Soil microbiology

Soil microbiology is the study of microorganisms in soil, their functions, and how they affect soil properties. It is believed that between two and four billion years ago, the first ancient cyanobacteria (also called blue-green algae) came about on Earth's oceans. These bacteria could fix carbon by photosynthesis, fix nitrogen, in time multiplied, and as a result released oxygen into the atmosphere and nitrogen into the soil. This led to more advanced microorganisms, which were important because they effected soil structure and fertility. Soil microorganisms can be classified as bacteria (including cyanobacteria and actinomycetes), archaea, fungi, algae, slime molds and protozoa. Each of these groups has characteristics that define them and their functions in soil.

Up to 10 billion culturable bacterial cells inhabit each gram of soil in and around plant roots, a region known as the rhizosphere, which is a hotspot of microbial diversity, and in particular the rhizoplane. In 2011, a team detected more than 33,000 bacterial and archaeal species on sugar beet roots.

The composition of the rhizobiome can change rapidly in response to changes in the biotic and abiotic environment. The diversity of microorganisms in soils is dependant on pH, soil texture, organic matter content, plant community composition, and contaminants such as heavy metals.