An international team of scientists led by researchers from the University of Leeds has revealed in new research that tropical soils are more sensitive to a warmer climate than previously thought.
The new work published in Nature Microbiology suggests that the number of microbial species in tropical soils could reduce as a result of global warming. A decline in species would pose a threat to the biodiversity of rainforests. More carbon could also be emitted into the atmosphere as a result.
Tropical soils hold around a third of carbon stored in earth’s soils. Researchers say they support about two-thirds of the global plant biomass.
Soil microbes play a critical role in the maintenance of tropical forest ecosystems, as per scientists. They help break down dead organic matter, using the constituent carbon or releasing it as CO2 into the environment. A decline in microbial diversity is, therefore, a thing of major concern.
Warming tropical soils
Going by climate model estimates, the tropics could become two to five degrees Celsius warmer by the end of this century. Minimal research has been carried out up till now on what effects this could have on microbes in tropical soils.
The team in the current research, therefore, set out to explore what could result if tropical soils were exposed to the degrees of warming forecasted by climate models.
These researchers experimented on Panama’s Barro Colorado Island to estimate the possible impact. With the aid of an underground heating system, they warmed five plots in an area of lowland tropical forest to predicted warming levels. These experimental plots were compared with unheated “natural” plots.
What the team observed two years after the heating system was set up challenges what experts currently think could be the impact of global warming on tropical soils.
“This research is prompting us to think differently about the way a warmer climate may affect tropical soils, which support some of the world’s richest biodiversity and are a globally important store of carbon,” said lead author Dr. Andrew Nottingham, a forest ecologist at the University of Leeds.
Dr. Nottingham and his fellow researchers made two major findings that were surprising in this study.
First, the team found that a lot of the major fungal and bacterial species present in the unheated plots were missing in the heated plots. At the same time, they also observed that certain bacteria and fungi were present in the heated plots but not in the unheated control plots.
This finding challenges a long-held theory that an increase in soil temperatures would cause bacterial diversity to rise.
“If the results that we have seen in just two years are representative of what will occur in global tropical soils, then there will be a major negative impact on the rich ecosystems they support,” Dr. Nottingham said.
The researchers wondered if the microbes that were absent in the heated plots were critical to soil functioning. This is because of the correlation between soil microbial diversity and soil health.
Observed changes in biodiversity could have serious implications on plants. What is happening under the ground will likely be seen above it in terms of visible vegetation.
The second unexpected finding was a rapid increase in CO2 emissions. Researchers had found in experiments that were not done in the tropics that CO2 emissions into the environment rise as temperatures surge. The rate of acceleration in emissions observed in the heated soil in this study was three times more than what scientists had previously predicted.
Only a little change in the rate of CO2 emissions could have a huge impact on climate change, as per scientists. The higher rate of acceleration is, therefore, more worrying.
Dr. Nottingham described the implications of these results as alarming. This research underlines the urgent need for efforts at protecting “these biodiverse and carbon-rich ecosystems and to tightly limit current warming,” he stated.
The researchers noted that there were still many unanswered questions. They include the possible response of plants to above-ground warming and how the observed changes in the heated plots would apply to global ecosystems. These questions will have to be addressed in future research.