Biological Nitrogen Fixation By: Stephen C. Wagner

Soil Bacteria, A Community Supporting Plant Health

Plants have their own microbiome, just like humans.  Humans have microbes on their skin and inside their body: Probiotics are microbes that humans encourage within their digestive track. Plants have a similar system, where microorganisms, including bacteria, live on and in plant roots.  Many of these species, called Plant Growth Promoting Rhizobacteria  (a.k.a. PGPRs), are beneficial to plants. 

PGPRs help plants cope with environmental stress, much like our own gut microbial biome. Additionally, Plant Growth Promoting Rhizobacteria feed plants, literally helping them grow.

A plant’s bacterial besties

Nitrogen-fixing Bacteria, part of the Soil Microbe Biome
Nodules on roots, created by Nitrogen-fixing Rhizobacteria

Probably the most well-known Plant Growth Promoting Rhizobacteria are the Nitrogen Fixing Bacteria, Frankia and rhizobia. These  live inside special chambers plants set up within their roots.  In this protected space away from oxygen, the bacterial partners transform nitrogen from the air, which plants can’t use directly, into molecular forms the plant can.  But this is just the tip of the iceberg when it comes to beneficial bacteria-plant relationships.  Other types of bacteria play a role in helping plants absorb phosphorous and iron, critical nutrients that are often present in soil, but in a form plants can’t access. 

Plants uptake nutrients dissolved in the water that enters their roots.  Both phosphorous and iron tend to combine with other elements to form compounds that don’t easily dissolve in water.  Certain PGPRs release acids that make phosphorous more soluble in the water around plant roots, right where it’s needed.  Other Plant Growth Promoting Rhizobacteria release special molecules called siderophores that act like shuttles to go out and “fetch” iron for the plant.

Besides providing plants with important nutrients they need, PGPRs protect plants from stresses that would otherwise inhibit their growth.  Stress can be caused by drought, heat or cold, or accumulation of salts.  Studies have shown how some bacterial partners can alter the gene expression of plants to help them navigate sudden environmental changes.

One result might be to increase antioxidants in the plant to help them weather the stress.  It might result in stockpiling sugars that act like a kind of antifreeze to guard against cold.  Plant cells may become better at reducing sodium accumulation in roots so they can tolerate this salt better.  A stressful environment can also be caused by living organisms, like pathogenic bacteria or fungi.  Some PGPRs secrete antibiotics to combat the pathogens directly.  Others indirectly subdue pathogens by out-competing them for nutrients and space. 

Bacteria, especially nitrogen fixing
 bacteria, play a key role in the 
complete soil food web
Bacteria, especially nitrogen fixing
bacteria, play a key role in the
complete soil microbe biome

PGPRs can even literally signal plants to grow bigger by making and releasing hormones plants respond to.  Molecules called auxins, cytokinins, and gibberellins signal to the plant to increase its root and shoot growth – good news for crop yields.

PGPRs are 21st century farming technology

Chemicals were the tool of 20th century farming, but biology is for the 21st century.  Fertilizers, pesticides and hormones can be applied to crops to do many of the functions above.  Unfortunately, chemical runoff is both a waste of resources and environmentally polluting. 

By using microorganisms, nutrients already present in the air and soil become useful to plants.  The nutrients are provided at a level and a rate compatible with the plant’s needs, so these resources stay in the soil system instead of leaching away.  “Restoring the native micro biome is imperative to building the plant’s immune system which in turn reduces a need for pesticide applications,” says Katharine Hinson, SymSoil’s President of Science. 

Another benefit of using biological diversity is that it can rapidly adapt to new situations – something that could be important for agricultural systems in the context of climate change.  A plant, “rooted to the spot” during its lifespan, heavily relies on its bacterial (and fungal) allies.  It may even actively recruit allies with specific talents useful in a particular situation.  But to develop these useful partnerships, the right microorganisms need to be present in the soil.

SymSoil delivers a robust bacterial community to the soil

Healthy soils contain up to a billion of bacteria in just a single teaspoon.  Plants attract their beneficial bacterial partners by releasing molecules called exudates out from their roots and into the soil.  The greater the diversity of bacteria in the soil, the more diverse PGPRs these plants can attract that make the plant more adaptable.  Maintaining crop diversity is one way to support bacterial diversity; SymSoil® V50 is another.  SymSoil® V50 contains a blend of both Robust Compost (RC) and Fungal Infused Biochar (FIB).  SymSoil® RC brings a diversity of bacteria, in addition to six other forms of life, while SymSoil FIB contains biochar, a medium that enhances delivery of the microorganisms to the soil.

About SymSoil Inc

SymSoil is a leader in development of biological soil amendments for agriculture that restores the microbes that provide the right food to the plant roots, improving plant health, and making food more nutrient dense and flavorful, the way nature intended. SymSoil has products and services for growers using regenerative agriculture methodologies which improve profitability. Its flagship product, SymSoil® RC (Robust Compost) is a complex community of soil microbes, which includes in excess of 1,000 species, covering broad biodiversity of bacteria, fungi, amoebae, and other protozoa, beneficial nematodes and microarthropods. SymSoil was named one of 2019’s AgTech Companies to Watch. Accredited Investors can learn more about SymSoil as an impact investment here. 

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