Evolutionary legacy response observed in algae and bryophytes following hydrogen sulfide administration

<div><p>The study presented here examined the effects of administering hydrogen sulfide (H₂S) to several ancient extant plant species to determine the organisms’ response to stress. Even though sulfur is an essential macronutrient required for growth and productivity, there are toxic compounds of this element that exert detrimental effects and produce physiological stress. It is speculated that the accumulation of H₂S, a lethal gas, may have been a major contributing factor in past mass extinction events, where the environment was fairly anoxic with fluctuating temperatures. The potential of this toxic compound to exist as an environmental stressor suggests that certain organisms may have adapted to survive these periods of mass extinctions. It is hypothesized that due to the abundant presence of H₂S in the past, ancient land plants may have an adaptive advantage that allowed them to survive and thrive. In this study, species of bryophytes and algae were exposed to specific concentrations of aqueous H₂S over a seven-day period and measured their photosynthetic capacity at timed intervals using a FluorCam. Studying the effects of this toxic gas on ancient plants is imperative to our understanding of sulfur's varying biological roles, and provides insight on the evolutionary phenotypic variations amongst plants and stress responses in order to survive mass extinctions. Results indicate that <i>Hypnum</i>, <i>Chlamydomonas</i>, and <i>Charophyta</i> are all able to tolerate significant quantities of H₂S and show resilience through increased photosynthetic capacity over a period of exposure, indicating a genetic and phenotypic legacy response.</p>