Non‐trophic effects of oribatid mites on cord‐forming basidiomycetes in soil microcosms

1. Saprotrophic cord‐forming basidiomycetes are the primary agents of decomposition in forest ecosystems. Collembola and oribatid mites affect fungal growth and foraging, and therefore decomposition, through direct mycelial grazing. 2. Grazing on the fungal species Hypholoma fasciculare, Resinicium bicolor and Phanerochaete velutina by the collembola Folsomia candida, and the oribatid mites Steganacarus magnus, Euzetes globulus and Hermannia gibba was investigated in soil microcosms. 3. Folsomia candida grazed on all fungal species: radial extent of R. bicolor, hyphal coverage of all fungal species, and fractal dimension of R. bicolor and P. velutina were all reduced. Oribatid mites did not graze the fungi but did affect mycelial morphology. Steganacarus magnus caused a reduction in the radial extent of H. fasciculare, and the hyphal coverage and fractal dimension in both H. fasciculare and R. bicolor. Euzetes globulus and H. gibba reduced the hyphal coverage of P. velutina. 4. Oribatid mites are associated with a cornucopia of chemical secretions with possible anti‐fungal properties. Chemical analysis of H. gibba opisthonotal secretions revealed four main compounds, all of which are new to the known spectrum of opisthonotal components. The most abundant was (E)‐β‐farnesene. 5. Treatment effects were species‐specific in terms of both fungal and invertebrate species. This study provides the first evidence of non‐grazing effects of oribatid mites on fungal growth and morphology. This could potentially influence the spatial organisation of mycelium in forest soils and therefore the ability of fungi to locate, colonise and decompose dead organic matter.     

Reorganization of mycelial networks of Phanerochaete velutina in response to new woody resources and collembola (Folsomia candida) grazing

Mycelial development of Phanerochaete velutina extending from wood inocula in 57 × 57 cm trays of non-sterile soil was characterized after adding: (1) collembola; (2) new wood resources; (3) both new wood resources and collembola; and (4) no new resources and no collembola. After 99 d, all systems had produced distinct mycelial cords, much of the diffuse mycelium and thinner cords that were produced early on having regressed. Systems to which new resources (but no collembola) had been added developed thick cords interconnecting inocula with new resources, and much of the non-connected mycelium regressed. Nonetheless, these systems had significantly greater hyphal coverage and mass fractal dimension than the other treatments, resulting from outgrowth from the new resources. Unexpectedly, morphology of grazed systems with no added resources was very similar to that of ungrazed systems with no added resources, apparently because the collembola grazed on senescing hyphae that would ultimately have regressed. Where new resources and collembola were added, there was proliferation of fine mycelium along connective cords and elsewhere, but this was not as extensive as in the new resource/no collembola systems, the fine mycelium apparently being grazed in patches. Fungus gnat (family Sciaridae) larvae contaminated eight (out of 14) trays with no added collembola, but none of the systems to which collembola had been added. They burrowed around the wood and caused cords to be severed.     

Effect of soil and litter type on outgrowth patterns of mycelial systems of Phanerochaete velutina

Abstract: The outgrowth patterns of Phanerochaete velutina from woody resources varied depending on the soil/litter type. There were clear differences in mycelial extension rate, time between contact with and emergence from baits, mycelial biomass, and extra-resource mycelial responses to contact with new resources depending on soil type, though there was little difference between fractal dimension, i.e. space filling, of mycelia with time or soil/litter type. In a few replicates, particularly in components from the Lawson's cypress stand, mycelia sometimes became brownish colour, ceased growth and eventually disintegrated. In litter the pattern of mycelial development was quite different from that in soil due to subsurface growth in which needles were often colonised. In humus, mycelial development was somewhat similar to that in soil.     

Production and effects of volatile organic compounds during interspecific interactions

Competition between mycelia of saprotrophic cord-forming basidiomycetes occurs both within dead woody resources and in the soil-litter interface, and involves a variety of antagonistic mechanisms including the production of volatile organic compounds (VOCs). The antagonistic potential of VOC profiles from interactions in wood blocks and in soil microcosms was assessed using shared headspace experiments, and the profile of VOCs emitted over the course of interactions elucidated using solid phase microextraction (SPME) with gas chromatography-mass spectrometry (GC–MS). Quantitative and qualitative changes in VOC production occurred in interactions compared to self-pairing controls, with different VOC profiles from fungi growing in wood blocks compared to soil trays. There were both stimulatory and inhibitory effects of VOCs on target mycelial extension rate, hyphal coverage and fractal dimension. VOC-mediated effects were greater in self-pairing controls compared to interactions, and differed depending on the substratum in which the VOC-producing fungi were growing.     

