Switching off the heater: influence of ambient temperature on thermoregulation by eastern skunk cabbage Symplocarpus foetidus |
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Authors: | Seymour R; Blaylock A |
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Institution: | Department of Environmental Biology, University of Adelaide, Adelaide, S.A. 5005, Australia; Corresponding author e-mail: rseymour@zoology.adelaide.edu.au |
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Abstract: | The protogynous inflorescences of eastern skunk cabbage,
Symplocarpus foetidus, are thermogenic and regulate
spadix temperature (Ts) well above ambient temperature
(Ta). Continuous records of oxygen consumption, carbon
dioxide production, and temperatures of plants were made at a field site in
Canada. At Ta between 3-24 C, Ts ranged between
16-26 C, and the warmest inflorescences were
those in the receptive female or early pollen-bearing stages. Respiratory
rates of the 2-g spadices increased with declining Ta,
and reached a maximum of 0.54 mol
O2s-1 (0.73 ml min-1),
equivalent to 0.26 W of heat production. At Ta below
3°C, several inflorescences failed to maintain high
Ts and abruptly switched Ts to
near freezing. Some froze when Ta dropped to about
-10°C. Those that did not freeze could quickly switch to the warm
state if Ta rose above about 3°C. Switching
was related to the balance between heat production and heat loss that
tended to produce stable equilibria at either high or low
Ts. Switching between warm and cool states resulted in
a bimodal distribution of Ts in the field. A
respiratory quotient of 1.0 showed that carbohydrate was the substrate for
thermogenesis, and bomb calorimetry of florets confirmed that energy was
imported from the root. Only 11 invertebrates, including only one flying
insect, were found in 195 inflorescences, suggesting that heat production
and temperature regulation are not closely associated with
cross-pollination. |
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Keywords: | |
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