Nine trees of Cryptomeria japonica from six elite tree clones with a broad range of heartwood colors were selected. The profiles of pit aspiration percentage (ASP) of earlywood and latewood from pith to bark for green and air-dry conditions were determined to study the relationship between heartwood color and pit aspiration. Confocal laser scanning microscopy (CLSM) observations showed that the ASP of earlywood was low in sapwood and high in heartwood in the green condition. Pit aspiration increased in intermediate wood when compared with sapwood. On the other hand, latewood pits did not aspirate during heartwood formation. Comparing the air-dry condition with the green condition, sapwood pits aspirated during drying in both earlywood and latewood; however, there was no significant difference in pit aspiration of heartwood. There was no significant difference between samples with red and black heartwoods for ASP. The difference in ASP between individual trees was larger than that by heartwood color. The general advantage of CLSM over light microscopy is that serial optical sections along the Z axis can be obtained for any moisture condition, without the need for thin sectioning or embedding.
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