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Non-destructive quantification of growth and regression of mycelial cords using image analysis
... ting assessment of mycelial development. In these model systems, qualitative (Dowson, Rayner & Boddy, 1986;Dowson et al., 1989) and quantitative studies Bolton, Morris & Boddy, 1991;Bolton & Boddy, 1993) showed that, typically, foraging mycelium which encounters and colonizes a new resource unit thickens to form persistent cords at the expense of mycelium which fails to locate potential carbon sources, which might regress. These effects, and the timescale over which they might occur, are dependent, however, upon species and the quantity and quality of resource units available within cord systems. ...
... These effects, and the timescale over which they might occur, are dependent, however, upon species and the quantity and quality of resource units available within cord systems. Rapid and non-destructive quantitative assessment of changes in cord system development is now possible using image analysis of model cord systems (Bolton et al., 1991;Donnelly, Wilkms & Boddy, 1995). Objective descriptors of foraging behaviour can now be derived from the application of fractal geometry techniques to captured images (Donnelly et al., 1995;Abdalla & Boddy, 1996;Donnelly & Boddy, 1997). ...
... The de\'elopmental polarity seen here, when wood baits were supplied, contrasts markedly with previous studies on this species. Re-allocation of mycelial effort from unsuccessful to successful foraging paths on undiluted soil tends to occur only when newly encountered wood resources are larger (for example, a bait to inoculum \-olume ratio of 16; 1) than the existing resources colonized by the mycelial system (Dowson et al., 1986(Dowson et al., , 1989Bolton et al., 1991;Bolton, 1993;Bolton & Boddy, 1993;Hughes & Boddy, 1996). On 'dilute' soil, however, P. velutina systems supplied with a «'ood bait of equal volume to the inoculum displayed regression of mycelium in the unbaited sector of the plate, with a concurrent increase in hyphal co\ er in the woodbaited sector. ...
Development of mycelial cord systems of Phanerochaete velutina (DC.: Pers.) Parmasto from 4-cm3 inocula on a nutrient-depleted non-sterile soil was studied in laboratory microcosms using image analysis techniques. Cord systems were “baited” after 13d growth with either fresh, non-sterile 4-cm3 wood baits or control Perspex® blocks of the same contact area placed behind the foraging mycelial front. After 26 d growth, mycelial ‘patches’ arose by dedifferentiation of consolidated mycelial cords in both wood- and Perspex-baited cord systems. ‘Patches’ comprised fine, highly branched separate hyphae extending radially from points of aggregated hyphae in cords. ‘Patches’ and cords could be readily distinguished by image analysis and the areas covered by patches and cords could be measured and compared. Whilst the total hyphal cover of Perspex- and wood-baited systems did not differ significantly (P > 0.05), patch cover in wood-baited systems was up to 10 times greater than in Perspex-baited systems. Patches were temporary structures, regressing more rapidly with age than mycelial cords. Patch development ceased after application of a nutrient solution which replenished phosphate levels in the soil. Wood-baited mycelial systems displayed significant developmental polarity (P≤ 005) of both total hyphal cover (patches plus cords) and hyphae in patches towards the ‘baited’ sector of cord systems after 42 d, which corresponded with peak patch development. However, significant (P≤ 0.05) developmental polarity of the mycelial systems along the bait-inoculum line could be detected 8 d before patch formation when assessed by fractal geometry. Radiotracer studies showed that mycelial patches were not sinks for supplied 32P, but that they were sites of increased nutrient uptake capacity compared with that of mycelial cords. We discuss the need for mycelial cord systems to balance allocation of mycelial biomass between the two essential processes of colonizing wood resource units, and the acquisition of soluble inorganic nutrients from soil.
... The maximum size of the FMU is thus the whole GMU. It has been shown that large FMUs have a better capacity to spread in an environment and to compete with other fungal species (Dowson, Rayner & Boddy, 1988;Bolton, Morris & Boddy, 1991;Holmer & Stenlid, 1993). This behaviour resembles a feudal state where warlords, tied to each other by intermarriage and each with their own stronghold, join forces into one organized army to attack and conquer other strongholds (and thus resources) held by other states. ...
