biomass of small roots (diameter 2-20 mm) and fine roots (diameter </= 2 mm) and fine root morphology were assessed. Biomass and length of hyphae were studied by a mesh ingrowth bag technique. Total fine root biomass in the litter and in the 0-120 cm soil profile ranged between 111 and 296 g m(-2). Results derived from the measurements of biomass and root length, or root area, showed that both fertilizer treatments reduced the size of the fine root system, especially in the top soil layers, but did not affect small roots. Compared with control treatments, fine root morphology was affected by both fertilizer treatments with the fine roots having increased specific root length/area, and irrigation tended to reinforce this finer morphology. The amount of hyphae in the mesh ingrowth bags was higher in the fertilization and irrigation treatments than in the controls, suggesting further extension of the root system (ectomycorrhizal infection) and thus of the uptake system. Irrigation had no significant effect on the size of the fine root system, but resulted in a shallower rooting system. Total root to shoot ratios were unaffected by the treatments, but fine root mass:needle mass and fine root area index:leaf area index ratios decreased with increasing nutrient supply. Overall, compared with the control fine roots, increased nutrient supply resulted in a lower fine root biomass but the dynamic fraction of the finest roots was greater. Irrigation had only limited effects on fine root size, distribution and morphology.

Distribution of bacterial and fungal populations between water-dispersed soil components and water-stable soil aggregates determined using the partial-sterilization and wash-sonic methods

We investigated the effects of long-term cattle slurry application on soil aggregation and the distribution of microbial populations by characterizing soil structural properties, extraction patterns of chloroform-labile carbon over increasing periods of fumigation and microbial direct counts using the wash-sonic method in soil samples from an upland field with three levels of slurry application, 60, 150 and 300 Mg ha−1. The soil samples could be categorized based on the extraction patterns of chloroform-labile carbon. Soil from the 60 Mg ha−1 plot released carbon at a constant rate under chloroform fumigation for 0.5 and 24 h. The chloroform-labile carbon in the 300 Mg ha−1 plot significantly increased over the same period, while that in the 150 Mg ha−1 plot increased for 1 h only. The bacterial count and the overall length of fungal hyphae were similar in the three plots. Indirect assessments of the relative abundance of bacterial and fungal populations using the wash-sonic method suggested that water-stable soil aggregates in the 300 Mg ha−1 plot were stabilized by hyphae to a higher degree than aggregates from the 60 and the 150 Mg ha−1 plots. The bulk densities significantly decreased and the maximum water-holding capacity significantly increased with the slurry application level. These observations confirm that slurry application enhances water-stable soil aggregation. A combined approach using the partial-sterilization and wash-sonic methods revealed that the relative dominance of fungal populations in the water-stable soil aggregates resulted in a higher amount of labile carbon in the time-dependent extraction by chloroform in the 300 Mg ha−1 plot compared with the 60 and 150 Mg ha−1 plots. The wash-sonic method has the potential to characterize microbial distribution between water-dispersed soil components and water-stable soil aggregates.

Disruption of Trichoderma reesei gene encoding protein O-mannosyltransferase I results in a decrease of the enzyme activity and alteration of cell wall composition.

In fungi transfer of the first mannosyl residue to proteins during their O-glycosylation is catalyzed by protein O-mannosyltransferases encoded by pmt genes. Disruption of the pmt1 gene in Trichoderma caused a significant decrease in the total activity of protein O-mannosyltransferases. Moreover, disruption of the pmt1 gene also led to osmotic sensitivity of the strain, indicating an essential role of the PMTI protein activity for cell wall synthesis. At the same time, the strain was defective in septa formation, producing only half the number of septa per unit length of hypha compared with the wild type. Disruption of the pmt1 gene decreased protein secretion but had no effect on glycosylation of secreted proteins, which suggests that PMTI protein O-mannosyltranferase does not take part in glycosylation of these proteins.

Effect of Paenibacillus alvei, strain K165, on the germination of Verticillium dahliae microsclerotia in planta

Verticillium wilt is a devastating disease of a wide range of herbaceous and woody plant hosts, incited by the soilborne fungus Verticillium dahliae. In the present study, the effect of the potential biocontrol isolate Paenibacillus alvei, strain K165, on the germination of V. dahliae microsclerotia (msc) was investigated. Strain K165 was isolated from tomato root tips and its activity against V. dahliae has been shown in glasshouse and field experiments. In the present study, the application of K165 resulted in the reduction of msc germination of V. dahliae, in the root tips and the zone of elongation, of eggplants by 50% compared to the control treatment; whereas 10 and 12 cm away from root tips and in soil without plants the percentage of msc germination was reduced by 26% and 40%, respectively. However, K165 did not significantly affect the number and length of hyphae per germinated msc. In a split-root system, K165 triggered induced systemic resistance in eggplants against V. dahliae by reducing disease severity and msc germination by 27% and 20%, respectively. In addition, K165 colonised the rhizosphere of eggplants and soil in a population density of 5 and 3 log 10 cfu g −1, 7 dpi, respectively. This is the first report of evaluating the direct/indirect effect of a rhizospheric bacterium on msc germination in the rhizosphere of eggplants, indicating that strain K165 reduces msc germination.

