Lichen substances affect metal adsorption in Hypogymnia physodes

Area of Science:

• Biogeochemistry
• Environmental Science
• Mycology

Background:

• Lichen substances are recognized for their cation-chelating properties.
• Previous research indicated increased physodalic acid production in Hypogymnia physodes under heavy metal pollution.
• A mechanistic link between lichen substances and metal uptake control was hypothesized.

Purpose of the Study:

• To test if lichen substances control toxic metal uptake via adsorption at cell wall cation exchange sites.
• To investigate the specific effects of four lichen substances on cation adsorption.
• To provide a mechanistic explanation for observed pollution tolerance in lichens.

Main Methods:

• Cellulose filters, mimicking lichen cation exchange, were treated with four lichen substances: physodic acid, physodalic acid, protocetraric acid, and atranorin.
• Treated filters were exposed to solutions containing seven different cations (Ca(2+), Cu(2+), Fe(2+), Fe(3+), Mg(2+), Mn(2+), and Na(+)).
• Changes in cation concentrations in the solutions were measured to quantify adsorption.

Main Results:

• Physodalic acid significantly influenced metal adsorption, increasing Fe(3+) uptake.
• Physodalic acid reduced the adsorption of Cu(2+), Mn(2+), and Na(+), and to a lesser extent, Ca(2+) and Mg(2+).
• Observed reduced Na(+) adsorption correlates with Hypogymnia physodes' known tolerance to NaCl.

Conclusions:

• Lichen substances play a role in controlling cation and toxic metal uptake.
• Physodalic acid's specific adsorption effects suggest a mechanism for metal homeostasis in lichens.
• These findings support a general role for lichen substances in mediating metal homeostasis and enhancing pollution tolerance.