Sap flow-based transpiration in Phyllostachys pubescens: applicability of the TDP methodology, age effect and rhizome role

We quantified the water use of Phyllostachys pubescens using 10 mm TDP. Water use of P. pubescens was affected by culm age rather than its size. Rhizome system has a strong transfer function. To accurately quantify the water use of bamboo forest stands, the applicability of a modified TDP (10 mm long) for measuring the sap flow of bamboo culms was verified. We also investigated the effects of culm age and rhizomes on water use. To this end, we designed two experimental systems, an induced hydraulic pressure and sap flow changing device and a whole-culm pot weighing method to validate the sap flow equation in Phyllostachys pubescens. The results showed that the modified 10 mm long TDP was a valid means of measuring the sap flow of P. pubescens. The verified probes and the corrected Granier’s empirical equation were applied to monitoring and calculating the sap flow density of P. pubescens. The results showed that stand transpiration changed significantly across the wet and dry seasons. Culm transpiration decreased with culm age whether in winter or in summer. Juvenile bamboo had the highest daily transpiration, and more than 20 % of compensative water was imported from other culms by rhizomes in summer. The water potential of the rhizome-cut culms was lower than that of normal culms. It is concluded that the rhizome system has a strong transfer function and that the water consumed by juvenile culms includes water self-absorbed directly from soil and water transferred from other culms via rhizomes.