Wood decay and phosphorus translocation by the cord‐forming basidiomycete Phanerochaete velutina: the significance of local nutrient supply

Abstract

Mycelial cord systems of Phanerochaete velutina (DC. : Pers.) Parmasto grown from 4 cm$ inocula on a nutrientdepleted non-sterile soil in compartmentalized laboratory microcosms were baited after 13 d of growth with either fresh, non-sterile 4 cm$ wood blocks or control Perspex2 blocks of the same contact area. After 112 d, mature mycelial systems, which were in senescent phase, were subjected to disturbance by supplying a new fresh wood bait diametrically opposite the existing bait and, after 126 d, to nutrient regime amendment by application of NPK solution. At harvest (186 d) there was a significant (P 0n001) linear relationship between extra-resource mycelial biomass and total wood decay over the preceding 74 d. Nutrient amendment alone did not significantly (P 0n05) affect extra-resource mycelial biomass production or wood decay rates in either disturbed or undisturbed cord systems. However, both mycelial biomass production and resource decay were significantly (P 0n05) enhanced when nutrient amendment and disturbance treatments were applied concurrently. Bi-directional phosphorus translocation to inocula and wood baits (determined non-destructively) was assessed by labelling the NPK solution applied distal or proximal to the initially supplied bait with $#P. In both disturbed and undisturbed cord systems the rate of $#P uptake from a local supply was two orders of magnitude higher than from a distal supply. In disturbed cord systems uptake of $#P by inocula, which were midway between the two radiotracer supply points, was significantly (P 0n05) higher when the supply point contained a newly supplied wood bait. Net translocation of $#P to newly supplied wood baits increased with time at the expense of translocation to inocula and existing wood baits. The switch in direction of net phosphorus translocation, the importance of localized nutrient scavenging and the partitioning of wood decay are discussed in relation to the ecological significance of mycelial cords.

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

“…Crucially, we have shown that phosphorus derived from soil in the vicinity of wood newly-colonized by P. velutina exceeds that supplied via translocation from other, previously-colonized, resources by 1-2 orders of magnitude (Wells et al, 1998), suggesting that nutrient translocation driven by demand due to the colonization process itself was unlikely. Why then does phosphorus translocation occur ?…”

“…Secondly, wood decay leads to shrinkage of the bait increasing the likelihood of β-particle scatter away from the scintillation probe window. It is for these reasons that we have previously recommended (Wells & Boddy, 1995 b ;Wells et al, 1997Wells et al, , 1998 that nondestructive counts should only be used to compare like resource units (i.e. those which have been on mycelial systems for the same length of time).…”

“…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.…”

“…Importantly, this result highlights that differential ' demand ' for phosphorus existed in the heterogeneous systems studied and could suggest that nutrient translocation might alleviate localized deficiency. However, as local (soilderived) mineral supply is far more significant to mycelium within wood (Wells et al, 1998), it seems possible that the observed translocation and partitioning of phosphorus indicates the degree to which this nutrient is likely to be loaded from a translocation stream in regions where it is being actively utilized and\or stored (i.e. the translocation stream could be analogous to the flow of an alternating current from which power is consumed only when the user plugs into the mains).…”

Translocation of 32P between interacting mycelia of a wood‐decomposing fungus and ectomycorrhizal fungi in microcosm systems

“…Many studies have indicated that decomposition of both wood (Merrill & Cowling, 1966 ;Thompson & Rayner, 1982 ;Wells et al, 1998), and needles and leaves (Aber & Melillo, 1980 ;Berg, 1986 ;Cotrufo et al, 1995 ;Cotrufo & Ineson, 1996), can be limited by access to mineral nutrients, particularly nitrogen. The microbial community of the mineral soil also has a high capacity to immobilize mineral nutrients (Stark & Hart, 1997).…”