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1.
 To study the effects of omnivory on the structure and function of soil food webs and on the control of trophic-level biomasses in soil, two food webs were established in microcosms. The first one contained fungi, bacteria, a fungivorous nematode (Aphelenchoides saprophilus) and a bacterivorous nematode (Caenorhabditis elegans), and the second one fungi, bacteria, the fungivore and an omnivorous nematode (Mesodiplogaster sp.) feeding on both bacteria and the fungivore. Half of the replicates of each food web received additional glucose. The microcosms were sampled destructively at 5, 9, 13 and 19 weeks to estimate the biomass of microbes and nematodes and the soil NH4 +-N concentration. The evolution of CO2 was measured to assess microbial respiration. Microbial respiration was increased and soil NH4 +-N concentration decreased by the addition of glucose, whereas neither was affected by the food-web structure. Supplementary energy increased the biomass of fungi and the fungivore, but decreased the biomass of bacteria, the bacterivore and the omnivore. The omnivore achieved greater biomass than the bacterivore and reduced the bacterial biomass less than the bacterivore. The biomass of the fungivore was smaller in the presence of the omnivore than in the presence of the bacterivore at three sampling occasions. Fungal biomass was not affected by food-web structure. The results show that the effects of the omnivore were restricted to its resources, whereas more remote organisms and soil processes were not substantially influenced. The results also indicate that the presence of an omnivore does not necessarily alter the control of populations as compared with a food web containing distinct trophic levels, and that the fungal and bacterial channels may respond differently to changes in energy supply. Received: 15 December 1997  相似文献   

2.
The family Tylenchidae is a large group of soil nematodes but their feeding habits are not fully known. We studied the fungal-feeding abilities of nematodes in the genus Filenchus. We measured population growth rates (PGRs) of six nematode isolates, representing three Filenchus species, when feeding on seven fungal species on two types of culture media. On Potato Dextrose Agar (PDA) Filenchus misellus, Filenchus discrepans and an unidentified Filenchus sp. generally showed moderate to large PGRs on saprophytic fungi (Rhizoctonia solani, Chaetomium globosum, Coprinus cinereus, Flammulina velutipes) and low PGRs on plant-pathogenic fungi (Fusarium oxysporum, Pythium ultimum). In soil medium amended with chopped soybean plant material or wheat bran, the status of most of the fungi as food for the nematodes was similar to that on PDA, although PGRs tended to be lower in the soil medium. However, C. globosum, a good food on PDA, only supported low PGR in soil for each of the three nematodes. The PGRs of F. misellus on C. globosum in soil were still low even when types and amounts of organic matter amendments were varied. A nematophagous fungus, Pleurotus ostreatus (oyster mushroom), was determined to be a food for Filenchus on PDA or in soil, based on PGR measurements corrected for extraction efficiency. To determine whether fungal species and culture media affected nematode extraction efficiencies and, consequently, the apparent PGRs, we compared efficiencies between R. solani, C. globosum and C. cinereus, and between PDA and soil. The relatively low extraction efficiencies across fungal species in soil seemed responsible for the lower nematode PGRs in soil than on PDA. On PDA generally, fungal species did not affect the assessment. In soil, effects of fungal species on extraction were significant, but not consistent, across nematode species. Nevertheless, the extraction efficiency differences in soil were considered not to affect assessment of the three fungi as food for the nematodes. The confirmation that three Filenchus species reproduce by feeding on fungi in soil suggests that fungal-feeding is not an unusual habit in the field, in this genus. We believe that in community studies, nematodes in the genus Filenchus should be considered fungal feeders or root and fungal feeders, rather than only plant feeders. Our confirmation of fungal-feeding habits in the genus Filenchus supports the hypotheses that plant-feeding nematodes evolved from those feeding on fungi.  相似文献   

