The Role Of The Soil Microbiome In Nutrient Cycling

Microbes communicate and work together to guarantee nutrient availability translating into a self-sustainable agroecosystem.

FREMONT, CA: With alarmingly increasing soil degradation globally, it is imperative to acknowledge the role soil microbiome performs in restoring soil functionality and suitability for sustainable agriculture.

Soil biodiversity plays a major role in sustaining most life forms. Microbiome, a term employed to define a community of all tiny organisms invisible to the bare eye, rationalizes about 60%- 80% of soil biological operations like biogeochemical cycles of soil nutrients. Microbes communicate and work together to guarantee nutrient availability translating into a self-sustainable agroecosystem.

With recent advancements in molecular techniques, scientists are initiating to decipher the diversity and role of the soil microbiome.

How do they do it?: The soil food web plays a critical role in the cycle of nutrients.

Different types of microorganisms and their respective roles in improving soil health.

 • Cleaners: Microorganisms under this category are intricated in decomposing soil organic matter. They can be employed in the bioprocessing of soil rendered infertile due to synthetic fertilizers;

 • Fixers: These microorganisms can turn atmospheric Nitrogen into a more useful form to be taken up by plants and other microorganisms;

 • Extractors: These microorganisms – like Mycorrhizae – are very tiny. They pierce small spaces that plant roots cannot pass over or reach and extract nutrients such as calcium and phosphorus, making them bioavailable to plants.

The cleaners: When dead and disintegrating matter like animal and crop residues, leaf litter, wood chips, and living soil microorganisms are united, they make up the Soil organic matter (SOM).

Decomposer microorganisms prey on the SOM by secreting enzymes that disintegrate complex organic matter, such as cellulose and chitin, into soluble compounds that plants can easily absorb.

Nutrients such as Carbon, Nitrogen, and potassium are released back into the soil, an important step in recycling soil nutrients. During this process, microbes employ some Carbon molecules and ‘breathe out’ carbon dioxide, finishing the carbon cycle.

Some organic compounds generated during the decomposition bind together (aggregates) with the remaining carbon molecules. Soil aggregation is important for water retention and air circulation. The leftover SOM that does not undergo decomposition forms the soil organic carbon (SOC), pictured as the dark-colored appearance of the soil.

When SOC residue is in the soil for a long duration, it binds with other nutrients and becomes stable, forming humus which numerous farmers associate with soil fertility. However, the amount of soil organic carbon stored depends on factors ranging from soil type to land management practices.

The Fixers: Plants “talk” to soil microbes by emitting molecular signals. Plant microbial interaction start in the rhizosphere. This is an area where plant roots are surrounded by soil famous for hosting the majority of soil microorganisms.

Some plants release host-specific signals (similar to speaking the same language), attracting specific microorganisms to plant roots. At the same time, other plants exudate signals that attract a wide range of microorganisms. As a result, microbes either attach themselves to the roots or enter the plant root cells.

A benefit of beneficial bacteria on the plant root surface is that they form biofilm. This slimy coating layer protects the host plants from environmental stressors like drought and disease-causing microorganisms in biocontrol. In reply, they obtain energy from glucose derived from the photosynthetic process of plants.

Here comes the natural fertilizer!: The atmosphere stores nearly 78% of Nitrogen in gaseous form. However, this gaseous Nitrogen cannot be absorbed directly by plants due to its strong bonds. Instead, it takes the intervention of specific soil microorganisms to fix Nitrogen in the soil.

Nitrogen-fixing bacteria can be free-living and act independently in the soil. Others form a symbiotic relationship. For instance, Rhizobium sp. penetrate the root of leguminous plants stimulating plant cells to undergo cell division resulting in forming of nodules. These are apparent structures found on the rooting of legumes like clover, cowpea, beans, and alfalfa. These Nitrogen-fixing bacteria grab Nitrogen gas from the atmosphere and convert it to ammonium, making it available for plants and other soil microorganisms.

Exhausters: These microorganisms incorporate motile-free living bacteria into mycorrhizae fungi, bringing nutrients to the plant. They can rise in spaces where nutrients and water have been kept in soil organic matter. Other roles include:

 • The growth of hyphal tips with weak spots on rocks initiates the breakdown of rocks, discharging nutrients such as Phosphorus, Calcium, and Potassium;

 • Decrease weed growth because of competition for nutrients;

 • Arbuscular mycorrhizal fungi (AMF) produce a substance called glomalin. This enhances soil fertility and prevents soil erosion;

 • Have a high-water retention ability to supply plants with water during dry periods.

Restore the soil microbiome

 • Create awareness of soil biodiversity;

 • Feed the soil with organic amendments like crop residues compost, Vermicompost, and Biochar;

 • Kickstart dissipated soil by applying a mixture of bacteria and fungi;

 • Offer shelter to microbes by planting cover crops;

 • Withstand agricultural practices that disrupt the soil microbial community.