Single-celled organisms. The diameter of the individual is 0.5 ~ 2 microns and the length is 1 ~ 8 microns. According to the morphology of cocci, bacilli and spirillus; According to the types of nutrition, there are autotrophic bacteria and heterotrophic bacteria. According to the type of breathing, it can be divided into aerobacteria, anaerobic bacteria and facultative bacteria.

Bacteria participate in the decomposition of fresh organic matter, especially for protein (ammonifying bacteria); And participate in the transformation and nitrogen fixation of sulfur, iron and manganese. Each gram of topsoil contains millions to tens of millions of bacteria, which is the largest group of soil fungi.

2. Actinomycetes

Single-celled organisms exist in the form of slender hyphae. The diameter of mycelium is 0.5 ~ 2 microns. Streptomyces, actinomycetes, Nocardia and micromonospora are common in soil.

Actinomyces have the ability to decompose plant residues and transform carbon, nitrogen and phosphorus compounds. Some actinomycetes can also produce antibiotics and are producers of many medical and agricultural antibiotics. Every gram of topsoil contains hundreds of thousands to tens of millions of actinomycetes, which is second only to bacteria.

3. Fungi

Most of them are multicellular organisms, and some are single-celled organisms. The individual is large, and it is a branched filamentous fungus with a cell diameter of 3 ~ 50 microns. Common fungi in soil are Penicillium, Aspergillus, Fusarium and Mucor. Fungi are involved in the decomposition of starch, cellulose, tannin and the formation and decomposition of humus in soil.

Each gram of topsoil contains only a few thousand to hundreds of thousands of fungi, which is the least in soil fungi, but its biomass [refers to the weight (gram) of bacteria per square meter] is higher than that of bacteria and actinomycetes.

4. seaweed

Algae in soil are mostly unicellular organisms, but there are also multicellular filaments. It is 3 ~ 50 microns in diameter, likes humidity, mostly lives in the surface layer or topsoil of soil, and the number is less than that of fungi. Green algae, cyanobacteria and diatoms are common in soil. Some species in cyanobacteria can fix nitrogen in the air.

5. Protozoa

Single-celled organisms. Feeding on plant residues and fungi. Rhizopoda, ciliates and flagellates are common in soil.

Impact:

1, decomposes organic matter and directly participates in the biological cycle of carbon, nitrogen, sulfur, phosphorus and other elements, so that the nutrient elements needed by plants are released from the organic matter and reused by plants.

2. Participate in the synthesis and decomposition of humus.

3. Some microorganisms have the ability to fix nitrogen in the air, dissolve insoluble phosphorus in soil and decompose potassium-containing minerals, thus improving the nutritional status of nitrogen, phosphorus and potassium in plants.

4. The products of life activities of soil organisms, such as growth stimulators and vitamins, can promote the growth of plants.

5. Participate in the redox process in the soil. All these actions and processes occur with the help of the chemical behavior of enzymes in soil organisms, and change the physical and chemical properties of soil through mineralization, humification and biological nitrogen fixation.

In addition, mycorrhiza can also improve the nutrient absorption capacity of some crops.

Extended data:

I. Soil microorganisms

Components of soil organisms. Refers to living organisms in the soil that cannot be distinguished by the naked eye. It can only be observed in the laboratory with the help of a microscope or an electron microscope. Generally, it is measured in micron or nanometer. Soil microorganisms have great influence on the formation and development of soil, material circulation and fertility evolution.

Living organisms in soil that cannot be distinguished by naked eyes and can only be observed by microscope or electron microscope. Most of them are single-celled organisms. Include bacteria, actinomycetes, fungi, algae and protozoa. Most microorganisms saprophyte in the soil and obtain energy and nutrients through ready-made organic matter.

The main functions of soil microorganisms are: to participate in the mineralization and humification of soil organic matter and the redox reaction of various substances; Participate in the circulation of soil nutrients and promote the availability of plant nutrients; Microorganisms living in rhizosphere and symbiotic with plants can directly provide plants with nitrogen, phosphorus, other mineral elements and various organic nutrients.

Can provide effective strains for industrial and agricultural production and medical care; Some antibacterial microorganisms can prevent and control the harm of soil-borne pathogens to crops; Degradation of residual organic pesticides, municipal sewage and factory waste in soil, reducing the harm of residual poison; Some microorganisms can be used in biogas fermentation to provide bioenergy, fermentation broth and residual organic fertilizer.

Second, the soil impact.

Soil organisms have a great influence on soil properties and also affect the purification function of soil pollutants. Their function is to chew and decompose animal and plant residues and make them degrade continuously; Turn and stir soil minerals and organic matter to promote the formation of soil aggregate structure.

Soil organisms have a certain tolerance limit to pollutants entering the soil, which will weaken or even endanger their life activities and survival, thus reducing or destroying the purification function of the soil.

Baidu Encyclopedia-Soil Biology