Effects of Sulfur Dioxide Exposure on Leaf Mass per Area of Selected Gymnosperms and Implications for Interpreting the Plant Fossil Record

Abstract

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 high CO2, low O-2, and high SO2 treatment, most plants continued to show a decrease in LMA compared with the control but an increase compared with the high SO2 treatment with ambient CO2 and O-2. Conclusions. These findings suggest that exposure to SO2 significantly decreases LMA, 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.