Resource relationships of foraging mycelial systems of Phanerochaete velutina and Hypholoma fasciculare in soil

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Inoculum blocks of wood colonized by the basidiomycetes Hypholoma fasciculare (Huds.: Fr.) Kummer and Phanerochaete velutina (DC: Pers.) Parmasto were placed in plastic trays containing moist (matric potential −0.007 MPa), unsterilized soil. When ‘baits’, in the form of beech (Fagus sylvatica L.) wood blocks, descaled pine (Primus sylvestris L.) cones, beech twigs, beech leaves or pine needles were introduced, H. fasciculare consistently responded by ramification of diffuse mycelium within and over the baits, inhibition of extension and regression of non-connective mycelium, thickening of connective cords and polarized outgrowth from the baits. Decay of inoculum wood blocks was generally greater in the control than where baits were added. Whilst the decay rates of different types of baits varied, pine cones being least decayed, total loss of dry weight from the system (inocula and baits combined) was similar in all cases. The sparser, more independent and rapidly extending cords of P. velutina exhibited more varied responses to the introduction of baits, and only under certain circumstances exhibited the same responses as H. fasciculare. Although decay of inoculum blocks was generally greater in controls than where colonizable baits were added, total loss of dry weight in the latter systems was two- to fourfold greater than in controls.

Snowflake-like mycelial growth patterns were induced in H. fasciculare by growing the fungus from an inoculum block placed in the centre of two concentric, hexagonal arrays of wood-block baits. Selective removal of baits from the inner hexagonal array, after they had been colonized but before renewed outgrowth from them, either greatly delayed colonization of outlying blocks, if all six were taken out, or led respectively to symmetrical or asymmetrical ‘bypass’ systems if three alternating or adjacent blocks were taken.

These observations are further support for the interpretation of basidiomycete mycelial cords as foraging systems and suggest experimental approaches which can help to elucidate their behaviour.

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