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Climate change, antibiotics may threaten soil

Researchers say livestock antibiotic residues can degrade microbe activity when combined with rising temperatures.

Photo by Rockin'Rita

Higher temperatures brought on by climate change in many regions can disrupt soil microbe effectiveness, recent research shows.

A study by researchers at the Cary Institute of Ecosystem Studies in Millbrook, New York, has shown that when rising temperatures combine with antibiotic residues expelled by livestock, it degrades soil microbe efficiency, soil resilience to future stress, and its ability to trap carbon.

“Our lab group is interested in understanding how to manage our soils to maintain productivity,” said Jane Lucas, community ecologist. “We have historically done a lot of work looking at how antibiotic introductions shape soil microbiomes and influence rates of antibiotic resistance but with this project we were curious to see if temperature controlled these responses. We believe this is an important area to explore because many environments are experiencing warmer temperatures and antibiotic introductions.”

The study focused on monensin, a common antibiotic used on cattle farms.

The team used prairie soil samples from preserved land in northern Idaho that had not been grazed by livestock. Soil samples were treated with either a high dose, low dose, or no dose of the antibiotic, and heated at three different temperatures (15 C, 20 C, and 30 C) to represent seasonal variations. During each process, the researchers monitored soil respiration, acidity, microbial community composition and function, carbon and nitrogen cycling, and interactions among microbes.

“What we found was that the combined effects of temperature and antibiotic introductions had a big influence on the microbiome of our soils,” said Lucas. “While both antibiotics and rising temperatures are capable of shifting the microbiome, when they occur together, the bacterial taxa that are able to handle these two stressors is much less than those that can handle individual stressors.”

She said they saw major changes in microbe communities. Rising temperature exacerbated antibiotic effects with distinct microbial communities emerging at each temperature tested. They saw reduced diversity and fewer micro-organisms overall, changes that could diminish the soil’s resilience.

They also found that some of the effects of antibiotics only occurred at certain temperatures. The ratio of carbon to nitrogen decreased in antibiotic soils but only at 30 C. She said this demonstrated that some influences of stress may be context dependent. The change in carbon in relation to nitrogen was not necessarily good or bad, but it showed that the nutrient levels in the soils can change, with implications on how soils are managed and how they store carbon.

While types of fungi did not dramatically change when antibiotics were added, the community of fungi was much less diverse at 30 C than at the lower test temperatures.

One important result from the testing was that soils exposed to antibiotics had a higher mass specific respiration, a metric that shows soil efficiency. A higher metric, though, means soil communities are less efficient and antibiotics are making soils work harder for the same environmental outcome. This results in less carbon being converted into a stable organic form to be trapped in the soil. Instead, more is released into the atmosphere.

“In our initial findings, it looks as though soil microbiomes are often able to recover over a month after experiencing antibiotic introductions,” she said. “However, we are seeing that, when soils experience multiple stressors, their ability to recover is hindered and often slowed.”

It is likely producers could change the types of antibiotics being used and the timing of their introductions to protect soils and maintain the microbiomes.

Lucas added that any changes to the microbe community are not entirely negative.

While it is desirable to sequester carbon in the soil, soils have a baseline amount of carbon to start with and they can only hold so much. Climate change can complicate this.

“When soils warm up, microbial activity typically increases,” she said. “Soil microbes breathe out CO2 when they are active. As the climate continues to warm, we anticipate that soils will increase their baseline CO2 emissions. If soils are already inefficient, they are likely to emit even more CO2. This can mean that carbon is cycling rapidly in these systems and may not be stored at the levels we need.”

The United Nations Food and Agriculture Organization estimates that about 30 percent of all soils are degraded and 65 percent of soils are considered unhealthy. Managing these soils will take more time and money to keep them productive.

“It takes on average 200 to 400 years to grow one centimetre of soil but currently we are losing our topsoil 10 to 50 times faster than we are growing it,” said Lucas. “I have found that many land managers are very concerned about the changing conditions of their farms and we are seeing a lot of interest in managing for soil health.”

She said the onus shouldn’t all be on farmers to solve the big issues. It should be a co-ordinated effort by the public, policy makers, science, and stake holders to encourage sustainable agricultural systems and find ways to mitigate climate change.

In addition, farmers are fully aware of the potential issues when providing continuous antibiotics to their livestock, especially as it relates to the threat of antibiotic resistance and implications for human health.

“We also know that many farmers are aware of a growing consumer demand for antibiotic free food products,” she said. “This can be troublesome as it is common for animals to get sick. But deciding not to treat them is not a preferable choice.”

Going forward, one of the research goals is to follow up with more studies on crop growth and soil functions to see how they are influenced by different microbial communities. In addition, the research team plans to look at how antibiotic introductions influence antibiotic resistance in the soils and whether there is a potential influence on the health of animals and humans.

The team has also created a long-term field project called Stressed Out Soils. It involves treating soils with five different stressors including warming, simulated drought, antibacterials, antifungals or insecticides.

“Plots will receive different combinations of these with some receiving just one and others getting all five and everything in between,” Lucas said. “We hope this work will help inform land managers on what to expect in terms of soil nutrients and microbial communities in the face of climate change. We are also completing a nationwide survey of antibiotic resistance in soils.”

The research was published in the journal Soil Biology and Biochemistry.