What Do Microorganisms Do in the Nitrogen Cycle?

Microorganisms are tiny living things that play a huge role in the nitrogen cycle. This cycle helps keep our environment healthy and helps plants and animals grow. The nitrogen cycle includes several important steps: nitrogen fixation, nitrification, ammonification (or mineralization), and denitrification. Let’s look at what each of these steps means and how microorganisms help.

1. Nitrogen Fixation:

   • This step changes nitrogen from the air ($N_2$) into ammonia ($NH_3$), which plants can use.
   • Special bacteria, like Rhizobium, work with plants called legumes, while other bacteria, like Azotobacter, can live on their own.
   • These microorganisms help fix about 100 million metric tons of nitrogen each year. That’s a lot!

2. Nitrification:

   • Nitrification converts ammonia into nitrite ($NO_2^-$) and then into nitrate ($NO_3^-$).
   • This happens in two parts:
     • First, bacteria called ammonia-oxidizing bacteria (like Nitrosomonas) change ammonia to nitrite.
     • Next, nitrate-oxidizing bacteria (like Nitrobacter) turn nitrite into nitrate.
   • Around 40% of the nitrogen that comes from decayed plants and animals gets processed this way by microorganisms.

3. Ammonification (Mineralization):

   • During ammonification, microorganisms break down dead plants and animals to release ammonia back into the soil.
   • Fungi and bacteria are the main helpers in this step, recycling nitrogen compounds.
   • About 80% of nitrogen from plant materials returns to the soil through ammonification.

4. Denitrification:

   • Denitrification is where bacteria change nitrates back into nitrogen gas ($N_2$) or sometimes into nitrous oxide ($N_2O$). This completes the nitrogen cycle.
   • Important bacteria for this step include Pseudomonas and Bacillus.
   • It's believed that denitrification removes about 40% of nitrates from the soil, stopping too much nitrogen from building up, which can cause water pollution.

5. Conclusion:

   • In short, microorganisms are key to keeping nitrogen balanced in our ecosystems.
   • They help turn nitrogen into forms that plants can use, which is essential for farming and growing food.
   • The way nitrogen moves through ecosystems can also affect different plants and animals living there. About 75% of nitrogen in some soils becomes available to plants thanks to microbial activity.

In summary, microorganisms are vital for the nitrogen cycle, helping to support life on earth, encourage biodiversity, and boost farming systems. The numbers show just how much nitrogen they help convert and how important they are for keeping our ecosystems healthy!