Fungi are amongst the simplest of eukaryotes. Their study has provided useful paradigms for processes that are fundamental to the way in which higher cells grow, divide, establish form and shape, and communicate with one another. The majority of work has been carried out on the budding yeast Saccharomyces cerevisiae, but in nature unicellular fungi are greatly outnumbered by filamentous forms for which our knowledge is much less well developed. This volume focuses on the analysis of the filamentous life style, particularly on the hyphae which constitute the fungal mycelial colony. It provides the most recent insights into the molecular genetics and physiological mechanisms underlying the elaboration of the branching mycelium and the interactions between individual fungal mycelia. As such it offers much to interest mycologists and, equally, those working in the fields of cell biology, developmental biology, physiology and biochemistry.
... When new resources are encountered the mycelium responds with dramatic changes in morphology (system architecture) and often with considerable reallocation of biomass. When the new resources are substantially larger than those from which the mycelium emanated, mycelium connecting the new resource with the original resource usually aggregates to form thick cords, while radial extension slows or ceases, and non-resource-connected mycelium regresses (Dowson et al., 1986(Dowson et al., , 1988Bolton et al., 1991;Boddy, 1993Boddy, , 1999Bolton, 1993;Donnelly and Boddy, 1997a;Figure 3a-c). Subsequently mycelium grows out from the newly colonized resource, and foraging continues, though the amount of time before foraging continues depends on the sizes of the original and new resource (Bolton, 1993;Boddy and Jones, 2006). ...
To survive saprotrophic fungi must be able to capture organic resources discontinuously dispersed in space and time. Some basidiomycetes can only achieve this by production of sexual and asexual spores or sclerotia — categorized as ‘resource-unit-restricted’, whereas ‘non-resource-unit-restricted’ basidiomycetes can also spread between organic resources as mycelium. Mycelial distribution and foraging within organic resources and among relatively homogeneously and heterogeneously distributed resources is reviewed. ‘Non-resource-unit-restricted’ Basidiomycota have evolved different patterns of mycelial spread appropriate to discovery of resources of different sizes and distributions. They show remarkable patterns of reallocation of biomass and mineral nutrients on discovery and colonization of new resources. Network architecture is a significant factor in the acquisition and distribution of nutrients, and in survival when parts of the network are destroyed. The costs and benefits of different architectures to large mycelial networks are considered.
... Several cord-forming fungi have been shown, in the laboratory, to exhibit remarkable patterns of reallocation of extra-resource mycelial biomass (Dowson, Rayner & Boddy, 1986, 1988Dowson etal., 1989a;Bolton, Morris & Boddy, 1991;Bolton & Boddy, 1993) and nutrients , 1995aWells, Boddy & Evans, 1995;Wells, Hughes & Boddy, 1990) when fresh resources have been encountered by foraging mycelia extending from wood block inocula into non-sterile soil. The rate, extent and timing of re-allocation varies. ...
summaryThe effect of sequential encounter with wood resources (1 cm3 and 2 cm3‘baits’ in various combinations) by mycelial cords of Phanerochaete velutina (DC.: Pers.) Parmasto growing from 1 cm3 wood inocula was investigated in model soil systems in the laboratory. Encountering large wood baits (8 cm3), either next to the inoculum or after encounter of another bait, resulted in cessation of mycelial extension and regression of mycelium from the inoculum and small baits. Small wood baits had no effect on mycelial extension rates, even when encountered in rapid succession. All systems maintained a general polarity when growing out from a bait, but later often curved around the bait, extending over soil which had previously been explored. Allocation of 32P (taken up by the inoculum) between the three resource units (inoculum and two sequentially encountered baits) was investigated; significantly (P≤ 0.05) more 32P was allocated to the large wood baits (whether encountered first or second) than to the other bait; but the inoculum was usually allocated most. Wood inocula decayed more rapidly than baits. The significance of the results is discussed in relation to foraging.
