Loss of biodiversity limits toxin degradation

"Caution and long term evaluation is required if we are to continue to rely on soil as a buffer and filter for the food chain and our waterways.

You might not think of microbes when you consider biodiversity, but it turns out that even a moderate loss of less than 5% of soil microbes may compromise some key ecosystem functions and could lead to lower degradation of toxins in the environment. That is the finding of new research carried out in Scotland by an international consortium including the James Hutton Institute.

A study published in Environmental Microbiology, the journal of the Society for Applied Microbiology, reports that without a rich diversity of soil bacteria, specialised functions such as the removal of pesticide residues are not as effective.

Dr Brajesh Singh of the University of Western Sydney, who led the work, said: "If the ability of the ecosystem to remove toxins from the environment is reduced, there will be higher toxicity risks in the environment and for non-target organisms, including humans, from agricultural chemicals.

“It is likely that these contaminants will remain at higher levels in surface and underground water, as well. It is vital to gain a better understanding of the extent to which soil bacteria are involved in the removal of contaminants."

The reasons for, and extent of, the decline in microbial diversity in agricultural soils is likely to be complex. The team has looked specifically at long-term heavy metal pollution where metals such as cadmium, zinc, and copper build up in the environment, usually as a result of industrial use.

Another source is from digested sewage sludge, which is spread in agriculture fields to supply nutrients to crops and improve soil fertility; the sludge has historically contained some heavy metals, which can become concentrated in the soil.

Although the concentration of heavy metal used this study was higher than the current EU limit, this study has confirmed that long-term exposure to such contaminants does reduce the diversity of bacteria in the soil.

Professor Colin Campbell, Director of Science Excellence at the James Hutton Institute and co-author of the study, said: “We must maintain the precautionary approach currently adopted for the long term recycling of any materials that contain heavy metals and we need to appreciate and understand the effects of heavy metals on soil micro-organisms in much more detail.

“As fertiliser and energy costs rise long term food security will rely on recycling recovered nutrients from sludge and other organic materials which can be very useful for maintaining soil fertility. Caution and long term evaluation is required if we are to continue to rely on soil as a buffer and filter for the food chain and our waterways.”

With the global population set to reach nine billion by 2050, we face a challenge to feed an extra two billion mouths using the same resources that we have at present. Crop losses to pests and disease account for a large percentage of under-production and so giving up pesticides will be difficult. Similarly, the use of sludge as a fertiliser is likely to become more prevalent. Research like this allows us to understand how to use important agrichemicals and waste products in a sustainable way and so will contribute to future food and environmental security.

The research was carried out by a team of scientists from the universities of Western Sydney, Glasgow, Copenhagen and Oklahoma, as well as the James Hutton Institute, Scotland’s Rural College and the Swedish Agricultural Sciences University.  

Notes to editors:

Paper: Loss of microbial diversity in soils is coincident with reductions in some specialised functions. Brajesh K. Singh, Christopher Quince, Catriona A. Macdonald, Amit Khachane, Nadine Thomas, Waleed Abu Al-Soud, Søren J. Sørensen, Zhili He, Duncan White, Alex Sinclair, Bill Crooks, Jizhong Zhou and Colin D. Campbell.