Heavy metals have different effects on mycelial morphology of Achlya bisexualis as determined by fractal geometry

The morphological response, as measured by changes to mycelial area, radial extension and border fractal dimension, of the oomycete Achlya bisexualis to Cu, Co, Hg, Zn and Cd at concentrations of between 0.05 and 3 mM is described. All of the metals decreased mycelial area and radial extension. Border fractal dimension increased in the presence of Cu, Co and Hg with individual hyphae extending out beyond the mycelial margin. In the presence of 3 mM Hg these hyphae displayed spiral growth. Zn and Cd had no effect on border fractal dimension. We suggest that all of the metals slow growth and that Cu, Co and Hg may also disrupt the relationship between tip growth and branching at the edge of the mycelium.     

Relationships between phosphatidylcholine content, chitin synthesis, growth, and morphology of Aspergillus nidulans choC

The phosphatidylcholine (PC) content of Aspergillus nidulans choC was varied by growing the auxotroph in medium containing various concentrations of choline chloride. Direct linear correlations were observed between PC content and in vivo chitin synthase activity, between in vivo chitin synthase activity and mean hyphal extension rate, and between mean hyphal extension rate and hyphal growth unit length; hyphal growth unit length is a measure of hyphal branching. Further, there was a correlation between PC content and colony radial growth rate. Thus, membrane composition is an important determinant of both hyphal (and colony) extension rate and mycelial morphology.     

Encounter with New Resources Causes Polarized Growth of the Cord-Forming Basidiomycete Phanerochaete velutina on Soil

Abstract The development and physiology of cord-forming saprotrophic basidiomycetes, which form extensive and persistent mycelial networks in woodland ecosystems, can be conveniently studied on non-sterile soil in laboratory microcosms mimicking field conditions. Morphological responses of Phanerochaete velutina mycelial systems to resource encounters, and decay partitioning following encounters, varied according to whether simulated woody litter was unsterile or autoclaved and on whether encounter took place at the mycelial foraging front or behind the margin (simulating litter fall onto established systems in the field). Results show that encounter of discrete resources by P. velutina is rapidly communicated to the entire mycelial system; that resource capture takes high priority at the expense of continued system extension and decay-derived carbon reallocation; and that polarized growth toward newly encountered resources, previously considered to occur infrequently with this species, may be readily detected using image analysis techniques. Potential advantages of polarized development of P. velutina are discussed.     

Oxalate and ferricrocin exudation by the extramatrical mycelium of an ectomycorrhizal fungus in symbiosis with Pinus sylvestris

Accurate estimates of mycelial exudation in time and space are crucial for the assessment of ectomycorrhizal involvement in biogeochemical processes. Knowledge of exudation from mycelia of ectomycorrhizal fungi is still limited, especially for fungi in symbiosis with a host. Pinus sylvestris seedlings colonized by Hebeloma crustuliniforme were grown in aseptic multicompartment dishes. This novel system enabled identification of exudates originating only from extramatrical mycelium. At harvest, hyphal density and numbers were estimated using microscopic imaging. A fractal geometric approach was adopted for calculation of exudation rates. The main compounds identified were oxalate and ferricrocin. The exudation rate for oxalate was 19 +/- 3 fmol per hyphal tip h(-1) (mean +/- standard error of the mean) or 488 +/- 95 fmol hyphal mm(-2) h(-1). Ferricrocin rates were approx. 10 000 times lower. The fractal dimension (D) of the mycelia was 1.4 +/- 0.1, suggesting an explorative growth. Potassium nutrition was a significant regulatory factor for ferricrocin but not oxalate. The results suggest that hyphal exudation may alter the chemical conditions of soil microsites and affect mineral dissolution. Calculations also indicated that oxalate exudation may be a significant carbon sink.     