... Studies of the tative evidence that, on cotitact with a new resource dry rot futigus Se)-/)u/a/(7(T/(»(JHs(Wulf.: Fr.) Scbrot. (bait), cord systems reallocate fungal biomass to (Watkinson, 1971;Brownlee & Jentiitigs, 1981, contiecti\e mycelium whilst noti-connective my-1982a, 6; Thompson et al., 1986) and of several celium regresses (Dowson e^ «/., 1986(Dowson e^ «/., , 1988(Dowson e^ «/., /), 1989 naturally-occurring cord-formers (Clipson, Cairney has beeti cotifirmed quatititatively in laboratory 6 Jennings, 1987;Wells Si Boddy, 1990; studies Bolton, Wells, Hughes & Boddy, 1990) have shown that Morris & Boddy, 1991;Bolton & Boddy, 1993). mycelial cords are the main pathway for tiutrient and Studies of phosphorus acquisition by cordwater tratislocation. ...
Movement of radiotracer was monitored in mycelial cord systems developed from wood block inocula, pre-colonized by Phanerochaete velutina (DC: Pers.) Parmasto grown on unsterile soil. In short-term studies, reproducible but low-level loading of radiotracer was observed which was independent of the extent of cord systems. Carbon translocation velocities ranged from 132 to 336 cm h-1, whilst fluxes were estimated to range from 35 to 66 nmol cm-2 h-1 (as glucose). When cord systems were supplied with a range of potential carbon resources as baits considerable movement of carbon was detected over 9 wk. More than 80 % of exogenously supplied carbon was retained in resource units rather than being allocated to extra-resource mycelium. The direction and extent of carbon movement, and partitioning of decay between inocula and baits within cord systems, was dependent upon the type and size of bait and whether or not combinations of baits included wood pre-colonized by other sapro trophic fungi. There was evidence for coordinated use of resources within cord systems and that carbon movement was not a function of mycelial growth. Respiratory carbon losses were greatest when baits included sterile leaf litter packs and least when sterile wood baits were supplied. The results are discussed in terms of nutrient conservation and cycling in cord systems.
... Quantification by automated image analysis is less prone to subjectivity and needs less labor per sample than manual quantification. It has been used to quantify fungal hyphae growing in batch cultures (26), on the soil (3), and in the soil (15). A major disadvantage of automated image analysis is the need for high-quality images. ...
An optical method to quantify the fungal hyphae within decomposing leaves of deciduous trees was developed. The plant matrix was partially destroyed under hydrolytic conditions, and fungal hyphae and cellulose residues within the leaves were stained with Calcofluor M2R. Cellulose residues were subsequently depolymerized by cellulase, and fungal hyphae were separated from the remaining plant matrix with a pressurized air-water mixture. An image analysis program to quantify the fungal hyphae was written. The program included the recognition of fungal hyphae, the elimination of stomata from the images, and the measuring of lengths of fungal hyphae. The optical method was verified by a chemical method relying on glucosamine as an indicator of fungal biomass. The fungal biomass in leaves of Fagus silvatica and Quercus petraea at early states of decomposition was 0.2 to 0.4% of the leaf weight. The biomass reached a maximum within 2 to 4 weeks (optical method, 0.5 to 0.7%; chemical method, 1 to 1.4% of the initial leaf weight) and decreased thereafter.
Terrestrial fungi are commonly studied in the laboratory, growing on artificial media in which nutrients are typically homogeneously distributed and supplied in superabundance, the environment is sterile and microclimate (temperature, moisture, gaseous regime) usually relatively constant. This contrasts with the natural environment, in which: nutrients are often patchily and sparsely distributed or not readily available, because they are locked in recalcitrant material (e.g. lignin); many other organisms are encountered, including other fungi, bacteria and invertebrates; and microclimate is constantly changing, both temporally and spatially. This chapter explores the ways in which fungi cope with environmental heterogeneity. Similar situations are faced by macroorganisms and analogies are drawn. Emphasis is placed on basidiomycetes, not only because they have been studied in most detail, but because of their dominant role as decomposers and mutualistic symbionts (Boddy & Watkinson, 1995; Smith & Read, 1997) and because they are better adapted to respond to environmental heterogeneity over scales ranging from micrometres to many metres than are other fungi. Both saprotrophic and ectomycorrhizal Basidiomycota form extensive mycelial systems in woodland soil and litter, but it is the former that are the focus of this review. Saprotrophic, cord-forming Basidiomycota that ramify at the soil–litter interface, interconnecting disparate litter components, provide most examples. The key feature of these fungi that fits them for growth in environments where resources are heterogeneously distributed is that they are non-resource-unit restricted, i.e. they can grow out of one resource in search of others. © Cambridge University Press 2007 and Cambridge University Press, 2009.
