Patch formation and developmental polarity in mycelial cord systems of Phanerochaete velutina on a nutrient‐depleted soil

Abstract

S I" M M A R YDevelopmetit of mycelial cord systems of Phanerochaete velutina (DC.: Pers.) Parmasto from 4-cm^ inocuk on a nutrient-depleted non-sterile soil was studied in laboratory microcosms using image atialysis techniques. Cord systems were 'baited' after 13 d growth with either fresh, non-sterile 4-cm'' 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 systenis did not differ significantly (P > 0'05), patch cover in wood-baited systems was up to 10 times greater than in Perspexbaited 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. Woodbaited mycelial systems displayed significant developmental polarity (P ^ 0-05) 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 de\'elopment. 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 ^"P, 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.

Temporary phosphorus partitioning in mycelial systems of the cord‐forming basidiomycete Phanerochaete velutina

“…Laboratory studies have shown that mycelial cords and rhizomorphs (see Rayner et al, 1985 for discussion of morphogenesis) of saprotrophic, mycorrhizal and pathogenic basidiomycetes are pathways for translocation of water and solutes (Watkinson, 1971 ;Brownlee & Jennings, 1981, 1982Granlund, Jennings & Thompson, 1985 ;Finlay & Read, 1986 a, b ;Duddridge et al, 1988 ;Wells et al, , 1997Hughes & Boddy, 1994, 1996Timonen et al, 1996), the latter studies focusing both on the mechanism and functional significance of the process. Importantly, one study has confirmed that phosphorus is translocated between discrete litter components in field systems of three saprotrophic species Phanerochaete velutina, Phallus impudicus and Hypholoma fasciculare .…”

“…Furthermore we have usually supplied new wood resources to the actively foraging colony margin. Wells et al (1997) and Wells, Boddy & Donnelly (1998) showed, however, that mycelial systems could be maintained in laboratory microcosms for at least 6 months and retain their ability to respond developmentally to an input of new wood behind the foraging mycelial margin. This is important since, in the field, the environmental heterogeneity experienced by mycelial systems is manifest not only because utilizable resources are variable in quality and spatial distribution, but also because of temporal changes in resource availability.…”

“…They are major agents of litter decomposition, considered to have a significant influence on the cycling, relocation and availability of nutrients (Boddy, 1993 ;Boddy & Watkinson, 1995). These fungi display highly efficient foraging and resource exploitation strategies (Dowson, Rayner & Boddy, 1986Dowson et al, 1989 ;Bolton & Boddy, 1993 ;Donnelly, Wilkins & Boddy, 1995 ;Wells, Boddy & Evans, 1995 ;Wells, Donnelly & Boddy, 1997), are efficient scavengers of soil-derived minerals and are highly conservative of acquired nutrients Wells, Hughes & Boddy, 1990 ;Hughes & Boddy, 1994, 1996.…”

“…Here, using non-destructive image analysis techniques (Donnelly et al, 1995 ;Wells et al, 1997) we describe quantitatively the growth and development of large (50 cm diameter) mycelial systems of P. velutina in laboratory microcosms. We also investigate how temporally-discrete (simulated) litter inputs to established mycelial systems of P. velutina affect nutrient partitioning, testing the hypothesis that the litter colonization process is a driving force for phosphorus translocation.…”

“…Laboratory microcosms incorporate non-sterile soil and natural carbon sources (wood and leaf litter) which permit simulation of the heterogeneous conditions experienced by naturally occurring cord-forming fungi in the field. Rapid and non-destructive estimation of mycelial extension rates, biomass and changes in foraging pattern or growth form using image analysis techniques have highlighted the fractal nature of mycelial systems, yielding objective measures of foraging pattern (Donnelly et al, 1995 ;Abdalla & Boddy, 1996 ;Donnelly & Boddy, 1997 a, b ;Wells et al, 1997).…”