Grazing by Folsomia candida (Collembola) differentially affects mycelial morphology of the cord-forming basidiomycetes Hypholoma fasciculare, Phanerochaete velutina and Resinicium bicolor

Cord-forming basidiomycetes are important decomposers of dead wood in forest ecosystems but the impact of mycophagous soil invertebrates on their mycelia are little known. Here we investigate the effects of different grazing intensities of Collembola (Folsomia candida) on mycelial foraging patterns of the saprotrophic cord-forming basidiomycetes Hypholoma fasciculare, Phanerochaete velutina and Resinicium bicolor growing from beech (Fagus sylvatica) wood block inocula in dishes of non-sterile soil. Mycelial extension rate and hyphal coverage decreased with increased grazing intensity. R. bicolor was most affected, high grazing density resulting in only a few major cords remaining. Grazing of H. fasciculare often resulted in points of more rapid outgrowth as cords with a fanned margin. In grazed mycelia of P. velutina the main cords had fanned tips and lateral cords became branched. These results suggest that mycophagy by Collembola may hinder the growth of cord-forming fungi in woodlands, which might impact on the ability of these fungi to forage for and decompose dead organic material.     

Impacts of grazing soil fauna on decomposer fungi are species-specific and density-dependent

The grazing impacts of different densities of woodlice, collembola and millipedes on the foraging and distribution of two saprotrophic cord-forming basidiomycetes were investigated in soil microcosms. Effects of all three invertebrate species were density-dependent, with larger populations limiting mycelial development to a greater extent. Impacts were, however, species-specific; grazing pressures exerted by low-density woodlouse populations outweighed those of high-density millipede or collembola populations. The varying abilities of soil invertebrates to influence mycelial foraging and distribution indicate that invertebrate species composition and diversity may be key factors regulating saprotrophic basidiomycete functioning in woodland soil.     

Effects of belowground grazing by collembola on growth,mycorrhizal infection,and P uptake of Geranium robertianum

We hypothesized that the grazing of vesicular-arbuscular mycorrhizal (VAM) hyphae by soil animals could be responsible for the lack of a direct relationship between mycorrhizal infection intensity and nutrient uptake under field conditions. To test this hypothesis, we determined the effect of a range of densities of the collembola, Folsomia candida, on growth, VAM infection, and P uptake in Geranium robertianum, a common forest herb, under greenhouse conditions. Total and aboveground growth were greater at low collembola density than either at higher collembola density or without collembola. These differences were greater when the plants were grown in a high organic content soil mix than when grown in sand. Root mass was not affected by collembola density. In the soil mix, root length decreased with increasing collembola density, but not in the sand. The percent of root length infected with VAM was lower at any collembola density than when collembola were absent. Total infected root length decreased linearly with increasing collembola density. Few significant differences in P uptake or tissue concentration were found. Thus, plant growth (but not P uptake) may be stimulated at low collembola density and inhibited at high. We discuss mechanisms which may be responsible for this non-linear response, and the implications of the pattern of response to studies of plant competition, nutrient turnover, and revegetation.     

Impacts of elevated temperature on the growth and functioning of decomposer fungi are influenced by grazing collembola

Elevated temperature has potential to influence the biological mechanisms regulating ecosystem–atmosphere carbon exchange. The relationship between warming and heterotrophic microbial respiration remains poorly understood, not least in terms of the differential sensitivity of microbial groups to temperature and the complexity of interactions with other biota. Cord‐forming basidiomycete fungi are dominant primary decomposers in temperate woodland. Decomposition rates are determined by the composition of the decomposer community, ecophysiological relationships between these fungi and abiotic variables and interactions with other organisms. Amongst the latter, a major determinant is the balance between mycelial growth and removal by soil invertebrate grazers, which can themselves be affected by elevated temperature. We investigated the impact of elevated temperature on fungal foraging and decomposition of beech (Fagus sylvatica) wood in soil microcosms to which the invertebrate grazers, Folsomia candida and Protophorura armata (Collembola), were added in factorial combinations with five basidiomycete fungi. Species‐specific impacts on mycelial development and function resulted from differential sensitivity of fungi to warming and grazing. Temperature impacts on collembola abundance were resource‐specific, causing increased grazing pressure by both species, but on different fungi. Grazing often counteracted warming‐induced stimulation of mycelial growth, but occasionally amplified the temperature effect, with implications for colonization rates of new resources. High grazing pressure did not prevent increased fungal‐mediated decomposition of colonized wood, as fungi utilized more resource‐derived energy to maintain explorative growth. Impacts of elevated temperature on decomposition are likely to depend on local composition of the fungal and invertebrate decomposer community.     

