The world's smallest rotary motor. See Box 11.1 . It may also be an energy spill-over system, when the main electron flow path is saturated. Read p 304-305 for info on alternate oxidase. O 2 in air-equilibrium solution.
Situation becomes worse in hydroponic solution or flooded soils.
Respiration is temperature dependent. Still debated - not always seen. Water replaces soil air - reduces O2 diffusion. Results in fermentation. Pneumatophores, aerenchyma, lacunae, in flood-tolerant species.