Abstract: [Objective] This study aimed to test the suitability of TDP sensors with different lengths of probes to measure Moso bamboo (Phyllostachys edulis) sap flow and investigate the effect of age on the culm sap flow of Moso bamboo. Based on the measurements of individual culms, the transpiration water consumption of P. edulis forests in northern Guangxi, China was estimated by scaling up the sap flow of individual culms, which provided a basis for ecological and hydrological research of P. edulis forests.[Method] Microscope was employed to examine the hydraulic structure of Moso bamboo culm. The 5 mm-and 10 mm-length TDP probes were installed at the bottom of both 1-2 years old and above 3 years old ramet culms to monitor sap flow pattern at different time scales. Climate factors and soil water content were also measured synchronously.[Result] Vascular bundle were unevenly distributed in culm wall. The outer vascular bundles of the culm wall were small and dense, and the differentiation of the vessels was incomplete, while the inner vascular bundles of the culm wall were large and sparse, and the differentiation of the vessels was complete and the diameter was large. For the same culms, mean sap flow measured by 10 mm-length TDP probe was 3.03 times higher than that measured by 5 mm-length TDP probe, and the difference between them reached significant level. Based on the measurement of 10 mm-length TDP probe, the sap density of 1-2 years old culms was significantly higher than that of above 3 years old culms during midday time in July, while the sap density between them were nearly same during early morning and late afternoon. The daily sap flux in 1-2 years old culms was higher than that in above 3 years old culms during the measured growing season and the mean daily sap flux was 51.15 g·cm^-2 d^-1 and 33.80 g·cm^-2 d^-1 for 1-2 years old and above 3 years old culms, respectively. Considering culm age and diameter, the water use of Moso bamboo forest located in northern Guangxi was estimated based on culm sap flow. The up-scaled water use ranged from 0.01-0.72 mm·d^-1 with the average of 0.31 mm·d^-1.[Conclusion] The 10 mm-length TDP probe was more suitable for sensing sap flow of Moso bamboo than the 5 mm-length TDP probe. The 1-2 years old culm had higher maximal sap flow density and larger daily sap flux than those of above 3 years old culm. Thus culm age was another key factor that must be considered besides culm diameter in estimating stand-scale water use based on culm-scale sap flow measurement.

Key words: TDP, Plyllostachys edulis, age effect, up-scaling, water use