Persistence of the gelatinous layer within altered tension-wood fibres of beech degraded by Ustulina deusta

The gelatinous layer (G-layer) of tension-wood fibres in reaction wood of b eech showed alterations as a result of the physiological processes involved in the conversion of sapwood into false heartwood or reaction-zone tissue. Using transmitted-light, fluorescence and UV microscopy, polyphenolic comp ounds were found to infiltrate and encrust the cellulose microfibrils withi n the G-layer. Experiments with naturally infected and artificially inocula ted wood showed that these processes affect the rate and mode of degradatio n by wood-decaying fungi. Thus, although the ascomycete Ustulina deusta was able to degrade the G-layer from within the lumina of tension-wood fibres in unaltered sapwood, it failed to do so for a prolonged period within fals e heartwood and reaction zones. In both situations, however, there was some degradation of the underlying secondary wall in the form of erosion trough s which can be attributed to soft rot 'type II', and internal cavity format ion typical for 'type I' attack. The present study indicates that not only cell type, but also alterations in the cell wall structure, affect the acti vity and degradation mode of decay fungi in beech.