Maximised photosynthetic capacity and decreased hydraulic failure risk during aging in the clump bamboo, Bambusa chungii.

To assess the water use of a clumped bamboo species, we investigated water use, physiological responses and structural changes related to culm aging in the clumped bamboo species Bambusa chungii McClure. Anisohydric behaviour was characterised by the independent stomatal conductance (gs) to leaf water potential (ΨL), and the low stomatal sensitivity (-m) in the young (0.52) and mature groups together with the aged group (0.41): gs was negatively related to intercellular CO2 (Ci), especially during the dry season (R2=0.62). Hydraulic conductivity (ks) decreased by 57.9 and 58.8% in the mature and aged groups. This was accompanied by a leaf area (AL) decrease of 55.7 and 63.7% and a water transport path (h) reduction of 8.5 and 23.3% to maintain the hydraulic safety. The net photosynthetic rate (An) was similar among the three age groups even during the dry season when water deficits occurred. The observed increase in chlorophyll content (5.3% greater for the mature group) and stomata density (7.4 and 8.1% greater for the mature and aged groups) with age might compensation the reduced whole culm carbon assimilation caused by decreased AL. Physiological and structural regulation contributes to the fitness of B. chungii.