Many saprotrophic fungi, especially basidiomycetes, which are able to grow out of the substratum that they are colonizing in search of new resources (i.e., nonresource-unit-restricted fungi) form mycelial cords, which are aggregations of predominantly parallel, longitudinally aligned hyphae. These cords often form extensive, long-lived systems which interconnect discrete nutrient resources, e.g. woody litter components, on the floor of boreal, temperate and tropical forests, and some can form networks in tropical canopies. They exhibit foraging strategies which vary among species, and which alter depending on resource quantity and quality, the presence of other organisms, and microclimatic environment. The morphological patterns they form are well described by fractal geometry. Their mycelia show remarkable patterns of reallocation of biomass and mineral nutrients when new resources are encountered during mycelial foraging or when new resources are added to mature systems. Mycelial-cord systems encountering heterogeneously distributed organic substrata coordinate use of available resources so that demands are met by 'spreading the load' through the system. The persistent networks, ability to forage for new resources, and ability to reallocate mycelial biomass and nutrients exhibited by saprotrophic cord-forming fungi provide a solution to the problems of life in a spatially and temporally heterogenous environment. Response to the heterogenous environment in which these fungi exist generates heterogeneity in themselves, and they in turn generate heterogeneity in their environment, both in space and time.
Saprotrophic mycelial-cord-forming basidiomycetes, which extend between organic substrata on the forest floor, exhibit remarkable patterns of reallocation of biomass and nutrients when encountering new resources. These have been equated with foraging strategies, and differ between species, resources quality and quantity. Stropharia caerulea occupies more disturbed sites than the fungi previously examined, and the responses of its mycelial foraging systems were investigated non-destructively by image analysis. Resource quantity and quality affected extension rate, extra-resource biomass production and distribution, as quantified by box-count fractal dimension. When mycelia grew from 0.5 cm3 beech (Fagus sylvatica) wood inocula across compressed, non-sterile soil to 0.06-4 cm3 uncolonised sterile beech wood 'baits' extension rate fell after contact with large wood baits but biomass production and mycelial distribution was unaffected. In contrast, extension rates of cord systems grown from 0.15 cm3 U. dioica rhizome inocula to 0.1- 1.2 cm3 rhizome 'baits' were unaffected after contact with equal or larger sized baits, but biomass production rates fell and mass fractal dimension increased. Mycelial morphology was affected by inoculum age; systems grown from 84 day old 0.5 cm3 beech wood inocula took 10 days longer achieving the fractal values of systems developing from 22 day old inocula. Foraging strategies and resource relations of mycelial cord systems are discussed.
Uptake of 32P phosphorus from soil was investigated in mycelial cord systems of Phanerochaete velutina, Hypholoma fasciculare, Tricholomopsis platyphylla and Phallus impudicus which extended from 0.5, 2, 4 or 8 cm3 beech (Fagus sylvatica) inocula. Cord systems accumulated between 4.8 and 18.7% of phosphorus supplied to soil, according to species and size of inoculum. Phosphorus translocation to newly-colonized 2 cm3 beech baits, determined non-destructively, was characterized by an initial steady phase, of 2.5 to 32 nmol P day-1 which lasted at least 12 days for all four species. After the initial steady phase, translocation rates declined. Initial mycelial extension and wood decay rates also varied with species and inoculum size. There was no clear relationship between phosphorus translocation rates, wood decay or the distribution of soil-derived phosphorus in cord system components. However, with increasing inoculum size, P. velutina systems allocated a significantly greater proportion of available phosphorus to newly-colonized baits. The degree to which distribution of soil-derived phosphorus in cord systems is related to nutrient conservation or metabolic demand in the fungi is discussed.
