Effect of diurnal change of turgor pressure on wood formation

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The aim of this research was to establish a method of detecting the diurnal change of turgor pressure in the living cells of tree by using the strain gage and also to understand the relation between the turgor pressure and the secondary growth of the tree.The diurnal change of the tangential strain in the inner bark was measured, leading to the following results.1, Under the natural light condition, the tangential strain in the inner bark of the tree trunk showed a maximum shrinkage at about two o'clock in the afternoon, expanding gradually later in the afternoon until night-time. The maximum expansion was observed before the daybreak and during the day period a sudden shrinkage was appreciated at the same time when the sunshine started.The tangential strain measured in a growing chamber with controlled artificial lighting made clear that the diurnal change of the strain coincided with the change of sunlight illumination.2, The tangential strain had a high correlation with the water po … More tential measured in the leaves measured with a psychrometer.3, The tangential strain observed under the maximum shrinkage condition, was suddenly released when the leaves were removed or topping was done. Tangential strain shrinks corresponding to large water stress.During the process of withering, the shrunk strain did not recover even after water was supplied once the water potential became less than -1.5MPa. Two steps were recognized in the shrinkage process of the tangential strain. The strain shrunk up to the point when protoplasm separation would be occurred in the cell stops to shrink and start again to shrink by further drying.4, From the above results, it was clear that the diurnal change of tangential strain was due to the change in turgor pressure of living cells generated by the change in negative water pressure induced by both, transpiration and imbibition.5, The calculation made from the data of tangential strain and Young's modulus of the inner bark gave a value of 0.3-0.4MPa as the turgor pressure of living cells. The amount of diurnal change of the turgor pressure was estimated at 16-88Kpa.In this research, a method of continuous measurement of turgor pressure of living cells related to water potential was developed.Further research will enable to understand the generation process of the physical properties of wood in relation to the cell wall formation. Less