CONICET | Buscador de Institutos y Recursos Humanos

Fungi are the main decomposers of lignocellulose in temperate forests and are classi-fied as either white- or brown-rot, based on the ability to degrade lignin along with cellulose and hemicellulose. In this work, the decomposition of Nothofagus pumiliowood by different wood-inhabiting fungal species was investigated through in vitroassays. Sapwood and heartwood blocks were individually exposed to 11 fungal spe-cies; the dry mass loss was determined after 75, 135, and 195 days of exposure, com-paratively analyzing the fungal ability to colonize and degrade this lignocellulosic substrate corresponding to both parts of the wood. Transverse sections of the blocks were made and separately stained with two types of dyes, Congo red and phloroglu-cinol, that are specifically associated with cellulose and lignin, respectively. Most of the species showed a different performance in sapwood and heartwood. Rhizochaete brunnea, Aurantiporus albidus and Phanerochaete velutina produced the greatest mass losses in the sapwood. The last two and Laetiporus portentosus produced the highest dry mass losses in heartwood, while Rh. brunnea was among the worst decompos-ers of this substrate. White rots generally showed a higher ability to degrade the sapwood and brown rotters the heartwood. The fungal species producing greater dry mass losses in heartwood than in sapwood grow on heartwood of living trees. Among white-rot fungi, two modes of action were identified: a) localized degrada-tion, with zones of advanced decay in a less deteriorated matrix, and b) homogeneous degradation, with uniform decay. Our results showed that many species have dif-ferent performances in different substrates, reinforcing the importance of analyzing sapwood and heartwood decomposition separately, something not usually done in this kind of studies.

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