Which organisms are referred to as soil microorganisms?

Soil microorganisms primarily refer to the tiny living organisms found in the soil, including bacteria, fungi, archaea, and protozoa. These microbes play a crucial role in the soil ecosystem, particularly in nutrient cycling and decomposition processes. Among their many functions, soil microorganisms are integral to nitrogen transformation processes, such as nitrogen fixation, nitrification, and denitrification. These transformations are essential for converting atmospheric nitrogen into forms that plants can absorb and utilize, thus supporting plant growth and maintaining soil fertility.

In contrast, the other options do not accurately represent the concept of soil microorganisms. Large animals, although they contribute to soil aeration and mixing, are not classified as microorganisms due to their size. Plants, while they improve soil structure and contribute to ecosystem health, are not classified as microorganisms either, since they are multicellular organisms. Lastly, seeds themselves do not play a direct role as microorganisms; instead, they represent the reproductive phase of plants that require soil for germination. Therefore, the focus on microbes involved in nitrogen transformation processes precisely aligns with the definition of soil microorganisms.