Hydrogen sulfide, the pungent stuff often referred to as sewer gas, is a deadly substance implicated in several mass extinctions, including one at the end of the Permian period 251 million years ago that wiped out more than three-quarters of all species on Earth. But a study published in PLOS ONE shows that in low doses hydrogen sulfide could greatly enhance plant growth, leading to a sharp increase in global food supplies.
The researchers initially were out to examine the toxic effects of hydrogen sulfide on plants but mistakenly used only one-tenth the amount of the toxin intended. The results were so unbelievable that the researchers repeated the experiment, with the same results. At high concentrations—levels of 30–100 ppm (part per million) in water—hydrogen sulfide can be lethal to humans. At 1 ppm it emits a telltale rotten-egg smell. The researchers used a concentration of 1 ppb (part per billion) or less to water seeds of peas, beans, and wheat on a weekly basis. Treating the seeds less often reduced the effect, and watering more often typically killed them.
With wheat, all the seeds germinated in one to two days instead of four or five, and with peas and beans the typical 40% rate of germination rose to 60–70%. “They germinate faster and they produce roots and leaves faster. Basically what we’ve done is accelerate the entire plant process,” said Frederick Dooley, a University of Washington doctoral student in biology who led the research. In addition, crop yields nearly doubled.
Hydrogen sulfide, probably produced when sulfates in the oceans were decomposed by sulfur bacteria, is believed to have played a significant role in several extinction events. The rapid plant growth could be the result of genetic signaling passed down in the wake of mass extinctions. At high concentrations, hydrogen sulfide killed small plants very easily while larger plants had a better chance at survival, so it is likely that plants carry a defense mechanism that spurs their growth when they sense hydrogen sulfide.
Dooley recently has applied hydrogen sulfide treatment to corn, carrots, and soybeans with results that appear to be similar to earlier tests. But it is likely to be some time before he, and the general public, are comfortable with the level of testing to make sure there are no unforeseen consequences of treating food crops with hydrogen sulfide.
The most significant near-term promise, he believes, is in growing algae and other stock for biofuels.