THE EFFECTS OF BISULPHITE AND SULPHATE UPON PHOTOSYNTHESIS IN SPHAGNUM

Area of Science:

• Environmental Science
• Plant Physiology
• Biochemistry

Background:

• Sphagnum mosses are crucial peatland ecosystem engineers.
• Sulfite (HSO3-) is an environmental pollutant with potential impacts on plant life.
• Understanding sulfite toxicity mechanisms is vital for assessing ecosystem health.

Purpose of the Study:

• To investigate the effects of sulfite (HSO3-) and sulfate (SO4^2-) on photosynthetic oxygen evolution in Sphagnum species.
• To determine the influence of sulfite concentration, pH, and bicarbonate (HCO3-) on oxygen production.
• To compare the sensitivity of oxygen evolution and carbon dioxide (CO2) fixation to sulfite exposure.

Main Methods:

• Controlled laboratory experiments exposing Sphagnum moss to varying concentrations of HSO3- and SO4^2-.
• Measurement of photosynthetic oxygen evolution and 14CO2 uptake under different conditions.
• Assessment of the impact of pH and HCO3- additions on physiological responses.

Main Results:

• Sulfite (HSO3-) caused rapid, concentration-dependent inhibition of oxygen evolution, which was not reversed by bicarbonate.
• Sulfate (SO4^2-) and sulfite (SO3^2-) had no significant effect on oxygen evolution.
• The inhibitory effect of HSO3- on oxygen evolution was more severe at lower pH levels.
• Carbon dioxide fixation was less sensitive to HSO3- than oxygen evolution, with low concentrations showing enhancement.
• Dark CO2 fixation was inhibited by 0.1 mM HSO3- but enhanced at lower concentrations.

Conclusions:

• Sulfite (HSO3-) poses a significant threat to Sphagnum photosynthesis, primarily by disrupting oxygen evolution.
• The pH-dependent nature of sulfite toxicity highlights the vulnerability of these plants in acidic environments.
• Differential sensitivity between oxygen evolution and CO2 fixation suggests specific biochemical targets for sulfite toxicity in Sphagnum.