Age- and stage-dependent water use traits of rhizome-connected clonal ramets in Moso bamboo (Phyllostachys edulis (Carrière) J. Houz) in subtropical China

Moso bamboo ( Phyllostachys edulis ) is a rhizome-integrated clonal species and one of the most important industrial forest crops in subtropical China. However, age-dependent water-use characteristics among rhizome-connected culms and their variations across shoot developmental stages remain poorly understood. To address this knowledge gap, we investigated water-use traits of interconnected newly sprouted culms (NC) and established culms (EC) from August 2023 to January 2024, encompassing the shoot bud differentiation stage (Stage I) and bud enlargement stage (Stage II). Sap flow rate (SF), diurnal and nocturnal water use, transpiration (Tr), midday leaf water potential, stomatal conductance, and instantaneous leaf water-use efficiency (WUE leaf ) were quantified along with key environmental drivers. During stage I, NC exhibited substantially greater water use than EC. Mean SF in NC was 429.58% higher than in EC, while mean daily Tr reached 3.49 kg d −1 in NC compared with 0.94 kg d −1 in EC. NC also showed greater daytime stem water withdrawal and higher stomatal conductance, whereas EC maintained a larger nocturnal contribution to total daily sap flow. In Stage II, however, SF and Tr in NC declined sharply by 87.97% and 84.47%, respectively, relative to Stage I. Significant differences in WUE leaf between NC and EC emerged during this stage. Across culm ages, Tr was positively correlated with vapor pressure deficit and solar radiation, with the strongest relationships observed in NC during Stage I. Environmental variables explained a substantially greater proportion of variation in Tr in NC than in EC. These results demonstrate pronounced age- and developmental stage-dependent differences in water-use traits among rhizome-connected Moso bamboo culms. The findings improve our understanding of physiological integration and water-use strategies in clonal bamboo systems and provide a physiological basis for age-structured and season-specific water management in bamboo forests.