3.
The quality of plant material affects the vigor of the decomposition process and composition of the decomposer biota. Root residues from hairy vetch (Vicia villosa Roth), rye (Secale cereale L.) and vetch+rye, packed in litterbags were placed in pots of soil at 15 C and the content of the bags was analyzed after 2, 4, 8 and 12 weeks. Bacterial biomass did not differ between residues with contrasting composition. Among bacterivores groups of nematodes that require high bacterial production dominated in fast decomposing resources whereas flagellates with smaller requirements prevail in slower decomposing resources. Biomass of bacterial feeding nematodes correlated positively with early phase (0-2 wk) decomposition that increased in the order: rye< vetch+rye<vetch. Bacterial biomass therefore seems to be under top-down (predation) control during early decomposition. In contrast, the fungal biomass differed between resources with highest values for rye. Moreover, this increase in fungal biomass occurred later during succession and was correlated with decomposition activity for rye in that period. Fungal biomass therefore seems to be under bottom-up (resource) control. The composition of the nematode assemblages (composed of 25 taxa) showed a clear relationship to initial plant resource quality as well as decomposition phase. Early successional microbivorous nematodes vary according to resource quality with demanding bacterivores+predators (Neodiplogasteridae) dominating in vetch and less demanding bacterivores (Rhabditidae) and fungivores (Aphelenchus) being equally common in vetch and rye. Later in the succession (2-4 wk) bacterivorous Cephalobidae and fungivorous Aphelenchoides prevailed similarly on the different root materials whereas bacterivorous protozoa and the amoebal fraction thereof dominated in rye. At week 12 no species dominated the nematode assemblages that were similar between the resources. The differences between nematode assemblages among plant resources at 2 week were similar to the results of a field study sampled after 6 weeks with the same soil and plant resources. This lends support to the relevance of the successional patterns observed in this incubation study.  相似文献   

4.
The ongoing research ‘boom’ in soil ecology has been advanced by a widespread use of laboratory experiments to investigate mechanisms that could not be unravelled with field observations alone. Interactions between soil fungi and invertebrates have received considerable attention due to their trophic and functional importance in belowground systems. Saprotrophic cord-forming basidiomycete fungi are major agents of primary decomposition in woodland ecosystems, where they are also an important source of nutrition for fungal-feeding soil invertebrates. A plethora of microcosm experiments, with their main benefit being that they enable most variables to be kept constant while just a few are manipulated, have provided detailed insights into the ecology of fungus–invertebrate interactions. This review identifies important trends from this body of work (including a meta-analysis of grazing effects on fungal growth and wood decomposition) and explores the extent to which these patterns are supported by the few related experiments conducted in more complex mesocosm and field systems. Grazing in microcosms reduced fungal growth and increased decomposition, but with interaction-specific magnitude, reflecting invertebrate feeding preferences for different fungi. Macro-invertebrates (woodlice and millipedes) had stronger effects than micro- (e.g. nematodes) and meso- (e.g. collembola) invertebrates. This greater grazing pressure generally increased enzyme activities beneath mycelia during interactions in which wood decay was increased. Top-down effects of fungal-feeding can be extrapolated to more complex systems, but only for macro-invertebrates, particularly woodlice. Soil enzyme activity was stimulated, in microcosms and more complex systems, by short-term or low intensity grazing, but reduced when large areas of mycelium were removed by high-intensity grazing. Effects of differential fungal palatability on invertebrate populations are evident in microcosm studies of collembola. These bottom-up effects can be extrapolated more broadly than top-down effects; fungal community dominance determined collembola abundance and diversity, in mesocosms, and woodlouse abundance in the field. Using, as a case study, a series of experiments conducted at a range of scales, mechanisms underlying potential climate change effects on grazing interactions and decomposition are also explored. Biotic effects on decomposer community functioning are heterogeneous, depending on fungal dominance and the density of key macro-invertebrate taxa.  相似文献   

5.
The effect of various organisms on the decompositon of chitin in a gnotobiotic soil system was investigated. Chitin decomposers were isolated from the short grass prairie in Colorado and selected by their ability to use chitin as a source of both C and N. Three bacteria, a fungus, and an actinomycete were grown for 45 days in sterile chitin amended (3 mg g?1 chitin-C) and unamended soil microcosms. Net mineralization of ammonium was greatest in the chitin-ainended microcosms. The greatest increases in N mineralization occurred in chitin-amended microcosms containing the fungus and the actinomycete. A second series of sterile soil microcosms amended with chitin (3 mg g?1 chitin-C) were inoculated with decomposers, a fungus and a bacterium, and a nematode and an amoeba (bacteriophagic grazers) in various combinations. Bacterial and grazer populations, NH4+ CO2 evolution, and residual chitin were measured periodically for 80 days. Bacterial grazing reduced bacterial populations, increased N mineralization, but had no effect on the decomposition of chitin.  相似文献   

