While adapting to hotter temperatures, bacteria tend to accelerate their respiration rate and emit more carbon, possibly speeding up climate change.
By emitting more carbon with the increase in global temperatures, bacteria and associated organisms known as archaea could increase climate warming at a rate faster than that suggested by existing models.
The new research, published recently in Nature Communications by researchers from Imperial College London, could help develop more accurate models of future climate warming.
Bacteria and archaea, together referred to as prokaryotes, are found on all continents and constitute about half of the biomass worldwide—the overall weight of all organisms on Earth.
A majority of the prokaryotes use energy and discharge carbon dioxide (CO2) during respiration—similar to what humans do when they breathe out. The amount of CO2 discharged during a particular time period relies on the respiration rate of the prokaryotes, which can vary based on temperature.
However, the precise relationship between respiration rate, temperature, and carbon output has been unclear. By gathering a database of variations in the respiration rate of 482 prokaryotes based on temperature, scientists have learned the majority will intensify their carbon output in reaction to higher temperatures to a greater extent than formerly thought.
“Double Whammy” Effect
In the short term, on a scale of days to hours, individual prokaryotes will increase their metabolism and produce more carbon dioxide. However, there is still a maximum temperature at which their metabolism becomes inefficient. In the longer term, over years, these prokaryote communities will evolve to be more efficient at higher temperatures, allowing them to further increase their metabolism and their carbon output.
Dr Samraat Pawar, Lead Researcher, Department of Life Sciences, Imperial College London
Dr Pawar added, “Rising temperatures, therefore, cause a ‘double whammy’ effect on many prokaryote communities, allowing them to function more efficiently in both the short and long term, and creating an even larger contribution to global carbon and resulting temperatures.”
Prokaryotes from all Environments
The scientists collected prokaryote responses to temperature variations from around the world and in all various conditions—from salty Antarctic lakes below 0 °C to thermal pools above 120 °C.
They learned that prokaryotes that typically function in a medium temperature range—below 45 °C—exhibit a strong response to varying temperature, increasing their respiration in the short term (days to weeks) as well as the long term (months to years).
Prokaryotes that function in higher temperature ranges—above 45 °C—did not exhibit such a response. However, since they function at such high temperatures to start with, they are not likely to be influenced by climate change.
The short-term responses of medium-temperature prokaryotes to warming were greater than those observed for eukaryotes—organisms with more complex cells, including all fungi, plants, and animals.
Departing from the “Global Average”
The researchers developed a mathematical model that forecasts how these variations in respiration rate would impact the carbon output of prokaryote communities. This showed that short- and long-term variations to respiration rate would combine to form a larger-than-predicted rise in carbon output, which is presently unaccounted for in climate and ecosystem models.
Most climate models assume that all organisms’ respiration rates respond to temperature in the same way, but our study shows that bacteria and archaea are likely to depart from the ‘global average’. Given that these micro-organisms are likely to be significant contributors to total respiration and carbon output in many ecosystems, it’s important for climate models to take into account their higher sensitivity to temperature change at both short and long timescales.
Thomas Smith, Study Lead Author and PhD Student, Department of Life Sciences, Imperial College London
Thomas Smith continued, “Importantly for future climate predictions, we would also like to know how the numbers of prokaryotes, and their abundance within local ecosystems, might change with increasing temperatures.”