Carbon balance: A technique to assess comparative photosynthetic physiology in poikilohydric plants.

Premise: Poikilohydric plants respond to hydration by undergoing dry–wet–dry cycles. Carbon balance represents the net gain or loss of carbon from each cycle. Here we present the first standard protocol for measuring carbon balance, including a custom‐modified chamber system for infrared gas analysis, 12‐h continuous monitoring, resolution of plant–substrate relationships, and in‐chamber specimen hydration. Methods and Results: We applied the carbon balance technique to capture responses to water stress in populations of the moss Syntrichia caninervis, comparing 19 associated physiological variables. Carbon balance was negative in desiccation‐acclimated (field‐collected) mosses, which exhibited large respiratory losses. Contrastingly, carbon balance was positive in hydration‐acclimated (lab‐cultivated) mosses, which began exhibiting net carbon uptake <15 min following hydration. Conclusions: Carbon balance is a functional trait indicative of physiological performance, hydration stress, and survival in poikilohydric plants, and the carbon balance method can be applied broadly across taxa to test hypotheses related to environmental stress and global change. [ABSTRACT FROM AUTHOR]