Scientists find grass yield, carbon storage not affected by creepy-crawlies in the soil

New results from experiments at a unique ecology facility show that plant communities are dramatically altered by changes to the type of animal species living among their roots, but that key ecosystem measurements such as overall agricultural yield or the amount of soil carbon stored are unaffected.

According to the results of a three year study into the processes of experimental grassland ecosystems published in the journal Science today, changes to the makeup of soil communities from small to large animal body sizes -ranging from bacteria and fungi to worms and beetles – have no significant effect on the overall yield of the plant life above, nor on the overall amount of carbon stored away in the soil.

The researchers from England, Wales, Scotland, Germany and Finland say that the results of their experiment send an important message about the ability of natural ecosystems to cope with human impacts, such as changes to the composition of soil communities, but caution that further long-term work is needed to confirm their findings.

“The study suggests that if you mess about with soil communities, say from the impacts of global change, you may alter the way the systems work but this has no major consequence in terms of the system’s outputs, for example the amount of grass produced,” says Dr Mark Bradford, lead author of the study based at the Natural Environment Research Council (NERC) Centre for Population Biology, Imperial College London.

“However, further studies may reveal that these changes have an impact over a longer time scale and our current investigations suggest that this could well be the case,” he adds.

The findings are based on work into the effects of global change on soil biodiversity done at the UK’s unique Ecotron research facility at the NERC Centre for Population Biology. The Ecotron consists of 16 sealed walk-in chambers with computer-controlled climatic conditions.

Each chamber housed a mini grassland ecosystem one metre square taken from Sourhope, a grazed upland grassland habitat in Scotland.

Over seven months researchers removed soil animals and then artificially reconstructed the grasslands with animals that differed in their body sizes – treatments contained small, medium or large soil fauna.

The experiment ran for nine months, during which seasonal conditions were set to mimic June/July temperatures in Scotland – akin to a continuous growing season.

The researchers had their expectations, based on previous, simpler experiments, turned on their heads when they came to examine the results.

They had predicted that the larger fauna communities would lead to changes in the composition of the plant community and a rise in the yield, or Net Primary Productivity, because of the previously reported positive effects of these fauna on soil fertility and plant growth. They also expected to see an increase in the amount of carbon stored in the system, or Net Ecosystem Productivity.

In fact they found neither; the different animal soil communities did not change overall vital ecosystems services such as the amount of carbon stored in the soil or the overall yield.

To explain their results, they suggest that both positive and negative effects of the fauna in the soil act to cancel each other out, causing no net ecosystem effects.

The Natural Environment Research Council provides core funding to the Centre for Population Biology as well as funding for this research under its Soil Biodiversity Programme.