Plants have evolved along with soil microbes for hundreds of millions of years. When bacteria colonized the Earth and changed the atmosphere more than three billion years ago, they created conditions that allowed the evolution of soil fungi (around 900 million years ago). You can check about plant growth promoting bacteria -growing cannabis indoors through an online search.
Together, bacteria and fungi form the structure of Earth's soil and create habitable conditions for the evolution of plants around 700 million years ago.
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Soil microbes are everywhere, meaning they are abundant in most terrestrial environments.
This is important because these small soil microbes play a large role in supporting plant growth.
Bacterial and fungal species work together in groups (ie consortia) to support plant growth along the rhizosphere (ie the root zone of the soil) primarily by providing nutrition and preventing disease. For example, soil bacteria and fungi continue to increase the availability of soil nutrients by converting nutrients that are not available into forms that are available for plant absorption.
Microbes also act as biological fertilizer by releasing important nutrients when they die. Without microbes, plants will not have the constant supply of nutrients they need to grow.
Outside the nutritional cycle, microbes produce hormones and other chemicals to stimulate plant growth. Soil microbes can also prevent pathogenic infections by inducing plant systemic disease resistance and by coating the root surface to physically protect plants from being infected by pathogens.