Certain microorganisms play a vital role in facilitating the transformation of nitrogen in the soil. The key organisms involved in nitrogen cycling include:
Nitrogen-Fixing Bacteria: These bacteria, such as Rhizobium and Azotobacter, have the ability to convert atmospheric nitrogen (N2) into a usable form, such as ammonium (NH4+). They form symbiotic relationships with certain plants, commonly legumes, and reside in nodules on the plant roots.
Nitrifying Bacteria: Nitrifying bacteria convert ammonium (NH4+) into nitrites (NO2-) and then into nitrates (NO3-). The two important groups of nitrifying bacteria are Nitrosomonas, which performs the first step of oxidation, and Nitrobacter, which carries out the second step.
Denitrifying Bacteria: Denitrifying bacteria convert nitrates (NO3-) back into atmospheric nitrogen (N2), completing the nitrogen cycle. These bacteria operate in low-oxygen environments and help mitigate the buildup of excess nitrogen in the soil. Examples include Pseudomonas and Paracoccus species.
Ammonifying Bacteria: Ammonifying bacteria decompose organic nitrogen compounds, such as dead plants and animal waste, into ammonium (NH4+), making it available for other nitrogen-transforming organisms.
Mycorrhizal Fungi: These symbiotic fungi establish mutualistic associations with plant roots. They enhance the plant's nutrient uptake, including nitrogen, by extending their filamentous structures (hyphae) into the soil, increasing the surface area for nutrient absorption.
These organisms collectively participate in the processes of nitrogen fixation, nitrification, denitrification, and ammonification, which are essential for cycling nitrogen through various forms in the soil and making it available for plant growth.