Rhizobium is a bacterial group that exists widely in the environment and often nodulates nitrogen-fixing in symbiosis with leguminous plants. It plays an important role in the sustainable development of agriculture, forestry and animal husbandry.
In recent years, studies have found that in addition to the well-known nitrogen fixation function, rhizobia also participates in the restoration of heavy metals, organic matter and other polluted soils in the environment, and plays an important role in ecological environment restoration, maintenance of land productivity, and energy conservation and emission reduction.
In particular, the combined effect of rhizobia and legumes in remediating polluted environment is more significant.
Effects of Rhizobia on Agricultural Production
In agricultural production, rotation and intercropping between rhizobia and leguminous crops can improve soil fertility and play a crucial role in increasing crop yield.
Since rhizobia can grow and multiply in the roots of crops, the reproduction opportunities of pathogenic microorganisms are blocked. At the same time, rhizobia can also induce systemic resistance in plants, reduce the probability of crop disease and improve its disease resistance.
After soybean inoculation with rhizobia, it can reduce the use of nitrogen fertilizer, effectively alleviate and improve soybean stubble and root rot, significantly improve the quality and yield of crops; and reduce environmental pollution caused by a large number of chemical fertilizers and production of chemical fertilizers.
Rhizobium can also enhance the drought resistance of crops. In addition, many studies in recent years have shown that rhizobia also play an important role in the remediation of heavy metals, organic matter and other contaminated soils.
Effect of Rhizobia in Remediation of Contaminated Soil
Rhizobium not only has the ability to degrade organic pollutants and resist heavy metals, but also stimulate the survival and action of other degrading bacteria, thereby reducing the concentration of pollutants.
Its symbiotic nodulation and nitrogen fixation with leguminous plants can promote plant growth and enhance plant disease resistance and stress resistance.
It can repair the polluted soil of industrial waste land such as salinity, heavy metals, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, etc., and plays an important role in the restoration of the ecological environment.
The symbiotic system formed by rhizobia and legumes:
On the one hand, plants provide a living place for microorganisms, and nutrients such as root exudates, exfoliants and enzymes can promote the growth and reproduction of flora and enhance the combined degradation of microorganisms;
On the other hand, microorganisms can degrade pollutants or change the existing form of pollutants, reduce the toxicity of pollutants to plants, improve the tolerance of plants, and promote the absorption of pollutants by plants.
Effect of Rhizobia in Remediation of Heavy Metal Soil
The resistance and detoxification mechanism of rhizobia to heavy metals are mainly due to the following aspects:
(1) Rhizobium can reduce the permeability of the outer cell barrier to heavy metal ions, thereby effectively sequestering a large number of heavy metals.
(2) The outer cell barrier includes not only cell membrane and cell wall, but also accessory structures such as exopolysaccharides, lipopolysaccharides, capsular polysaccharides, and glycoproteins. These accessory structures adsorb heavy metals to form complexes to reduce the harm of heavy metals to cells.
(3) When heavy metals enter cells, cells can reduce the toxicity of heavy metals by chelation of cytosol, separation of cell vacuoles, and binding of cytoproteins to heavy metals.
(4) Rhizobia can also use efflux to expel part of heavy metals from the cell to avoid excessive accumulation of heavy metals in the cell.
Effect of Rhizobia in Remediation of Organic Contaminated Soil
Studies have shown that rhizobia are resistant to many organic pollutants, such as antibiotics.
At the same time, it can degrade phenol, polychlorinated biphenyls, trinitrotoluene, polycyclic aromatic hydrocarbons, dibenzothiophene, 2,4-dinitrotoluene, etc.
Effect of Rhizobia in Saline Soil Remediation
Long-term planting of legumes in the soil, salinity content, pH value significantly decreased, and organic matter, nitrogen content increased significantly. Because legumes have biological desalination, they absorb soluble salt ions in the soil, accumulate in plants, and are taken away with the transfer of plants, thereby reducing soil salinity.
The rhizobia – legumes have a strong nitrogen fixation effect, which can increase soil biomass. And with the growth of plants, fine roots, nodules and fallen leaves continue to fall off. After these organic substances are decomposed, the content of soil organic matter is increased.
Rhizobia can not only effectively increase the yield of leguminous plants and improve soil fertility, but also repair soil polluted by heavy metals and organic matter, which has positive significance for agricultural production and environmental restoration.