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Split personality of soil bacteria

Study unlocks surprising behavior of soil bacteria

Newly sequenced genomes of soil bacteria have raised questions about how differing land management affects the organisms’ behavior.

UK scientists found one strain locked nitrogen in the soil, while another released a potent greenhouse gas.

The findings came to light after the researchers sequenced Bradyrhizobium, one of the most active and abundant groups of soil bacteria.

The findings were published recently in the journal Scientific Reports.

The team from the University of Reading and Rothamsted Research were the first to sequence the genome of Bradyrhizobium from European soils, allowing the scientists to compare strains of the bacteria from different parts of the world.

They collect strains of bacteria from various soils in a long-term experiment at Rothamsted Research, from plots that had been maintained as grassland or ploughed bare soil for the past six decades.

Bradyrhizobium growing on agar plates (Image: Rothamsted Research)
Researchers were surprised to find the bacteria, closely associated with plant growth, so abundant in bare soil

Lead author Frances Jones, who carried out the study as part of her PhD study, explained: “Bradyrhizobium is usually known for its close relationship with plants and so the fact that it is present in bare soil is exciting.

Prof Penny Hirsch, who leads the soil microbial ecology group at Rothamsted Research, added: “Discovering that one of the most abundant groups of bacteria in soil is potentially responsible for major nitrogen losses, and showing how different treatments affect this group in the long term, is an important step towards managing the soil to minimise fertilizer use whilst maintaining crop yields.”

Close up dusty hand (Image: BBC)
A growing body of research considers the symbiotic relationship between plants and soil

International attention was focused on the ground beneath our feet during 2015, which was designated the UN International Year of Soil.

Described as one of the most complex biological materials on the planet, a handful can contain billions of micro-organisms. It is estimated that just a centimeter of topsoil can take about 1,000 years to form.

ArcheWild note: “It is true that the structure, chemical composition, and microbial populations represented in the top 0.25″ of soil represents 1000’s of years of development.  These topsoil attributes, we believe, have a direct and profound influence on the types of plant species that are able to emerge, influenced by seed germination, drainage, and nutrient availability requirements.  Topsoil is highly unique and highly local, based on its parent material, bedrock influences, and historical use.  Much of the success of a native planting, whether it be a detention basin, a meadow, or a public park, depends on matching the topsoil, and subsoil, attributes to the needs of the desired plants.  Soil specifications is a major, perhaps the most important, component of any landscape design process.”

ArcheWild note: ” Core concept: There is no such thing as “topsoil.”  Engineering drawings and landscape architecture specifications are bereft of the necessary detail for a contractor to build a soil profile that satisfies the needs of the plantings they intend to use, for the long term.  Contact ArcheWild for assistance in writing a soil specification that will actually support a durable planting using the species that you intend to use on your project.”

Recognizing the importance of healthy soil for farming, the Scottish Environment Protection Agency (SEPA) requested the publication of advice of how to look after soil.

It is thought that 2.9 million tonnes of soil is eroded each year, and soil quality is diminished by poor practices.

SEPA principal policy officer Mark Aitken added: “The publication is also immensely useful because it highlights the importance of good soil structure in protecting and improving water quality, and also in helping to reduce flood risks.”

ArcheWild note: “Much of the benefit of a riparian restoration lies not in the ability of the plantings to ‘soak up rainwater’ but in the potential of the planting to improve the structure of the underlying soil, through a variety of mechanisms, such that rainwater infiltration is improved.  For example, just one square foot of 3″ of decomposed leaf litter is able to absorb more than one gallon of water without effluent.”

Rothamsted Research’s Frances Jones said that there was a growing body of scientific work that considered the role of soil.

“There seems to be more and more studies coming in that are looking at both plants and below-ground function rather than treating them as two separate things,” she told BBC News.

“It is becoming more common that people are looking at this interaction rather than separate environments.”

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