Switching off the heater: influence of ambient temperature on thermoregulation by eastern skunk cabbage Symplocarpus foetidus

The protogynous inflorescences of eastern skunk cabbage, Symplocarpus foeti dus, are thermogenic and regulate spadix temperature (T-s) well above ambie nt temperature (T-a). Continuous records of oxygen consumption, carbon diox ide production, and temperatures of plants were made at a field site in Can ada. At T-a between 3-24 degrees C, T-s ranged between 16-26 degrees C, and the warmest inflorescences were those in the receptive female or early pol len-bearing stages. Respiratory rates of the 2-g spadices increased with de clining T-a, and reached a maximum of 0.54 mu mol O-2 s(-1) (0.73 ml min(-1 )), equivalent to 0.26 W of heat production. At T-a below 3 degrees C, seve ral inflorescences failed to maintain high T-s and abruptly switched T-s to near freezing. Some froze when T-a dropped to about -10 degrees C, Those t hat did not freeze could quickly switch to the warm state if T-a rose above about 3 degrees C, Switching was related to the balance between heat produ ction and heat loss that tended to produce stable equilibria at either high or low T-s, Switching between warm and cool states resulted in a bimodal d istribution of T-s in the field. A respiratory quotient of 1.0 showed that carbohydrate was the substrate for thermogenesis, and bomb calorimetry of f lorets confirmed that energy was imported from the root. Only 11 invertebra tes, including only one flying insect, were found in 195 inflorescences, su ggesting that heat production and temperature regulation are not closely as sociated with cross-pollination.