6.
《Soil biology & biochemistry》2001,33(12-13):1683-1694
In disinfected forest nursery soils, inoculating Douglas fir (Pseudotsuga menziesii) seedlings with the ectomycorrhizal fungal strain Laccaria bicolor S238N significantly increases tree growth after outplantating. However, the success of the inoculation depends on survival of the fungal inoculum in the soil during the pre-symbiotic life of the fungus. We followed the survival of L. bicolor S238N in autoclaved nursery soil in the glasshouse, and under gnotobiotic conditions in autoclaved or γ-irradiated nursery soil. We also studied the effect of the mycorrhiza helper bacterium Pseudomonas fluorescens BBc6R8, which promotes the Douglas fir-L. bicolor S238N symbiosis, on fungal viability. In the glasshouse, fungal viability was assessed by trapping with Douglas fir seedlings. We showed that the fungus retained its viability in a pre-symbiotic state in the soil at least for 23 weeks, which is much longer than that reported in the literature for other ectomycorrhizal fungi. The bacterium did not significantly modify the survival of the fungus. In the gnotobiotic experiments, ergosterol, a specific fungal membrane component, was used to quantify fungal biomass. Fungal behaviour differed with the disinfection technique used, which modified the chemical characteristics of the initial soil. There was no fungal growth in the autoclaved soil but there was a rapid increase of fungal biomass in the irradiated soil. The effect of the bacterium on fungal biomass also varied with a significant stimulation in the autoclaved soil vs. a significant inhibition in the irradiated soil. Our results show that the beneficial effect of the bacterium on the fungus depends on the condition of the fungus, i.e. the greatest benefit occurs when the fungus is growing under unfavourable conditions.  相似文献   

7.
Summary Nematodes were sampled in untreated, acidified, and limed plots in a Norway spruce (Fexboda) and a Scots pine (Norrliden) stand. At Fexboda, the total number of nematodes was significantly reduced after the acidification. This reduction was probably due to a shock effect, because the samples were taken only 5 months after an application of 200 kg H2SO4 ha-1 to the forest floor. However, the root/fungal-feeding Aphelenchoides was not reduced, probably because it is more tolerant of high acid concentrations than most other nematodes. At Norrliden, where the samples were taken 7 years after the last application of H2SO4, no significant differences were found between the acidified and untreated plots. If the treatment with H2SO4 caused similar effects as at Fexboda, the results indicate a recovery of the nematode populations. Decreased predation from lumbricids rather than a recovery of microfloral populations probably allowed this recovery. No marked effect of lime, spread 2 (Fexboda) and 12 years (Norrliden) before the sampling on the numbers of any of the nematode feeding groups was found. This correlated with almost no change in bacterial biomass after liming, while the active fraction of fungal hyphae was unaffected by liming at Fexboda and reduced by liming at Norrliden. A tendency for decreasing numbers of all nematode feeding groups in the limed plots at Norrliden coincided with increasing numbers of lumbricids.  相似文献   

8.
The effects of inoculation with two AM fungi (M1, Glomus caledonium; M2, Glomus spp. and Acaulospora spp.) and a fungivorous nematode Aphelenchoides sp. on growth and arsenic (As) uptake of Nicotiana tabacum L. were investigated in soils contaminated with a range of As. The reproduction of Aphelenchoides sp. was triggered by the co-inoculation of AM fungi regardless of AM fungal isolates and As levels. Stimulative effects of Aphelenchoides sp. on the development of mycorrhiza, slightly different between two AM fungi, were found particularly at the lowest As level. Irrespective of mycorrhizal inoculi, increasing soil As level decreased plant growth, but increased plant As uptake. Co-inoculation of AM fungi and Aphelenchoides sp. led plants to achieving further growth and greater As accumulation at the lowest As level. Results showed that the interactions between AM fungi and fungivorous nematodes were important in plant As tolerance and phytoextraction at low level As-polluted soil.  相似文献   