Effect of tetracycline on the colonization and growth of microbes on Scirpus lacustris litter in oligotrophic and eutrophic waters

Studies of microbes on Scirpus lacustris submerged in river (oligotrophic) and wetland (eutrophic) waters were conducted to determine how nutrient status affected colonization and growth on the same substrate. The antibiotic tetracycline was used to repress bacteria to determine if they inhibited fungal growth. The use of tetracycline was also relevant in a broader context as antibiotics are now being detected in aquatic systems. Dead S. lacustris stems were submerged for 33 d in natural and tetracycline amended (500 and 4000 µg l -1 ) river and wetland waters. Confocal laser scanning microscopy was used to scan the biofilm while image analysis was used to determine microbial (algal, bacterial, fungal) cell volume and fungal biomass by measuring the length of fungal hyphae. In all treatments, microbial cell volume peaked on Day 10 and was greater (ANOVA, all p 0.05). On Day 10, the controls of both water treatments had significantly greater microbial biovolume than both the 500 and 4000 µg l -1 antibiotic treatments (both p = 0.02), indi- cating that tetracycline had a negative effect on microbes colonizing Scirpus.

Organic matter and soil tilth in arable farming: Management makes a difference within 5–6 years

Management-induced depletion in soil organic carbon (SOC) may create critical tilth conditions for arable farming. We investigated the short-term effect of crop rotation and addition of animal manure on SOC fractions, the dispersibility of soil clay, the length of fungal hyphae, wet aggregate stability, tensile strength of dry aggregates, and the pore size distribution, gas diffusivity and permeability of undisturbed bulk soil. SOC fractions were measured in whole-soil samples and in 1–2 mm air-dried aggregates. Plough layer soil was sampled 5 and 6 years after the start of a field experiment with different cropping systems at two loamy sand soils (Foulum, ∼9% clay and Flakkebjerg, ∼14% clay). A soil drop test was performed in the field to evaluate in situ soil friability. A system dominated by small grain cereals not receiving animal manure served as a reference treatment (‘CEREAL’). This system was compared to the same crop sequence but with application of animal manure (‘CEREAL + MANURE’, only at one location), and to a diversified crop rotation including grass/clover but without addition of animal manure (‘CEREAL + GRASS’). A part of each field plot was compacted by a medium-sized tractor. The content of SOC was lowest for the CEREAL system at both locations. Hot-water extractable SOC displayed the same pattern. The carbon fractions in aggregates responded similarly to cropping systems as those in whole-soil samples. Clay dispersibility was highest in the CEREAL system. The length of fungal hyphae was enhanced by the versatile crop rotation. Soil compaction tended to increase clay dispersibility. Our results confirmed agronomic observations that the tilth in the Flakkebjerg soil was problematic and worse than in the Foulum soil, but generally only trends were found in amelioration of the poor mechanical tilth characteristics. In contrast, soil (macro)porosity was significantly higher for the CEREAL + GRASS system compared to the other two systems, and the CEREAL + MANURE and CEREAL + GRASS systems had more tortuous pore systems compared to the CEREAL system and better resisted compaction than the latter. We conclude that only 5–6 years of differentiated soil management significantly affected SOC fractions, the dispersibility of clay, and the growth of fungal hyphae. As only trends were found in the mechanical aspects of soil tilth, the tilth-forming agents may serve as early indicators of changes in soil tilth. Our results also indicate that soil pore characteristics are affected by short-term management and probably provide the basis for later significant changes also in mechanical tilth characteristics.

Colonization, ALP activity and plant growth promotion of native and exotic arbuscular mycorrhizal fungi at low pH

Soil acidity can affect arbuscular mucorrhizal fungi (AMF) in many aspects. In this study, by inoculating white clover ( Trifolium ripens L.) with AMF at two pH levels (pH 5.0 and 6.0), we investigated the influences of low pH on the colonization, alkaline phosphatase (ALP) activity and promoting effect of AMF, and also compared the different responses of native AMF community and exotic species ( Gigaspora margarita) to low pH. PCR-DGGE profiles revealed the obvious difference in native AMF community structure between low and high pH. Compared to low pH, high pH decreased the total and vesicle colonization, external hyphae length density of native AMF, but exerted no effect on those of exotic AMF. For both native and exotic AMF, high pH enhanced the proportions of arbuscule and fungal structure with ALP activity in colonized roots. Both native and exotic AMF promoted the shoot biomass, with greater increase at low pH than at high pH. Plant growth was more dependent on exotic AMF than on native AMF at both pH levels. The same trends were observed in P uptake as in biomass. Our study suggested that the increase in pH can exert inhibitory effects on AMF species native to acidic soil, including ecological (community structure), functional (ALP activity) and developmental (hyphal length, vesicle and arbuscule percentage, total colonization) aspects, but have no effect on exotic species in the present experiment.