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1.
Transverse sections of lesioned tissue taken from wheat roots grown in soil naturally infested with Gaeumannomyces graminis var, Tritici were stained with trypan blue and the area of stele occupied by hyphae or by brown host deposits was measured. The area of mycelium in lesioned pieces taken from seedling or tillering plants and used as inoculum in host infectivity tests was positively correlated with the disease produced and the area of brown deposits in lesioned pieces taken from tillering or mature plants was negatively correlated. Whole pieces of lesioned tissue were examined cytochemically for glutamic and succinic dehydrogenases in the invading hyphae. Groups of host cells in the endodermal region were filled with hyphae showing positive reactions for both dehydrogenases (active) and separated by areas of brown discoloured host tissue containing few active hyphae. Less than half the discoloured lesion was occupied by active hyphae. The area of lesion containing hyphae with dehydrogenase enzymes was positively correlated with the measure of disease severity of the roots and with the infectiveness of the lesioned tissue when inoculated on to axenic wheat seedlings. The progress of infection in axenie seedlings inoculated at 3 or 8 cm from the seed differed with the two placements, notably in the host response and the growth of active hyphae in the cortex.  相似文献   

2.
The effect of clear-cutting on fluorescein diacetate (PDA) active and total fungal biomass was studied in three soil horizons of a coniferous forest in Sweden. Throughout the soil profile, fungal biomass decreased after felling. FDA-active hyphae decreased more in the mineral soil than in the organic soil. The effect of felling residues left at the time of clear-cutting appeared to be of only minor importance, since the decrease in fungal content was independent of the amount of slash left on the ground. However, the addition of slash generally gave greater amounts of FDA-active fungal mycelium compared to the treatment without slash. The change in root dynamics is suggested to be an important reason for the decrease of fungal hyphae in forest soil after clear-cutting.  相似文献   

3.
Arbuscular mycorrhizal fungi (AMF) differ in their rate and extent of colonization of both plant roots and soil but the mechanism responsible for these differences is unclear. We compared the external mycelium of three AMF isolates (Glomus intraradices, Glomus etunicatum and Gigaspora gigantea) during early colonization of plant roots. We investigated whether an AMF with the most rapid colonization would have higher numbers of infective structures (i.e., infection hyphae and contact points), an AMF with extensive root colonization would have more infection units, and (3) AMF with extensive soil colonization would have large numbers of all external features (including absorptive hyphae, runner hyphae and hyphal bridges). Using specially designed soil and root observation chambers, we followed the development of the external mycelium for 7 weeks. We found that rapid colonization rate was due, in part, to the presence of more infective structures, in particular more infection hyphae and root contact points. Second, the extensive root colonizer had more, larger infection units. Third, data did not support the hypothesis that the extensive soil colonizer had more external structures. These results show that differences in the architecture of the external mycelium are responsible, in part, for variation in the colonization strategy of AMF.  相似文献   

4.
Arbuscular mycorrhizal fungi (AMF) produce a protein, glomalin, quantified operationally in soils as glomalin-related soil protein (GRSP). GRSP concentrations in soil can range as high as several mg g−1 soil, and GRSP is highly positively correlated with aggregate water stability. Given that AMF are obligate biotrophs (i.e. depending on host cells for their C supply), it is difficult to explain why apparently large amounts of glomalin would be produced and secreted actively into the soil, since the carbon could not be directly recaptured by the mycelium (and benefits to the AMF via increased soil structure would be diffuse and indirect). This apparent contradiction could be resolved by learning more about the pathway of delivery of glomalin into soil; namely, does this occur via secretion, or is glomalin tightly bound in the fungal walls and only released after hyphae are being degraded by the soil microbial community? In order to address this question, we grew the AMF Glomus intraradices in in vitro cultures and studied the release of glomalin from the mycelium and the accumulation of glomalin in the culture medium. Numerous protein-solubilizing treatments to release glomalin from the fungal mycelium were unsuccessful (including detergents, acid, base, solvents, and chaotropic agents), and the degree of harshness required to release the compound (autoclaving, enzymatic digestion) is consistent with the hypothesis that glomalin is tightly bound in hyphal and spore walls. Further, about 80% of glomalin (by weight) produced by the fungus was contained in hyphae and spores compared to that released into the culture medium, strongly suggesting that glomalin arrives mainly in soil via release from hyphae, and not primarily through secretion. These results point research on functions of glomalin and GRSP in a new direction, focusing on the contributions this protein makes to the living mycelium, rather than its role once it is released into the soil.  相似文献   

