The oxygen supply to thermogenic flowers

Thermogenic flowers produce heat by intense respiration, and the rates of O₂ consumption (?o₂) in some species can exceed those of all other tissues of plants and most animals. By exposing intact flowers to a range of O₂ pressures (Po₂) and measuring ?o₂, we demonstrate that the highest respiration rates exceed the capacity of the O₂ diffusive pathway and become diffusion limited in atmospheric air. The male florets on the inflorescence of Arum concinnatum have the highest known mass‐specific ?o₂ and can be severely diffusion limited. Intact spadices of Japanese skunk cabbage Symplocarpus renifolius are diffusion limited in air only when ?o₂ is maximal, but not at lower levels. True flowers of the sacred lotus Nelumbo nucifera and the appendix of Arum concinnatum are never diffusion limited in air. ?o₂ – Po₂ curves are evaluated quantitatively with the ‘Regulation Index’, a new tool to measure dependence of ?o₂ on ambient Po₂, as well as the conventional ‘Critical Po₂’. The study also includes measurements of Po₂ within thermogenic tissues with O₂‐sensitive fibre optics, and reveals that the diffusion pathway is complicated and that O₂ can be provided not only from the surface of the tissues but also from the pith of the flower's peduncle.