Objective The objective of this paper is to analyze quantitatively the leaf predawn water potential change with the growth season and age along canopy height for moso bamboo (Phyllostachys edulis) in natural and drought stress environment, and to clarify the seasonal differences of water supply for individuals of different ages of Ph. edulis, lay a theoretical basis for the sustainable and efficient management of Ph. edulis plantations in the global climate background.

Method The throughfall exclusion was set to simulate the drought stress, and the PSYPRO water potential measurement system was used to quantitatively analyze the trend of leaf water potential change in the predawn with the growth season and bamboo age.

Result (1) There was significant difference among different seasons for leaf predawn water potential for the same age of bamboo (P < 0.05), regardless of throughfall exclusion or not. (2) The leaf predawn water potential changing with the growth season showed a peak trend for the same age of bamboo, and was different due to bamboo age. Under natural growth environment (the control), the predawn water potential for 1-and 7-year-old bamboo changing with the seasonal showed a single peak with the highest value in September, and for 2-to 5-year-old individual it showed a bimodal change trend with the highest values in September and December respectively. The seasonal change trend of leaf predawn water potential was consistent with the soil moisture. After the throughfall exclusion, the leaf predawn water potential was "double peak" type for 1-and 2-year-old individual, and was "single peak" type for 3-to 5-year-old individual, which changed with the seasons. (3) The change with increasing age of bamboo for leaf predawn water potential under throughfall exclusion environment was similar to that of the control during different growth season. Regardless of throughfall exclusion or not, the leaf predawn water potential decreased with the increase of bamboo age during the rhizome vigorous growth season from August to October, and showed the trend of the water transport from young bamboos to old ones, while the leaf predawn water potential increased with the increase of bamboo age during the shoot development period from October to March the following year, and the water transported from the high water potential of old bamboo to low water potential of young ones, indicating that the water supply direction between different age of bamboo individuals changed in different season. (4) During the vigorous growth of rhizome, the leaf predawn water potential under throughfall exclusion was significantly lower than that under natural growth environment, and the difference in leaf predawn water potential became more significant with the increase of bamboo age. Under throughfall exclusion, only the leaf predawn water potential of the bamboo with the age over 5-years-old was lower than the control during the shoot development period. (5) There were no significant differences in predawn water potential of different canopy leaves in different growth seasons, but the change trend of leaf water potential was also affected by the bamboo age.

Conclusion There was a significant seasonal difference of leaf predawn water potential for same aged individual. Both the leaf predawn water potential and the soil moisture follow same seasonal change trend. The transport direction of water between different age of bamboo individuals varied with season, indicating that the leaf predawn water potential is an important factor in driving the bamboo to adapt to drought stress.