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Drought-quenching bacteria the future of farming?

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NAU doctoral candidate Rachel Rubin teamed up with artist Victor Leshyk to illustrate rhizobacteria as a “prescription” for drought.

Though we cannot see them with the naked eye, bacteria are virtually everywhere. A single teaspoon of soil contains about one billion bacterial cells. From the barren valleys of Antarctica to the gassy corners of the human gut, bacteria are thriving and multiplying. But contrary to popular association, not all bacteria are harmful.

In fact, some bacteria can even help us meet global food demand while handing adverse effects of climate change.

In a recent study, NAU researchers investigated the microscopic world buried in earth’s soil. Led by doctoral student Rachel Rubin at the Center for Ecosystem Science and Society, they published findings that show how certain bacteria, called rhizobacteria, could help mitigate crop losses due to drought.

Rubin explained that the bacteria can be collected from arid regions where they grow naturally, and introduced to areas suffering from drought. This practice can have a positive impact on food security, water conservation, and sustainability.

The team found 20-40 percent increase in growth when a plant was introduced to rhizobacteria, and the effect was consistently stronger under drought.

“This is encouraging because it means that the places most vulnerable to climate change will benefit the most” Rubin shared.

In the next 30 years, global food demand is expected to double to keep up with a rapidly growing population. And it’s no secret that crops need water to survive.

While the global climate changes, the demand for water increases. Drought stress already reduces crop yield worldwide, and an increase in soil saltiness threatens more than half of the world’s farmable lands.

In the past, drought has been combated with improved irrigation methods. However, irrigation already accounts for over two-thirds of global water consumption and will not be enough to solve this problem alone.

Surprisingly enough, Rubin’s study shows that rhizobacteria promote plant growth even better under drought conditions.

To come to these conclusions, Rubin performed a meta-analysis. She combed through thousands of scientific papers related to rhizobacteria and drought. Ultimately, she chose 52 studies to compare, using the criteria that each study selected had to be conducted the same way.

Rubin then compiled and synthesized the experiments, reducing the data into a single study. Her examination included a diversity of bacterial and plant taxa, which all showed a universal benefit.

“This is the first study that has quantitatively shown that rhizobacteria can improve plant growth in drought” Rubin shared.

This study highlights the fascinating relationship between plants and the many species of bacteria that colonize in and around their roots.

“They’re a form of symbiosis called a mutualism, meaning a mutually beneficial relationship between plants and bacteria,” explained Rubin.

Plants provide sugars, carbohydrates, and a place to live for the rhizobacteria. In exchange, the bacteria help the plants forge for nutrients in the soil. Different species of bacteria vary in how they promote plant growth under drought. For example, some produce enzymes that slow wilting and others can create biofilms that help soils retain water.

Rhizobacteria grow on a variety of plants in a range of places, Rubin explained.

“It ranges from the tomato rhizospheres in Senegal, to ‘salty rice’ in Egypt; wild barley on Mt. Carmel, to Ponderosa Pine on Mt. Lemmon.”

Although rhizobacteria are co-evolved with their plant hosts, the researchers have not seen any negative effects of introducing them to a new host. Additionally, there is not a dominant functional group of plants that recruit rhizobacteria the best, Rubin explained. But future work may reveal which plant hosts to focus on.

However, rhizobacteria are far from an end-all solution.

“We still have a lot to learn in order to scale inoculants to the farm level, but it’s encouraging that research on rhizobacteria continues to grow,” said Rubin.

In the future, rhizobacteria could be used to augment existing soil conservation practices, including no-till farming and intercropping.

For now, Rubin intends to take this research home and apply her studies to native Arizona grasses.

Rachel Rubin is a Ph.D. candidate at Northern Arizona University’s Center for Ecosystem Science and Society. She received a BS in Wildlife Ecology and Conservation from the University of Florida. Her mentor is Dr. Bruce Hungate.

Taylor Hartman is this year's NASA-NAU Space Grant science-writing intern at the Arizona Daily Sun.


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