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Respiratory Metabolism in Mangrove Seedlings ¹

^a Botany Department, Auckland University, Auckland, New Zealand

The respiratory gaseous exchanges of detached whole mangrove seedlings (Avicennia, Bruguiera, Rhizophora) in a range of O₂ concentrations from 0 to 21% (air) were markedly reduced by the presence of external CO₂. Aerobic respiration decreased steadily for 16 days but the RQ remained at unity.

In anoxia CO₂ output fell to half that in air. Ethanol accumulation was negligible but, relatively, acetaldehyde values were higher than in other tissues. Lactate accumulated initially but later decreased. On return to air CO₂ output was elevated above control values in a pattern resembling the previous lactate accumulation. The extent of the burst was too great, and the RQ too low, to be explained entirely by lactate oxidation.

In 5 or 10% O₂ the CO₂ outputs were below those in anoxia and the RQ eventually rose to 1.4, suggesting the induction of fermentation. The absence of ethanol, acetaldehyde or lactate indicates that CO₂ was released from reactions other than those in the Embden-Meyerhof pathway.

Tissue slice CO₂ outputs decreased with lowered O₂ concentrations and the RQ was always above unity except in air. The burst on return to air was absent, suggesting that slicing affects decarboxylation mechanisms.