5.
Several ectomycorrhizal fungi, including Hebeloma cylindrosporum, actively release large quantities of phosphatase enzymes into their growth medium. We fractionated the phosphatase activity of the ectomycorrhizal association between H. cylindrosporum and its host plant, Pinus pinaster, with the aim to quantify its spatial and temporal variation in response to contrasting soil phosphorus conditions. Seedlings were grown in mini-rhizoboxes and the phosphomonoesterase activity of rhizosphere soil, released by roots, surface-bound to roots or mycelium was determined spectrophotometrically with the p-nitrophenyl phosphate method or microscopically with the ELF-method as a function of culture time. We showed that acid phosphatase activity of the soil and the root increased with mycorrhizal association. We also observed that the phosphatase activity associated with ectomycorrhizal plants was related to soil type. All phosphatase fractions decreased over culture time, except the proportion of hyphae exhibiting phosphatase activity in the extramatrical mycelium, which increased over time. The specific fractions of phosphatase activity associated with the mycorrhizal plants were clearly related to the soil phosphorus type and content. Soils showed an increase in acid phosphomonoesterase activity with mycorrhizal association, supporting a role for this enzyme in the degradation of soil bound phosphorus. The gradually increasing proportion of hyphae in the extramatrical mycelium exhibiting alkaline phosphatase activity, particularly under low phosphorus conditions, indicates an induction of alkaline phosphatase activity by phosphorus limitation.  相似文献   

6.
Total length and biomass of fungal mycelium in the soil of a young stand of second-growth Douglas-fir in the central Oregon Coast Range were estimated over 27 months with the agar-film technique. Mycelial mass was at maximum in fall and spring and significantly lower in summer. Melanized hyphae dominated other colors, averaging 66% of monthly litter and 73.7% of soil hyphal weight. The mycorrhizal fungus Cenococcum geophilum Fr. had significantly larger average diameter than other hyphae and contributed from 1.2 to 64.8% of the monthly hyphal volume. Multiple regression analyses with temperature, moisture, and litterfall produced no adequate predictive equations for monthly fungal biomass. Large biomass fluctuations over short periods necessitate frequent sampling and long-term study to fully assess the importance of fungal hyphae in ecosystems.  相似文献   

7.
Budget studies in boreal podzols indicate a considerable upward transport of aluminium (Al) from the mineral soil into the organic horizon. In this paper we studied if ectomycorrhizal (EcM) fungi can be involved in this upward transport via their extramatrical hyphae. We tested the use of gallium (Ga) as proxy for Al. Transport of Al through EcM hyphae was studied in vitro in a two-compartment Petri dish system. Two of the five fungal isolates tested transported Al. Using Ga instead of Al revealed the same trend in these systems, confirming the use of Ga as proxy for Al. Upward transport of Ga was studied in an artificial podzol. Pinus sylvestris seedlings were colonised by a natural community of EcM fungi from fresh forest soil. Gallium addition to the mineral soil led to increased Ga content in roots in the organic horizon and in the shoot. Upward Ga allocation was significantly higher when roots were excluded from the mineral soil by a mesh, only allowing fungal mycelium to grow through. We conclude that at least some EcM fungi transport Al and that Ga, and probably also Al, can be transported upwards by EcM fungal hyphae in a podzol system. These findings support the hypothesis that EcM fungi play a role in upward transport of Al in podzols.  相似文献   

