Strong emissions of carbon dioxide and water vapour by Sapria himalayana Griff. (Rafflesiaceae): waste or necessity in a cool flower?

Abstract

Due to respiration, the carbon dioxide present in the sapromyiophilous flowers of Sapria himalayana in its forest habitat in N Thailand was found to be five to nine times that of the ambient air. On the other hand, the emanation of carbon dioxide from a cadaver, the volatiles of which the flower mimics in its pollination syndrome, was not higher than that of the forest soil and thus in the ambient air near the ground, suggesting that the carbon dioxide is not part of the mimicry. This, and our preliminary finding that the carbon dioxide had neither attractive nor anaesthetic effects on the flower’s pollinators, the blowfly Lucilia porphyrina, indicates that the carbon dioxide essentially appears to be a waste by-product. Attraction is mainly by putrid volatiles. The water vapour in the flower’s tube of S. himalayana was found to be constantly close to saturation, even during the dry season when ambient minima averaged 40% RH. This resulted in the unexpected finding that while the flower was slightly thermogenic in humid ambient during the rainy season as in other Rafflesiaceae, it was constantly slightly cooler than the ambient during the dry season due to strong water evaporation. High humidity inside the flower is essential because the pollen can be acquired by the flies only in a fluid suspension.