Water sprinkled pine wood: A microscope study on boards showing streaking
G F Daniel, T Elowson, T Nilsson, A P Singh, K Liukko
Boards sawn from the outer sapwood of pine lumber previously water sprinkled for periods of 10-18 weeks and kiln dried, showed streaking after staining. Two types of enhanced stain uptake were noted: 1) a more concentrated and localized form after 10 weeks and 2) a more diffuse type which developed in later stages of water sprinkling. Areas showing enhanced stain uptake were examined using light and scanning electron microscopy. For all samples, staining was most concentrated in rays (both fusiform and uniseriate) and axial resin canals. Studies suggest that increased permeability and enhanced stain uptake results primarily from microbial (fungal and bacterial) destruction of rays and axial resin canals (i.e. ray parenchyma, epithelia cells, window pit membranes), either by direct attack (i.e. close proximity of bacteria/fungal hyphae) or by diffusion of enzymes (probably cellulases) from microbes distant from sites of hydrolysis. Sapwood offcuts from the outer regions of water sprinkled wood lacking bark showed severe colonization and decay of ray tissues by both bacteria and sapstain fungi. Diffuse stain uptake in boards at later stages of water sprinkling appeared to be secondary and result from bacterial and/or fungal decay of bordered pit membranes.
Keywords: WATER SPRINKED WOOD; PINUS SYLVESTRIS; BOARDS; ULTRASTRUCTURE; RAY PARENCHYMA; RAYS; RAY TRACHEIDS; WINDOW PITS; BORDERED PITS; PIT MEMBRANES; BACTERIA; FUNGI; DECAY; LIGHT MICROSCOPY; SEM