8.
Microbiological investigations of cultural layers were performed in a settlement of the Alanian culture—Podkumskoe-2 (the 2nd–4th centuries AD). The present-day soddy-calcareous soils (rendzinas) used for different purposes were also studied near this settlement. The most significant changes in the initial characteristics of the soil microbial communities occurred under the residential influence more than 1500 years ago; these changes have been preserved until the present time. In the areas subjected to the anthropogenic impact, the total microbial biomass (the weighted average of 3720 μg C/g soil) was lower than that in the background soil. The minimal values of the microbial biomass were found in the soil of the pasture—2.5 times less than in the background soil. The urease activity of the cultural layer was higher than that of the soils nearby the settlement. Elevated values of the cellulose activity were also recorded only in the cultural layers. The current plowing has led to a significant decrease in the mycelium biomass of the microscopic fungi. In the soil of the fallow, the weighted average value of the fungal hyphae biomass along the profile was twice lower than that in the background soil and cultural layers of the settlement. The pasture first affected the active microbial biomass and, to a lesser extent, the amount of microscopic fungi.  相似文献   

9.
Arbuscular mycorrhizal (AM) fungi and phosphate solubilizing bacteria (PSB) have a positive effect on plant productivity primarily through increasing phosphate availability. In order to study the interaction between AM fungi and PSB, we used Bacillus megaterium, a PSB isolated from the sterilized surface of AM germinated spores, and two strains of the AM fungus Glomus intraradices with different mycelial architecture. A greenhouse experiment was designed with maize as host plant with the addition of tribasic calcium phosphate. We tested the hypothesis that PSB, intimately linked with AM fungi, could interact differentially with the two AM strains. We concluded that inoculation with the PSB positively affected maize mycorrhization. Insoluble phosphate alone did not influence the AM extraradical mycelium (ERM) length and maize mycorrhization when bacteria were not inoculated. The results provide evidence that the adverse effect on infectivity for some AM strains might be caused by solubilized phosphorus release to the rhizosphere by PSB. Differences related to the mycelium architecture of each AM strain were observed: the density of PSB in rhizosphere soil was significantly higher only with the GA8 strain coinciding with the highest values of maize biomass. The density of bacteria associated with GA8 mycelium could be the result of the transfer of photosynthates through the rhizosphere; this close contact would favor the persistence of the intimate relationship between PSB and AM hyphae. In the bacteria-free treatments, soil adherence was not significantly altered. Although the highest development of ERM occurred with GA5, plants inoculated with GA8 showed the highest values for soil adherence. This may be due to the AM mycelium which modifies bacterial persistence in the rhizosphere and consequently soil adherence. Our results show that for potential applications, some characteristics of the AM strains are key in the selection of the AM fungi–PSB combinations. These include the tolerance to soluble phosphorus, the rate of root colonization, and ERM development that favors the persistence of bacteria in rhizosphere soil.  相似文献   

10.
Ectomycorrhizal mycelial necromass is an important source of carbon for free-living microorganisms in forest soils, yet we know little either of its fate when it enters soil or of the identity of microbes that are able to utilise mycelium as their energy source. Here we used 13C-labelled mycelium of the ectomycorrhizal fungus Pisolithus microcarpus in laboratory incubations in combination with DNA-stable isotope probing (SIP) to determine the identity of functionally active soil fungi that can utilise dead mycelium. We also used solid-state nuclear magnetic resonance (NMR) spectroscopy to detect parallel changes in the abundance of key biochemical constituents of soil. A decrease in bulk soil 13C concentration together with rapid loss of glycogen and chitin-glucan during the 4 week incubations suggested that dead mycelium was rapidly turned over. Further, 13C was incorporated into fungal DNA within 7 days of addition to soil. DNA-SIP also revealed a dynamic community of functionally active soil fungi. By applying DNA-SIP and NMR in parallel, our data show that carbon from decaying ectomycorrhizal mycelium is rapidly transformed and incorporated into free-living soil fungi. This finding emphasises that dead extra-matrical mycelium is an important source of labile carbon for soil microorganisms.  相似文献   

