ABSTRACT
Most of the bacteria and fungi that inhabit the roots and aboveground organs of plants reside in the surrounding soil for some part of their lives, providing a dynamic linkage between plants and soil. Plant and soil scientists have found it helpful to think and write in terms of three respective domains – around, on, and inside plants – where diverse populations of microbes reside and interact among themselves and with plant organs. Microbiomes and plants depend upon each other in part because the microbes that inhabit plants and their surroundings contain some portion of the host plants' secondary genome. The microbiomes for both plants and animals are not amorphous aggregations of microbes. Some of the most important processes in the life of plants occur within the plant rhizosphere. Plant roots function somewhat like the intestines of mammals, absorbing nutrients and water, while acting also something like mammals' lungs.