The structure of a fungal colony growing on an agar surface has been shown to follow a fractal model. This report investigates the fractal dimensions of subsurface colonies of a transformed strain of Gliocladium virens (GvT6) and the unaltered strain (Gv29-8). Strain GvT6 contains the opd gene from Flavobacterium sp. Fractal analysis of GvT6 and Gv29-8 should indicate changes in the branching character of a fungus due to genetic modification. A system was developed to capture microscopic images of a growing fungal colony in the subsurface of ground lignite. Images were taken at two-day intervals over a six-day period. A combination of image processing algorithms gave binary images of each fungal colony at each sampling time. The fractal dimensions of the colonies were determined from analysis of these images. Our research showed the fractal dimensions of colonies of GvT6 and Gv29-8 were indistinguishable, which indicated the two strains displayed similar branching characteristics. The fractal dimensions of both strains changed from 1.334 to 1.854 as the colonies matured, indicating more homogeneous coverage within the area colonized. Other researchers have found similar fractal dimensions for other fungal species. The radial extension rate of GvT6 was less than that of Gv29-8, which indicated strain GvT6 colonized the subsurface matrix at a slower rate than Gv29-8, even though the branching pattern was similar.
Uptake of 32P phosphorus from soil was investigated at 5–25 °C in mycelial cord systems of Phanerochaete velutina (D.C.: Pers.), Hypholoma fasciculare (Huds.: Fr.) Kummer and Phallus impudiciis (L.) Pers. which extended from 2cm3 beech (Fagus sylvatica) inocula, and which had initially developed at either 10 or 25 °C. Uptake of phosphorus from soil was opportunistic, being unaffected by the presence of additional wood resource units in mycelial cord systems. The magnitude of phosphorus uptake was dependent on species, temperature during uptake and the temperature at which cord systems developed. Phosphorus translocation to newly colonized baits, determined non-destructively, was characterized by an initial rapid flux to a plateau in all three species. Initial rates of phosphorus translocation (up to 18·46 nmol P d-1) generally increased with temperature whilst total translocation was species and temperature dependent. There was evidence that both P. velutina and H. fasciculare displayed temperature acclimation, since phosphorus uptake and translocation at lower temperatures was greater in cord systems which had developed initially at 10° compared with 25 °C. Mycelial extension and wood decay rates also varied with species, initial development temperature and subsequent incubation temperature, but did not correlate with the temperature profiles of phosphorus uptake and translocation. Results are discussed in relation to nutrient acquisition, conservation and cycling in basidiomycete mycelial cord systems.
Mycelial cord systems, of the basidiomycete Phanerochaete velutina, a common woodland saprotroph, were grown on unsterile soil in model laboratory microcosms from 4 cm3 wood inocula. Systems were supplied after 37 d with a fresh 4 cm3 beech wood ‘bait’, placed behind the foraging colony margin. Systems were subject to dry shift (— 0.056 MPa) or wet shift (— 0.009 MPa) over an 11d period either immediately after, or 20 d after baits were supplied. Controls were maintained at constant soil matric potential (— 0.019 MPa). 57-d-old systems were supplied with NH4K2PO4 including 32P tracer within soil compartments local to inoculum or bait. Image analysis was used to quantify morphological responses to water regime and resource supply, and tracer movement monitored non-destructively with a scintillation probe for 57 d. 32P uptake was greatest when tracer was supplied local to the inoculum. Dry shift concurrent with bait supply caused system wide cord-thickening, prevented polarised growth towards the newly supplied bait, had a significant carbon (energy) cost compared to controls, significantly reduced 32P acquisition, and significantly increased 32P relocation to the bait. Wet shift concurrent with bait supply caused considerable loss of extra-resource mycelium in the unbaited region, resulting in highly polarised development along the bait-inoculum line, but did not affect 32P uptake and partitioning. Delayed wet shift caused swifter polarisation towards the bait, quantified in terms of fractal dimension, did not result in system wide regression of extra-resource mycelium, and resulted in correspondingly increased rates of 32P acquisition. Delayed dry shift prevented polarised growth towards the bait and had only transient effects on 32P uptake and partitioning. Results suggest that resource capture took priority over coordination of C reserves and reallocation of mycelial effort, and that mycelium colonising the new resource was more dependent on P translocate during desiccation stress.