11.
The ectomycorrhizal mycelium is a large component of boreal and temperate forest soil microbial biomass and the resulting necromass is likely to be an important source of nutrients for saprotrophic microorganisms. Here we test the effects of species richness of ectomycorrhizal mycelial biomass on short-term CO2 efflux by amending forest soil with necromass from 8 fungal species added separately and in mixtures of 2, 4 and 8 species. All additions of necromass rapidly increased soil CO2 efflux compared to unamended controls but CO2 efflux increased significantly with species richness. Efflux of CO2 did not correlate with the carbon (C) or nitrogen (N) contents or the C:N ratio of the added necromass. The study demonstrates that species diversity of dead ectomycorrhizal fungal hyphae can have important consequences for soil CO2 efflux, and suggests decomposition of hyphae is regulated by specific constituents of the nutrient pools in the necromass rather than the total quantities added.  相似文献   

12.
A technique for assessing the metabolically-active fungal biomass by means of fluorescein diacetate (FDA) staining was recently described (Söderström, 1977). In this note some practical details in the application of this technique to studies of FDA-active fungal biomass in the soil are discussed.  相似文献   

13.
Metabolically-active fungal biomass, as determined with fluorescein diacetate (FDA) staining, was studied during a 27-month period (21 samplings) in three horizons of a podzolized pine-forest soil. Recurrent definite biomass peaks were registered in autumn and early spring. Biomass increase was also noted during the winter with soil temperatures below 0°C. Only a minor fraction (2.4–4.3%) of the total fungal biomass was found to be active. The FDA-active biomass m?2 was equally distributed between the organic (5 cm) and mineral (15 cm) soil horizons, and varied between 0.5 and 2.4 g d.w. m?2. The amount of FDA-active biomass was correlated with soil moisture content.  相似文献   

14.
The relationship between fungal activity in soil and staining with fluorescein diacetate (FDA) was investigated using Penicillium citrinum and Rhizoctonia solani inoculated into autoclaved and non-sterilized soil, with or without nutrient amendment. Correlations of fungal activity with FDA staining allowed a quantitative relationship between FDA-staining and fungal CO2-evolution to be calculated. Results suggest that where nutrient fluxes occur in the soil, correlation between FDA-staining and CO2 evolution may be useful in assessing fungal contributions to carbon transformations.  相似文献   

15.
In acidified forest soils, the coarse‐soil fraction is a potential nutrient source. Plant nutrient uptake from the coarse‐soil fraction is aided by ectomycorrhiza. Similarly, (recalcitrant) organic matter (OM) is an important nutrient source largely made plant‐available through (symbiotic) microorganisms, especially in the topsoil. We hypothesized that in a podzol profile, fungal hyphae would concentrate in nutrient hotspots, either OM or the coarse‐soil fraction. Absolute hyphal length, base saturation, and organic‐C content of a Podzol profile were determined in the fine‐earth and coarse‐soil fractions. In the fine‐earth fraction, hyphae were attracted by the organic‐C content and relative high base saturation. In the coarse‐soil fraction of the BhBs horizon, the absolute hyphal length exceeded the hyphal length in the fine earth by factor 3, yet C content and base saturation were lowest. We could not determine to what fungi the hyphae belonged. Most likely ectomycorrhiza, ericoid mycorrhiza and saprotrophic fungi dominate the upper soil layers of this profile and all utilize OM for nutrition. In the deeper mineral horizons and especially in the coarse‐soil fraction, ectomycorrhiza are better adapted than other fungi to harvest nutrients from inorganic sources. Additionally, favorable physical properties may explain the high amount of fungal hyphae in the coarse‐soil fraction of the BhBs horizon. Both the coarse‐soil fraction and deeper mineral soil horizons may play a more active role in microbial nutrient cycling than previously assumed.  相似文献   

16.
We used minirhizotrons to examine the production and turnover of fungal hyphae in situ during the dry season in a Californian grassland. Hyphae were produced relatively slowly throughout the season at rates that did not vary significantly over time, indicating that a portion of the fungal community was active even when soils were very dry. In addition, fungi displayed relatively long residence times, with half of the hyphae remaining in the soil for at least 145 days. Together, these results suggest that a contingent of active fungi may be capable of performing nutrient transformations when plants are otherwise dormant, while relatively long-lasting hyphae may immobilize nutrients for several months before turning over.  相似文献   