9.
Previous results from a long-term grassland trial, located in south-east Ireland indicated conserved (homeostatic) nutrient stoichiometry of the soil microbial biomass despite widely varying soil C:N:P ratios. To determine whether this was associated with a change in microbial community structure, rather than a change in microbial physiology, this study characterized the responses of below-ground microbial and nematode community structure to P fertilization. The trial site maintained a range of P fertilisation rates (0–30 kg P ha−1 yr−1) which had been applied since 1968 and soil samples were collected in spring 2009, autumn 2010 and spring 2011. The microbial biomass demonstrated homeostatic stoichiometry over all sampling occasions, particularly of the C:P ratio, despite a 50-fold difference in soil solution C:P ratio. However, microbial and nematode community structure also varied with P fertilisation, indicating that nutrient ratios are maintained even though there were changes in microbial community structure. P fertilization induced a shift from fungal to bacterial dominated decomposition pathways, as indicated by the proportion of bacterial-feeding to fungal-feeding nematodes and bacterial: fungal phospholipid fatty acids (PLFAs). The altered microbial community structure was considered to result from bottom-up control of nutrient quality and quantity by altered vegetation structure and fertilizer inputs, as well as top-down pressures from the nematode community.  相似文献   

10.
Stable isotope analysis has been used as a powerful tool in food web studies in terrestrial ecosystems. In addition the occurrence and abundance of fatty acids may serve as indicator for feeding strategies of soil animals. Here we combine both approaches and investigate the fatty acid composition, δ13C values of bulk tissues and individual fatty acids in soil organisms. The fungi Chaetomium globosum and Cladosporium cladosporioides were isotopically labelled by fructose derived from either C3 or C4 plants, and the fungal-feeding nematode Aphelenchoides sp. was reared on C. globosum. Fungi and nematodes were used as diet for the Collembolan Protaphorura fimata. The sugar source was fractionated differently by fungal lipid metabolism in a species-specific manner that points to a sensitivity of physiological processing to the non-random distribution of 13C/12C isotopes in the molecule. As a general trend stearic acid (18:0) was depleted in 13C compared to the precursor palmitic acid (16:0), whereas its desaturation to oleic acid (18:1 ω9) favoured the 13C-rich substrate.Fatty acid profiles of P. fimata varied due to food source, indicating incorporation of dietary fatty acids into Collembolan tissue. Individuals feeding on fungi had lower amounts in C20 fatty acids, with monoenoic C20 forms not present. This pattern likely separates primary consumers (fungivores) from predators (nematode feeders). The isotopic discrimination in 13C for bulk Collembola ranged between −2.6 and 1.4‰ and was dependent on fungal species and C3/C4 system, suggesting differences at metabolic branch points and/or isotope discrimination of enzymes. Comparison of δ13C values in individual fatty acids between consumer and diet generally showed depletion (i.e. de novo synthesis) or no changes (i.e. dietary routing), but the fractionation was not uniform and affected by the type of ingested food. Fatty acid carbon isotopes were more variable than those of bulk tissues, likely due to both the distrimination by enzymes and the different lipid origin (i.e. neutral or polar fraction).  相似文献   

11.
Summary The structure of the below-ground detrital food web was similar in three different semiarid vegetation types: lodgepole pine (Pinus contorta subsp. latifolia), mountain meadow (Agropyron smithii), and shortgrass prairie (Bouteloua gracilis). The densities of component food-web functional groups and the response to removal of component groups, differed however. As measured by biomass, bacteria were dominant in the meadow and prairie, while fungi were dominant in the forest. Resourde-base dominance was reflected in consumer dominance, and both directly correlated with the form of inorganic N present. Bacterial-feeding nematodes were numerically dominant in the meadow and prairie, while microarthropods were dominant in the forest. Ammonium-N was the dominant form in the forest, while nitrate —nitrite-N was the more important form in both bacterial-dominated grasslands.Addition of a biocide solution containing carbofuran and dimethoate reduced the numbers of both microarthropods and nematodes. In the bacterial-dominated grasslands, these reductions resulted in no apparent effect on bacterial densities because one group of bacterial consumers (protozoa) increased following the decrease in bacteria-feeding nematodes, in increased fungal biomass, and in increased soil inorganic N. Conversely, in the forest, following the biocide-induced reduction in consumers, the total fungal biomass decreased, but inorganic-N levels increased. The meadow appeared to be the most resilient of the three ecosystems to biocide disturbance, as both nematode and arthropod numbers returned to control levels more rapidly in the meadow than in the prairie or the forest.  相似文献   

