Respiration in low oxygen partial pressures: The adults of Donacia simplex that respire from the roots of aquatic plants

Abstract

The adults of Donacia simplex are found on the roots of aquatic plants during the winter. Oxygen diffuses from the gas spaces in the roots into the gas-filled cocoons through the root scar. The root scar slows down the diffusion of oxygen into the cocoons. During the winter the adults have a lower oxygen uptake between 4 and 14°C than do the emerged adults found in June. In January the respiratory rate does not vary much at different temperatures, but later in the year the QO 2 increases progressively above 8°C. The adults emerge from their cocoons when kept at 11 and 14°C in the laboratory. Adults with a high respiratory rate have a higher critical oxygen pressure than adults with a lower oxygen uptake. At low oxygen pressures (0·1 per cent) the oxygen uptake was found to be the same whatever the initial oxygen uptake in air. Adults responded to 3 days' exposure to lowered oxygen pressures (1 and 0·1 per cent) in two ways. The oxygen uptake may be depressed after the exposure to the lowered oxygen conditions compared with the initial rate in air or an oxygen debt may be accumulated. The response depended on the initial QO 2 in airand the pO 2 experienced. The adults appear to be adapted to respiration in low oxygen pressures (commonly met with on the roots of the plants during the winter) but not to the complete absence of oxygen. The respiration rate in response to temperature can be related to the temperatures likely to be encountered and the oxygen supply from the roots.