A technique is described which enables high resolution images of the distribution of individual hyphae within fungal mycelia to be obtained, when the fungi are growing in nutritionally heterogeneous environments. The basis of the technique is to project colonies grown on the surface of cellulose membranes onto high contrast film using a photographic enlarger. Heterogeneity of nutrient resources is controlled by overlaying the membrane onto the surface of a box designed to hold disposable pipette tips, where the holes designed to hold the tips have been filled with gels of contrasting nutrient status. The effect of regular and irregular patterns of relatively high and low nutrient status gels upon development of single mycelia of Trichoderma viride and Rhizoctonia solani is shown. The technique can readily image mycelia up to 30 cm2 whilst still permitting resolution of individual hyphae where nutrient supply is sufficiently low to result in low hyphal densities.
Uptake of 32P phosphorus from soil was investigated in mycelial cord systems of Phanerochaete velutina, Hypholoma fasciculare, Tricholomopsis platyphylla and Phallus impudicus which extended from 0.5, 2, 4 or 8 cm3 beech (Fagus sylvatica) inocula. Cord systems accumulated between 4.8 and 18.7% of phosphorus supplied to soil, according to species and size of inoculum. Phosphorus translocation to newly-colonized 2 cm3 beech baits, determined non-destructively, was characterized by an initial steady phase, of 2.5 to 32 nmol P day−1 which lasted at least 12 days for all four species. After the initial steady phase, translocation rates declined. Initial mycelial extension and wood decay rates also varied with species and inoculum size. There was no clear relationship between phosphorus translocation rates, wood decay or the distribution of soil-derived phosphorus in cord system components. However, with increasing inoculum size, P. velutina systems allocated a significantly greater proportion of available phosphorus to newly-colonized baits. The degree to which distribution of soil-derived phosphorus in cord systems is related to nutrient conservation or metabolic demand in the fungi is discussed.
Two-dimensional image analysis was applied to counting, sizing, and density determinations of granules in full-scale and laboratory-scale upflow anaerobic sludge blanket (UASB) digesters. An advantage of this technique for monitoring laboratory-scale digester sludge is the small amount of material required for analysis. Quantification of number of granules using this method correlated well with dry weight determinations (r = 0.989). Distinguished granule size increased with time throughout the digestion process, supported by dry weight determinations which indicated an increase in biomass. The monitoring of granule density may reveal subtleties of the selection pressure placed on granules not noticed previously. © 1993 John Wiley & Sons, Inc.
The fractal geometry of foraging mycelial systems of Phanerochaete velutina and Hypholoma fasciculare, extending into soil from woody resource bases of varying nutrient status, was determined. The degree of structural heterogeneity and branching of systems, as described by the fractal dimension, was greater when the nutrient status of the resource base was high. H. fasciculare produced more-branched, slower-extending systems, with a greater commitment of mycelial biomass to exploration than P. velutina. The potential use of fractal geometry as a descriptor of foraging strategies of cord-forming, saprotrophic basidiomycetes, and the possible mechanisms operating to generate fractal growth in these systems are discussed.