12.
Two nematode species (Cruznema tripartitum and Acrobeloides bodenheimeri) were selected to test the hypotheses that bacterial-feeding nematodes affect bacterial biomass and activity and that this feedback effect varies with nematode species and population size. For each species, nematodes of three initial population sizes were inoculated onto bacterial colonies in separate microcosms. Nematode population, bacterial biomass and CO2 production were monitored in parallel microcosm settings. The responses of bacterial biomass to nematode species were different. Bacterial biomass increased significantly on d 8 in the presence of Acrobeloides when its initial numbers were 20 and 100 per microcosm; and bacterial biomass increased significantly on d 4 in the presence of Cruznema when its initial numbers were 5 and 20 per microcosm. Daily CO2 production of the microcosms with initial population sizes of 5, 20 and 100 Cruznema or of 5 and 100 Acrobeloides was significantly greater than that in microcosms without nematodes. However, the CO2 production of the microcosms with initial population of 20 Acrobeloides was not significantly different from that of the microcosms without nematodes. The increase in daily CO2 production per microcosm by Cruznema was generally greater than that by Acrobeloides for the first few days of the experiment. Nevertheless, the increase in daily CO2 production by an individual nematode was similar for both species and was a decreasing function of the initial nematode numbers. The feedback effect of each nematode species on its bacterial prey was estimated by fitting both bacterial biomass and CO2 production data to a model. Model outputs demonstrated that the feedback effect of Cruznema on bacteria was greater than that of Acrobeloides during the course of the experiment and the feedback effect of each species was not linearly correlated to initial nematode population sizes. Cruznema increased bacterial biomass and activity by a factor of 3.75-4.55 over the first 4 d, while Acrobeloides increased it by a factor between 1.97 and 3.40.  相似文献   

13.
The relative importance of litter quality and site heterogeneity on population dynamics of decomposer food webs was investigated in a semi-natural mixed deciduous forest in Denmark. Litterbags containing beech or ash leaves were placed in four plots. Plots were located within gaps and under closed canopies at two topographically different sites, above and below a slope, respectively, to cover variable environmental conditions. Litter was collected after 2, 4 and 9 months of decomposition. Extensive decay prevented analysis of ash after 9 months. Density of bacteria (CFU), active fungal mycelium (FDA), protozoa (MPN) and nematodes were 4-15-fold higher in ash leaves than in beech leaves in accordance with the higher resource quality of ash. Similar effects of site on density of decomposers were evident in both litter types: with some exceptions, decomposers were higher at the low site and stimulated in gaps. Taxonomic diversity of nematodes increased during decomposition and functional diversity of nematodes followed a pattern often encountered, i.e. opportunistic bacterial-feeders were gradually replaced by fungal-feeders and slower growing bacterial-feeders while predators and omnivors peaked at the end of the study period. At the first sampling, where bacterial activity prevailed, the relative abundance of the two dominant bacterial-feeders, Rhabditidae (fast growing) and Plectus spp. (slower growing), depended more on site than litter type. At the second sampling where fungal activity became more important, the proportions of bacterial and fungal-feeding nematodes also depended more on site than on litter type. At the third sampling individual nematode taxa responded differently to site. In summary, we conclude that although litter quality had a major influence on the density of organisms in the decomposer food web, site effects were also detected and nematode functional groups responded more to site than to litter quality early on in the decomposition process.  相似文献   

14.
The effect of increasing nematode abundance on microbial biomass and activity in a temperate grassland soil was investigated in a microcosm experiment. The experiment lasted for 33 days. The natural nematode diversity, as well as relevant aspects of the spatial heterogeneity of the soil microhabitat in a 80 m2 sampling area were maintained in the microcosms. No correlation was found between nematode abundance and microbial biomass (CFE) or ergosterol content (as a measure of active fungal biomass). However, a doubling of nematode abundance reduced CO2 production by 11 % and increased bacterial substrate utilization (BIOLOG) by 18 %. A possible explanation is that fungal activity was strongly reduced at higher nematode density, overcompensating the simultaneous increase in bacterial activity. The results show that the nematode community in a grassland soil is capable of causing a considerable shift in soil microbial activities towards an increased bacterial metabolism, overriding the spatial heterogeneity of the soil habitat and the taxonomic diversity of the community itself, and thereby producing functional effects relevant at spatial scales that far exceed the activity domains of the organisms involved.  相似文献   

