Role of microbes

Microbes (bacteria and fungi) digest organic material externally by exuding a huge variety of digestive enzymes (>50 different ones) onto their food. These enzymes help chemically degrade organic detritus, breaking up large organic molecules (e.g. proteins) in which nutrient elements are bonded. Eventually, simpler molecules (e.g. amino acids) are split off and passed back through the microbial cell walls to be absorbed into their tissues and used for growth and maintenance. The simple organic molecules are eventually reduced to an inorganic form (e.g. NH4+) which plants can re-use.

This photo shows cotton strips which have been buried for 17 and 44 days and a fresh, unburied strip. The microbes have been using the cellulose fibres in the cloth as a source of energy and, by 44 days in the soil, have started to rot the strip completely away in spots. You can also see how the colonies of bacteria and fungi colonising the strips have progressively stained the strips over time.