Obligate crassulacean acid metabolism (CAM) plants survive karst drought through daytime stomatal closure, which limits water loss but suspends gas exchange, raising the question of how intracellular metabolism continues under closed stomata. Using a reintroduced population of the orchid \textit{Dendrobium loddigesii} shaped by 15 years of natural selection, we combined a two-season (January and April) between-population comparison with concurrent within-plant comparisons of different-aged leaves, and quantified leaf electrophysiology using an extended Hodgkin-Huxley model. Intracellular water transport rate (WTR) was highly conserved across seasons and leaf ages (overall mean \WTRall, withi... More >