The proper and healthy functioning of the soil depends largely on the microorganisms abundance, including the total number of bacteria and fungi, but also their diversity. The increase in the biodiversity also increases the functional capabilities of the ecosystem but from a certain point, a further increase in the biodiversity does not bring any new features, so the general biochemical and metabolic profile of the ecosystem remains constant. It is also suggested that the loss of one or more species does not dramatically affect the functioning of the ecosystem, because the same functions can be represented by many different species. This phenomenon is called a functional redundancy and makes the soil a very stable environment with a high buffering capabilities, more often called the "soil memory". On the other hand, some unique biochemical processes are characteristic for a small group of species, for example, nitrogen fixation or toxic compounds degradation. The loss of the specialized species may lead to the decrease of a rare genes occurrence in the soil, resulting in the loss of nutrients or the accumulation of toxins. This article presents the current findings on functional redundancy in terms of soil microorganisms and its implications to the soil functioning.