Strain Changes on the Inner Bark Surface of an Inclined Coniferous Sapling Producing Compression Wood

Abstract

Summary The tangential strain on the inner bark of Cryptomeria japonica saplings grown in a growth chamber was continuously measured using strain gauges. Compression wood formation was induced by artificial inclination. The diurnal changes in tangential strain during light/dark cycles in the growth chamber differed from those observed in the field. The total strain increased daily, increasing incrementally during dark periods and decreasing in the light, as observed in the field. In the growth chamber, however, steep increases and rapid decreases in strain were found immediately following lights-off and lights-on. In the inclined saplings, the strain increased more on the lower side of the stem than on the upper side; and the increment of the strain in the dark and the decrement in the light were larger on the lower side than on the upper side. The change in tangential strain on the inner bark surface arises from changes in the volume of differentiating cells, corresponding to turgor pressure changes and cell-wall extensibility changes. Therefore, the differentiating tracheids into compression wood appear to expand at night and shrink in the daytime more than the differentiating tracheids into normal wood.