17.
In terrestrial ecosystems, plants are frequently in symbiosis with arbuscular mycorrhizal fungi (AMF) with mineral nutrients and photosynthesis carbon exchanges in between. This research sought to identify the effects of phosphorus (P) levels on the nitrogen (N) uptake via extraradical mycelium (ERM) and the mycorrhizal growth response (MGR) of maize plants within the AMF symbiosis. Pots were separated into root compartments and hyphae compartments (HCs) with two layers of a 30‐μm mesh membrane and an air gap in between, where only hyphae could pass through, to avoid both N diffusion and root growth effects. Maize plants were inoculated with Rhizophagus irregularis with different N fertilization in HCs under two different P fertilization levels. Our results indicated that a strong increase in MGR with low‐P fertilization. The same tendency was not observed with high‐P fertilization, although both had a large increase in P concentration as a potential source of growth in shoot tissue of mycorrhizal plants. Substantial effects (10.5% more N) were observed in the case of high‐P availability for the host plants from ERM fed with N, whereas under low‐P conditions ERM may prioritize P uptake rather than N uptake. The AM fungi increase the uptake of N and P, which are most limiting in the soil with fewer forces from soil resources. In addition, there was still more P accumulated than N due to the high N for ERM with high‐P supply. Low N in HCs corresponded with a lower colonization rate in roots but with high hyphae density in HCs; this result suggest that N and P availability might change the ratio of extraradical to intraradical hyphae length.  相似文献   

18.
External arbuscular mycorrhiza (AM) mycelium plays an important role in soil while interacting with a range of biotic and abiotic factors. One example is the soil organic amendment sugar beet waste. The fermented Aspergillus niger-sugar beet waste (ASB) increases growth and P uptake by the AM mycelium in soil whereas non-fermented waste (SB) had a strong inhibitory effect. The underlying mechanisms are not understood.We used gas chromatography-mass spectrometry to identify differences in composition of water extracts of ASB and SB. The chromatograms showed that ferulic acid was present in SB and absent in ASB. We compared the effects of the water extracts of SB and ASB and ferulic acid upon the growth of Glomus intraradices in in vitro monoxenic cultures.Hyphal growth of the AM fungus G. intraradices was extremely reduced in ferulic acid and SB treatments. Moreover, AM hyphae appeared disorganized, undulated and tangled. In contrast, ASB increased hyphal length and numbers of branched absorbing structures and of spores. We conclude that ferulic acid is one compound in SB which is responsible for its inhibition of AM extraradical growth. The relevance of these findings is discussed.  相似文献   

19.
Autoradiographic procedures are described to detect metabolically-active hyphae in litter habitats. Experiments with Sclerotium rolfsii and with hyphae present on the surfaces of leaf litter of beech showed that active hyphae could be detected after exposure for 2 hr to 10 μCi/ml of uniformly-labelled 14C-glucose followed by film exposure for 2 days. Controls indicated that there was negligible background radioactivity and that there was no adsorption or non-metabolic (passive) uptake of radionuclide by hyphae. Liquid photographic emulsion was superior to stripping film because closer contact could be obtained between the hyphae and the emulsion. Use of photographic emulsion was facilitated by removing hyphae from leaf litter surfaces in polystyrene peels and then covering the polystyrene peels with emulsion. The use of these techniques in other habitats in soil is discussed.  相似文献   

20.
A better understanding of the role of glomalin in arbuscular mycorrhizal fungi necessitates knowledge about the cellular functions and locations of this putative heat-shock protein (Hsp). In the present study, we determined the cellular localization of glomalin in mycelium of Glomus intraradices using immuno-electron microscopy, employing the monoclonal antibody MAb32B11. We observed that there were more gold beads bound to hyphae and spore walls than in the cytoplasm. There was also differential binding within the wall layers: L3 and L2 presented more intense labeling than the L1 layer. Our data on wall-binding of glomalin are strongly suggestive of functions other than cytoplasmic (Hsp-related), and point to a possibility of mediating interactions with the biotic and abiotic soil environment.  相似文献   

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