15.
Soil nematode communities were investigated at eight semi-natural steppe grasslands in the National Park Seewinkel, eastern Austria. Four sites were moderately grazed by horses, cattle and donkeys, four were ungrazed. Nematodes were sampled on four occasions from mineral soil, and their total abundance, diversity of genera, trophic structure and functional guilds were determined. Altogether 58 nematode genera inhabited the grasslands, with Acrobeloides, Anaplectus, Heterocephalobus, Prismatolaimus, Aphelenchoides, Aphelenchus, Tylenchus and Pratylenchus dominating. Mean total abundance at sites was 185–590 individuals per 100 g soil. Diversity indices did not separate communities well, but cluster analysis showed distinct site effects on nematode generic structure. Within feeding groups the relative proportion of bacterial-feeding nematodes was the highest, followed by the fungal- and plant-feeding group. Omnivores and predators occurred in low abundance. The maturity indices and plant parasite indices were characteristic for temperate grasslands, but the abundance of early colonizers (c-p 1 nematodes) was low. A high density of fungal-feeding c-p 2 families (Aphelenchoidae, Aphelenchoididae) resulted in remarkably high channel index values, suggesting that decomposition pathways are driven by fungi. Nematode community indices of all sites pointed towards a structured, non-enriched soil food web. At most sites, grazing showed little or no effect on nematode community parameters, but total abundance was higher at ungrazed areas. Significant differences in the percentage of omnivorous nematodes, the sum of the maturity index, the number of genera and Simpson's index of diversity were found at one long-term grazed pasture, and this site was also separated by multi-dimensional scaling (MDS).  相似文献   

16.
There are no methods at hand with a long and proven record for assessing the relative contribution of fungi and bacteria to decomposer activity in soil. Whereas a multitude of methods to determine fungal and bacterial biomass are available, activity assays traditionally relied on the substrate-induced respiration (SIR) inhibition approach. Here we compare fungal contribution to the microbial active biomass assessed by the SIR inhibition method with the contribution of fungal-feeding nematodes to the microbial-feeding nematode community. Four cultivation systems on the same soil that differ in carbon inputs with a factor two ranked exactly the same with the two methods. A conventionally farmed rotation with low organic input had the lowest fungal fraction, while three organically farmed soils ranked higher.  相似文献   

17.
Classical and molecular methods were used to study the nematode communities associated with rhizosphere soil and roots of a collection of 16 olive cultivars from a world olive germplasm bank in Mengibar (Jaen province, southern Spain). Classical nematological analysis, including soil nematode extraction, species counting and morphological identification showed that 24 taxa belonging to 9 genera (including Aphelenchoides, Criconemoides, Ditylenchus, Filenchus, Helicotylenchus, Merlinius, Paratylenchus, Tylenchus, and Xiphinema) and 8 families (including Anguinidae, Aphelenchidae, Belonolaimidae, Criconematidae, Hoplolaimidae, Longidoridae, Tylenchidae and Tylenchulidae) of plant-parasitic nematodes were present, with one species (Helicotylenchus digonicus) being prevalent in all samples. The low values of the plant-parasitic nematode index (PPI) indicated a high disturbance of the field soil probably due to application of herbicides and fertilizers. Cluster analysis of population densities of the various nematode species, nematode trophic groups, and ecological indices grouped most olive cultivars into three main clusters indicating that olive genotypes differ in the nematode communities in their rhizosphere soil. The use of T-RFLP analysis discriminated to a higher extent the nematode communities present in the rhizosphere soil from the different olive cultivars as compared to the morphological-based analysis. This study provides the first evidence of an effect of the olive genotype on nematode community composition by combining classical morphological and molecular approaches.  相似文献   

