Heat production by sacred lotus flowers depends on ambient temperature, not light cycle

Flowers of the sacred lotus, Nelumbo nucifera, maintain receptacle temperature (Tr) between about 30°C and 36°C during their 2–4 d sequence of anthesis by increasing the rate of heat production, measured as oxygen consumption (Vo2), at low ambient temperature (Ta) at night and reducing it at high Ta during the day. The effects of Ta and photoperiod on Vo2 were separated by manipulating Ta around outdoor flowers under natural photoperiod or constant darkness. There was no effect of time of day on either Tr or Vo2, but both depended on Ta. Rising Ta resulted in an increase in Tr, a brief upward spike in Vo2, followed by a long-term decrease in Vo2. Decreasing Ta had the opposite effects: a decrease in Tr and a brief depression, followed by a slow rise, in Vo2. The two-phase responses to sudden Ta change indicate a rapid, massaction effect and a slower, regulatory adjustment. Temperature regulation continued in constant darkness for over 3 d.