Effects of sulfur dioxide exposure on leaf mass per area of selected gymnosperms and implications for interpreting the plant fossil record

Premise of research. The role of sulfur dioxide (SO₂) in plant responses to large igneous province volcanism is difficult to determine but important in relation to understanding ecosystem responses during mass extinction events. Leaf mass per area (LMA) is an important leaf measure for tracking plant responses to environmental pressures in the fossil record, but how it responds to SO₂ exposure is unclear, particularly for nonangiosperm taxa. Methodology. Five gymnosperm species were grown in simulated paleoatmospheric conditions that included SO₂ to determine how the plants responded. Pivotal results. All plants’ growth in high SO₂ showed a significant decrease in LMA compared with the control (with no SO₂).When grown in a highCO₂, lowO₂, and highSO₂ treatment,most plants continued to showa decrease inLMA compared with the control but an increase comparedwith the high SO₂ treatment with ambient CO₂ and O₂. Conclusions. Thesefindings suggest that exposure to SO₂ significantly decreasesLMA, potentially reducing preservation potential in the fossil record. Exposure to combined SO₂ and high CO₂ reduces this effect, but this may also obscure the effects of SO₂, leading to interpretations that ecosystem instability is primarily driven by increasing CO₂, which may not be the case.