18.
The nematophagous fungi Arthrobotrys oligospora and Myzocytiopsis glutinospora increase to large numbers (>103 propagules/g of soil) when moth larvae killed by entomopathogenic nematodes are added to soil microcosms. In spite of these increases, it is unclear how effective these nematophagous fungi are in suppressing nematodes. We measured nematode mortality in microcosms with small numbers of assay nematodes, and we examined assay nematodes recovered at the end of the experiment for signs of fungal parasites. Because the microcosms did not have a moat or other refuge, the assay nematodes remained vulnerable for the 3 days that they were in the soil. Mortality in this experiment was not substantially increased compared to a previous experiment, which measured the mortality of a larger number of assay nematodes in microcosms surrounded by a moat. Mortality, however, increased from 34 to 50% when recovered assay nematodes were examined and when those with conidia of the nematophagous fungus Hirsutella rhossiliensis were considered dead. The zoosporic fungus M. glutinospora was not detected, perhaps because the soil water potential was too low. Contrary to our expectations, there was no evidence of negative feedback on nematodes (i.e., no evidence of density-dependent mortality) because the addition of dead moth larvae greatly increased numbers of resident nematodes and A. oligospora but did not greatly affect the probability of nematode mortality.  相似文献   

19.
The classification of nematodes in the family Tylenchidae into plant parasites, plant associates or fungal-feeders for community analyses, have been much discussed by nematode ecologists. For an appropriate classification, fungal-feeding habits in the family need to be studied. To evaluate the host status of 10 fungal isolates for Filenchus misellus (Tylenchidae) and Aphelenchus avenae (Aphelenchida, Aphelenchidae), population growth rates, body length and width and sex ratios of the nematodes were measured after 40-day culture on fungal colonies at 25 °C. For F. misellus, the fungi determined as good hosts were two Basidiomycota fungi (Agaricus bisporus, Coprinus cinereus), three Ascomycota fungi (Chaetomium cochlioides, Chaetomium funicola, Chaetomium globosum) and a plant-pathogenic fungus (Rhizoctonia solani) on the basis of nematode population growth rate and female body length. Interestingly Pleurotus ostreatus, known as a predaceous fungus for the other nematodes, was also a good host for F. misellus. While, for A. avenae, good hosts were four plant-pathogenic fungi (Fusarium oxysporum f. sp. conglutinans, F. oxysporum f. sp. cucumerinum, Pythium ultimum, R. solani) and A. bisporus. A. avenae was trapped and preyed upon by Pleurotus hyphae. In F. misellus, males were 7-21% of adults, but the ratio did not correlate significantly with the population growth rate. In A. avenae, no male occurred. Differences in habitat preference between Filenchus and Aphelenchus were explained on the basis of the host status and habitat preferences of the tested fungi.  相似文献   

20.
Fungi are primary agents of organic matter decomposition in forests. Although invertebrate grazing affects fungal biomass and morphology, the species-specific consequences of these interactions are little understood. Using three collembola species (Folsomia candida, Protaphorura armata, Proisotoma minuta) we employed a multi-trophic approach to investigate the individual effects of invertebrate grazing on four species of saprotrophic basidiomycete fungi growing in two species (one fungus: one collembola) soil microcosms. We studied these effects at three trophic levels: the rate of wood decay brought about by the fungi was assessed; fungal growth was characterized across multiple time points using a range of image analysis parameters (radial extension, hyphal coverage, fractal dimension); and collembola abundance was determined at the end of the experiment. Collembola species had different impacts both within and across fungal species; F. candida had the greatest effect on fungal mycelia whereas P. armata often had little impact. Fungal species varied in their resilience to grazing; all collembola species modified Phanerochaete velutina and Hypholoma fasciculare morphology, that of Resinicium bicolor was only markedly affected by F. candida, and effects on Phallus impudicus were negligible. In the case of H. fasciculare, these grazing effects translated into effects on the rate of fungus-induced wood decay: F. candida and P. armata, but not P. minuta, reduced wood decay rate compared to ungrazed controls. Rate of wood decay was unaffected in the other three fungal species. Changes in collembola population size were generally consistent across fungal species, with each species achieving a greater abundance on P. velutina than on H. fasciculare and P. impudicus. The collembola species did, however, respond differently to R. bicolor, with F. candida being more successful than P. armata. Our study suggests that a wide range of impacts can occur during fungus–collembola interactions, and that caution should be exercised when treating saprotrophic fungi and mycophagous collembola as uniform functional components.  相似文献   

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