Respiratory metabolism in mangrove seedlings

Area of Science:

• Plant Physiology
• Environmental Science
• Biochemistry

Background:

• Mangrove seedlings exhibit complex respiratory responses to varying oxygen and carbon dioxide levels.
• Understanding these gas exchanges is crucial for assessing mangrove resilience in changing environmental conditions.

Purpose of the Study:

• To investigate the impact of external carbon dioxide (CO2) on the respiratory gaseous exchanges of whole mangrove seedlings.
• To characterize the anaerobic and micro-aerobic respiratory pathways in mangrove seedlings under different oxygen concentrations.

Main Methods:

• Detached whole mangrove seedlings (Avicennia, Bruguiera, Rhizophora) were exposed to a range of oxygen concentrations (0-21%).
• Respiratory CO2 output, respiratory quotient (RQ), and the accumulation of fermentation products (ethanol, acetaldehyde, lactate) were measured.
• Experiments included conditions of anoxia, low oxygen (5-10% O2), and varying external CO2 levels, followed by a return to air.

Main Results:

• External CO2 markedly reduced respiratory gas exchange in whole mangrove seedlings.
• Under anoxia, CO2 output halved, with negligible ethanol but higher acetaldehyde; lactate accumulated then decreased.
• Low oxygen (5-10% O2) induced fermentation with RQ up to 1.4, but without ethanol, acetaldehyde, or lactate, suggesting alternative CO2 release pathways.
• Tissue slices showed reduced CO2 output in lowered oxygen, with RQ > 1 (except in air), and lacked the post-anoxic burst seen in whole seedlings.

Conclusions:

• Mangrove seedling respiration is sensitive to external CO2 levels, impacting gas exchange.
• Anaerobic metabolism in mangroves involves fermentation pathways that differ from the standard Embden-Meyerhof pathway.
• Tissue preparation methods (slicing) can alter observed respiratory mechanisms, particularly decarboxylation processes.