Effects of temperature, pH, water activity and CO2 concentration on growth of Rhizopus oligosporus NRRL 2710

AIMS: To investigate the effects of temperature, pH, water activity (aw) and CO2 concentration on the growth of Rhizopus oligosporus NRRL 2710. METHODS AND RESULTS: Hyphal extension rates from mycelial and spore inocula were measured on media with different aw (approximately 1.0, 0.98 and 0.96) and pH (3.5, 5.5 and 7.5) incubated at 30, 37 or 42 degrees C in atmospheres containing 0.03, 12.5 or 25% (v/v) CO2. The effects of environmental conditions on hyphal extension rate were modelled using surface response methodology. The rate of hyphal extension was very sensitive to pH, exhibiting a pronounced optimum at pH 5.5-5.8. The hyphal extension rate was less sensitive to temperature, aw or CO2, exhibiting maximum rates at 42 degrees C, a(w) approximately 1.0 and 0.03% (v/v) CO2. CONCLUSIONS: The fastest hyphal extension rate (1.7 mm h(-1)) was predicted to occur at 42 degrees C, pH 5.85, a(w) approximately 1.0 and 0.03% CO2. SIGNIFICANCE AND IMPACT OF THE STUDY: The present work is the first to model the simultaneous effects of temperature, pH, aw and CO2 concentration on mould growth. The information relates to tempe fermentation and to possible control of the microflora in Tanzanian cassava heap fermentations.     

轮牧方式对荒漠草原土壤团聚体及有机碳特征的影响

合理的草地轮牧方式对草原的科学管理具有重要意义.以宁夏荒漠草原为研究对象,对围封禁牧、连续放牧和二区、四区及六区轮牧下0~30 cm土层土壤团聚体分布特征、稳定性、有机碳含量及其贡献率进行了研究.结果表明: 除围封禁牧草地以机械稳定性大团聚体为主外,其他处理的土壤水稳性团聚体均以微团聚体为主;增加轮牧分区有利于表层土壤水稳性团聚体含量的保持及大团聚体含量增加.机械稳定性团聚体分形维数在连续放牧下最大,增加轮牧分区则呈现减小趋势,但水稳性团聚体分形维数无明显变化规律;团聚体平均重量直径(MWD)及几何平均直径(GMD)在禁牧草地最大,且随着轮牧分区的增加而增大;MWD和GMD与微团聚体含量呈显著负相关.水稳定性大团聚体有机碳含量以六区轮牧和围封禁牧较高,二区轮牧和连续放牧较低;试验区微团聚体有机碳对土壤有机碳含量贡献率较高,但0~20 cm土层中,轮牧分区越多则大团聚体有机碳贡献率越高.从土壤团聚体及其有机碳特征考虑,六区轮牧为研究区荒漠草原最适宜的轮牧方式.     

松嫩草原中度退化草地不同植被恢复方式下土壤跳虫群落特征比较

依据 2005 年 5－10 月在松嫩草原中度退化草地不同植被恢复处理条件下采集的土壤跳虫群落数据,应用类群数、个体密度和多样性指数等多个群落参数,研究了不同植被恢复方式下松嫩草原中度退化草地土壤跳虫群落特征的差异。本研究共捕获跳虫 1 156只,隶属于 9 科 19 属。结果显示：与过度放牧相比,围栏封育和种植苜蓿都能改善土壤理化性质,且拥有较高的跳虫类群数、个体密度和群落多样性。围栏封育和种植苜蓿都能达到恢复与重建中度退化草地土壤跳虫群落的目的, 只是与围栏封育相比,种植苜蓿能够更显著地提高跳虫个体密度。此外,与过度放牧相比,围栏封育和种植苜蓿主要提高了跳虫群落等节跳虫科（Isotomidae）、长角跳虫科（ Entomobryidae）和圆跳虫科（Sminthuridae）个体密度和类群数,其中围栏封育样地拥有更高的长角跳虫科和圆跳虫科个体密度,其分别是过度放牧样地相应跳虫科的 5.14倍和 2.38倍;而种植苜蓿样地等节跳虫科个体密度最大,其大小是过度放牧样地等节跳虫科的 3.33倍。     

Evidence for the independent regulation of hyphal extension and branch initiation in Fusarium graminearum A3 5

Abstract Addition of 100 μM choline chloride to the medium increased (by approx. 36%) both the length of the hyphal growth unit ( G a measure of mycelial branching) and the mean hyphal extension rate ( E ) of Fusarium graminearum but did not increase the maximum rate of extension of the hyphae ( E _max). The paramorphogen, edifenphos (Hinosan) reduced G and E without affecting specific growth rate (μ). However, when mycelia were treated with edifenphos plus choline, μ was reduced, G was increased by approx. 35%, but E and E _max were not affected. The results suggest that the primary effect of edifenphos is inhibition of hyphal extension, whilst the primary effect of choline is inhibition of branch initiation.     

