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Killer gas or plant grower
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| Hydrogen sulfide emissions outside the coast of Namibia 2012. Source: NASA |
A poison or a saviour?
Hydrogen sulfide (H2S) is a colorless gas that is heavier than air, smells like rotten-eggs and very poisonous to most organisms (including humans). It results from bacterial breakdown of organic matter in the absence of oxygen, a process known as anaerobic digestion. H2S is very toxic to local marine organisms, fish die in low-oxygen (anoxic) water. The production of H2S is believed to have been one of the contributing causes to pre-historic mass extinctions (Ward, 2007). The theory is that global warming (CO2 increase in the atmosphere) lead to a slowdown in ocean currents as the temperature gradient between the poles and equator diminished, which in turn led to anoxic conditions that produced massive quantities of hydrogen sulfide, killing off vast amounts of plant and animal life. However, last year scientists found that dissolved H2S, in very small doses, can also have a growth effect on plants (Dooley et al. 2013). If correct, we may have found a way to enhance yields without using petroleum, which would be a major breakthrough for humanity.
Biological effects of H2S
The biological effects of H2S have received increasing attention during the last decade. Not only as a considered kill mechanisms during past mass extinctions but also as an important signalling molecule in organisms. While high levels of gaseous H2S kills plants, extremely low levels of liquid H2S seem to trigger a growth spurt. The origin of these dual activities remains unknown but scientists suggest it might be remnants of biological responses by life evolving in highly anoxic environments of earlier times in Earth’s history. Studies into the effects of sulfide compounds on plants are still few and most have focused on the lethal effects. It is known that H2S causes inhibition of photosynthesis at high concentrations but less is known about what happens at lower exposure.
Increasing yields
A group of scientists at University of Washington reported in 2013 that by exposing plants roots or seeds to very low concentrations of dissolved hydrogen sulfide at any stage of life caused significant increases in biomass, including higher fruit yield. The study found that germination success and seedling size increased in bean, corn, wheat and pea seeds. They also found that time to germination in seeds treated with H2S was significantly less than values observed in untreated seeds (see figure below)
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| Space Wheat seed (treated H2S seeds in the bottom) photo series taken over 119 hours |
Enhanced growth rate continued for seven days after a single exposure, followed by a return to the slower growth unless re-exposed. The H2S exposed plants reacted with cellular divisions, increasing the absolute number of chloroplasts per area. One hypothesis is that H2S does not increase growth rates as a byproduct of the addition of sulfur as a “fertilizer”, as seen through the addition of phosphates or nitrates, but actually impacts cellular replication and photosynthesis. This rapid growth behaviour may have been selected for as toxicity decreases with larger plant size. While this research is recent and further studies are needed, this could have large implications for agriculture and biofuels.
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