Abstract Saprotrophic mycelial-cord-forming basidiomycetes, which extend between organic substrata on the forest floor, exhibit remarkable patterns of reallocation of biomass and nutrients when encountering new resources. These have been equated with foraging strategies, and differ between species, resources quality and quantity. Stropharia caerulea occupies more disturbed sites than the fungi previously examined, and the responses of its mycelial foraging systems were investigated non-destructively by image analysis. Resource quantity and quality affected extension rate, extra-resource biomass production and distribution, as quantified by box-count fractal dimension. When mycelia grew from 0.5 cm3 beech (Fagus sylvatica) wood inocula across compressed, non-sterile soil to 0.06-4 cm3 uncolonised sterile beech wood "baits" extension rate fell after contact with large wood baits but biomass production and mycelial distribution was unaffected. In contrast, extension rates of cord systems grown from 0.15 cm3 U. dioica rhizome inocula to 0.1-1.2 cm3 rhizome "baits" were unaffected after contact with equal or larger sized baits, but biomass production rates fell and mass fractal dimension increased. Mycelial morphology was affected by inoculum age; systems grown from 84 day old 0.5 cm3 beech wood inocula took 10 days longer achieving the fractal values of systems developing from 22 day old inocula. Foraging strategies and resource relations of mycelial cord systems are discussed.
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.
A number of saprotrophic fungi, particularly wood-decaying basidiomycetes, from mycelial cords, which are aggregations of predominantly parallel, longitudinally aligned hyphae. These linear organs often form extensive, long-lived systems which connect between discrete nutrient resources on the floor of temperate and tropical forests, and can form nets in tropical canopies.They are a very successful group of decomposers which exhibit many strategies analogous to those adopted in warfare, including: securing territory by aggressive/combative action; economic and efficient discovery of potential resources; establishing lines of communication; economic and efficient deployment of resources; and adoption of different strategies according to the home economic situation. Thus, nutrients are sequestered by foraging mycelial fronts and translocated to different parts of the mycelial system. On encountering new resources mycelial biomass and nutrients may be reallocated depending on a number of factors including: the relative size of inoculum base and new resources, state of decay of resources, whether the new resource is already colonized, the relative positioning of one new resource compared with another, and the fungal species involved.Cord-forming saprotrophic fungi probably play a major role in ecosystems, since they are major wood decomposers and can translocate large quantities of essential nutrients over several metres. They may, however, immobilize nutrients for considerable periods, perhaps months or longer, but by so doing may act as a buffer against nutrient loss from the system. The ease with which they can be inoculated into the forest floor could possibly be used as a management tool by virtue of their antagonism to tree root pathogens and their abilities as agents of nutrient cycling and translocation.
Immunoblotting combined with computer imaging and a simple, non-linear mathematical model were used to demonstrate the potential of a technique for non-destructive visualisation and analysis of fungal growth of Rhizoctonia solani over the surface of non-sterile sand. Immunoblotting detected actively growing regions of mycelium enabling visualisation of individual hyphae at the colony edge. A zone of active growth was detected expanding radially over time. Active growth did not continue in the centre of the fungal colony leading to the development of a ring of mycelium surrounding the inoculum. Change in the density of actively growing mycelium with distance from the inoculum unit was summarised for each colony at each time by a Gaussian function, describing a wave of actively growing mycelium, symmetrical in density about its centre but differing amongst replicate colonies. The effectiveness of the immunoblotting technique to detect differences in colony growth was tested by comparing the growth of replicate colonies for two contrasting isolates of R. solani. When both isolates of R. solani were grown at 23 °C the amplitude of the wave increased to a maximum and then decayed over time, the location of the centre of the wave moved outwards at a constant rate, whilst the width of the wave increased. Increasing the temperature to 28°, accelerated this intrinsic growth process for one isolate, but retarded growth of the other.
Effect of temperature and water potential on extension rate, extra-resource biomass and fractal dimension of Stropharia caerulea and Phanerochaete velutina growing in trays of soil was determined non-destructively with time, by image analysis. S. caerulea responded differently from P. velutina, mycelial extension and biomass production rates of the former being considerably affected by changes in temperature and water potential, with greater aggregation of mycelia into cords at 25°C and at and below -0.02 MPa. These morphological changes were reflected in the fractal dimension values. Mycelial extension of S. caerulea on agar was sensitive to temperatures above 25° and water potentials below -1.3 MPa. This is the first reported work on abiotic effects on fractal dimension of cord-forming fungi on soil, and these results are discussed in terms of the function of mycelial cords and foraging strategies.
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