Organisms are either autotrophs that obtain energy and carbon from inorganic sources, or heterotrophs that obtain energy and carbon from organic sources. Earthworms have an enormous effect on the soil through their mixing of soil material and by ingesting organic matter. The organic matter remaining n their casts is partially digested, so the nutrients in it are more available to plants. Termites digest large amounts of organic matter, some of which is later available to plants, and also affect soil physical properties. Other arthropods are predators, feeding on other organisms.
Nematodes are often predators in the soil, feeding on other microorganisms.
Many of them have a detrimental effect on plant growth. Microscopic protozoa graze on bacteria, moving within thin films of soil water. When water or food are limiting they encyst, waiting until conditions improve. Plants have major effects in the soil environment by the cycling of water and nutrients, production of organic matter, formation of pores by root growth, secretion of root exudates which promote soil aggregation, and production of organic acids which influence nutrient availability. Bacteria have perhaps the greatest influence in the soil environment of all organisms.