The Universe Beneath Our Feet

When one tugs at a single thing in nature, he finds it attached to the rest of the world”

-John Muir

We often wonder of the world beyond our skies, heavenly bodies and extra terrestrial life; but we seldom stop and think of the bountiful universe beneath our feet. We have this universe to thank, for the food we eat, the clean air we breathe, quite literally for our very existence. Along with organic matter, decaying material and inorganic components of the soil, are present billions of lively microbes that are responsible for the continuos replenishment of our soils.

These microscopic beings strike a balance between certain harmful organisms and a plethora of beneficial organisms. The beneficial organisms play different roles in creating a conducive environment which directly and indirectly supports plant growth against abiotic and biotic stresses. Evolution has created such great biodiversity amongst these microbes, that they create a complex network complete with intercellular signaling.

The good bacteria often play the role of plant probiotics. They maintain the health of plants (by suppressing pathogens) and improve the organic content of the soil. Because of their intimate association (example endophytes), they play a critical role in nutrient uptake and plant metabolism . To sum up, plant probiotics can play an instrumental role in growth, plant yield and defense.

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Plant probiotics can be found:

  1. In the plant rhizosphere (within the soil, within and on roots)

  2. In the plant phyllosphere (within and on leaves)

Many factors affect the population of microbes present in any given soil. This is why, it is said that literally no two handfuls of soil can physically, chemically and biologically be the same. The Earth is divided into various zones depending upon the geographic location of these zones and their placement on the Earth in relation to its proximity to the sun. Depending on this, the soils of each region have developed special features that vary extensively. Soil composition, structure, water retention capacity, organic content all play a role in deciding the microbial diversity. Other abiotic factors include nutrient availability, water supply, temperature, incident sun light, application of chemicals (fertilizers, pesticides, herbicides, insecticides), release of effluents / toxic matter into the soil etc. Insect activity, presence of organic matter, inhabiting animals, plants all highly influence the fertility of the soil. Some plant species have rhizosphere that typically attract a host of plant growth promoting organisms in the soil.

Microbes fall under the basic three categories: bacteria, fungi and actinomycetes. Depending on what kind they are, their role in the plant rhizosphere/phyllosphere varies. All three play cruicial and distinctive roles in soil conditioning through the product. Actinomycetes and fungi actively produce metabolites that keep pathogenic organisms in control. These organisms also influence hormone production in plants, thereby directly influencing their physiology and yield ( in case of crops).

Microbes can also trigger a phenomenon in plants known as induced systemic resistance (ISR) that activate the plants’ defense mechanisms in response to infection by a pathogenic agent. The plants become less prones to onslaught of soil borne or air borne infections. They build a lasting immunity in plants.

Physical stresses include extremes of extremely high or extremely low temperature, high light intensity, flooding, drought, the presence of toxic metals and environmental organic contaminants, radiation, wounding, insect predation, nematodes, high natural salinity, excessive fertigation induced salinity. These stresses may be present in lethal or near lethal amounts due to which the plant may or may not able to adjust its metabolism to overcome the stress. Plant growth promoting bacteria may directly or indirectly play a role in helping the plant overcome these stresses. They may produce chemicals that shield the rhizosphere from such stresses or may produce hormones to help the plant grow when it is unable to produce them on its own.

A complete understanding of how these organisms work and why they exist has not been achieved. Their existence and ours are interwoven, On account of Earth Day,let us pledge to appreciate and preserve this gift to all living kind.

Nature is not a place to visit. It is home.”

Gary Snyder

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