Effects of collembola (arthropoda) and relative germination date on competition between mycorrhizalPanicum virgatum (Poaceae) and non-mycorrhizalBrassica nigra (Brassicaceae)

In this experiment the separate and interactive effects of grazing of vesicular-arbuscular mycorrhizal hyphae by collembola and of relative germination date on competition between the mycorrhizal perennial grassPanicum virgatum and the non-mycorrhizal annual cruciferBrassica nigra were investigated. In the absence of competition,P. virgatum mass and P uptake were not affected by collembola grazing; grazing did reduce tissue N concentration and root: shoot ratio. Competition fromB. nigra plants of the same age/size (“simultaneous competition”) significantly reducedP. virgatum total, root, and shoot mass relative to control plants not subject to competition. In contrast, when in competition,B. nigra plants did not differ in biomass fromB. nigra controls grown without competition. Simultaneous competition also reduced N and P uptake byP. virgatum, but not byB. nigra. Grazing by collembola during simultaneous competition increased the differences in nutrient uptake and tended to shift the competitive balance further toward the non-mycorrhizalB. nigra. WhenP. virgatum plants were subjected to competition fromB. nigra plants which germinated three weeks later (“offset competition”) the situation was reversed: offsetB. nigra plants were negatively affected by competition while the larger, olderP. virgatum plants were not. Thus, relative germination date is important in determining the relative competitive ability of these two species. Grazing by collembola did not affect offset competition. The grazing of VAM hyphae by collembola appears to increase N availability in this experimental system. Under simultaneous competition, this N is taken up by the more extensive root system ofB. nigra; under offset conditions, the root system of the smallerB. nigra plants is insufficient to take advantage of the added resources. Thus, we suggest that grazing-induced transient changes in nutrient availability and the differential abilities of the two species to make use of these added resources constitute the mechanisms by which relative germination date and collembola grazing influence competition.     

The effect of domestic sheep on forage plants of wild reindeer; a landscape scale experiment

Domestic herbivores often compete with wildlife for limited resources, and on longer time-scales, grazing may also increase or decrease coverage of important food plants to wildlife affecting the threshold density for when competition can be expected. In Norway, there are growing concerns about the effect of releasing 2.1 million domestic sheep (Ovis aries) for summer grazing into areas hosting wild populations of alpine reindeer (Rangifer tarandus). We quantified the effect of sheep grazing (0, 25 and 80 sheep/km²) on the development in coverage and abundance of plants known to be important in the diet of reindeer during summer (vascular plants) and winter (lichens) within a fully replicated, landscape scale (2.7 km²) experiment. From 2001 to 2005, the sedge, Carex bigelowii, increased while the herb Solidago virgaurea decreased in frequency at high density of sheep relative to controls (both marginally non-significant). There was no marked development in Deschampsia flexuosa, Salix herbacea or Hierarcium alpinum that could be related to sheep grazing intensity. Lichen coverage and height both decreased at high density of sheep from 2002 to 2005. Effects of low grazing intensity were closer to controls than to high grazing intensity. Our study highlights that high sheep grazing intensity induce changes to the plant community that, at the same time, can improve the summer habitat and detriment the winter habitat to reindeer. Many wild reindeer populations are fragmented and may thus be limited by either summer or winter range. The effect of sheep grazing is predicted to vary accordingly. However, currently, we have limited ability to quantify how much this explicitly means in terms of increased or reduced carrying capacity for reindeer.     

Morphological measurements on Penicillium chrysogenum broths by rheology and filtration methods

The morphology parameters of mycelial culture (Penicillium chrysogenum) were measured and quantified by rheology and filtration methods. Two of the morphology parameters obtained from rheology measurements, delta defined by the Casson equation and delta* defined by intrinsic viscosity, were found to vary systematically with broth age and with the observed morphology by microscopy. Three of the filtration parameters, hyphal density, Kozeny constant, and index of compressibility, are demonstrated as sensitive indicators of the broth age and mycelial morphology. Two of the morphology parameters, delta and delta*, were used to cross-correlate with hyphal density. Because various mycelial fermentations require different growth morphologies (pellet and filament) for optimum product yield and the morphology of mycelial broths varies with broth age, it is suggested that these morphology parameters could be used to represent the morphology of mycelial broths quantitatively. (c) 1993 John Wiley & Sons, Inc.