Objective  The objective of this study is to investigate the effects of brown-rot decay on color, microstructure, and chemical components of wood at the early stage of decay test, as well as provide a theoretical basis for the further explanation of wood degradation mechanism.

  Method  The sapwood of southern pine was decayed by Gloeophyllum trabeum for different durations. The microstructure of decayed wood was characterized by field emission scanning electron microscopy (FE-SEM), in order to elucidate the access pathways of brown-rot fungi into wood. Meanwhile, colorimetry, Fourier transform infrared spectroscopy and X-ray diffraction were used to characterize the mass loss, color change, chemical component, functional group change, and crystallinity change of wood after different decay stages.

  Result  The lightness of wood decreased and the total color difference increased during the decay test, with a trend toward rufous surface color. Mycelium entered into the wood through cell structures such as ray parenchyma cells, pits and tracheids, and basically completed the initial colonization after 20 d. The mass loss of wood at the early stage of brown-rot decay was mainly caused by the degradation of hemicellulose, while the degradation of cellulose was less pronounced. At the same time, the distance between crystal planes of cellulose decreased to the minimum value (3.962 Å) while the relative crystallinity increased significantly (47.02%), which prohibited the degradation of cellulose. Therefore, the mass loss rate of wood slowed down after that.

  Conclusion  At the early stage of brown-rot decay on southern pine wood, hyphae entered into wood by pits, ray parenchyma cells and tracheids. Hemicellulose in cell wall was preferentially degraded and the lattice distance of crystalline cellulose reduced while the relative crystallinity increased. This research could provide a theoretical basis for the further exploration of brown-rot degradation mechanism of wood, as well as wood preservation.