Probiotics And Nitrogen For Plants!
Biological Nitrogen Fixation
I found this article several months ago and am now getting around to sharing a summary of it. I chose it because it explores how microbes can make a key nutrient available for plant growth and soil health.
The article "Biological Nitrogen Fixation" explores the critical role of nitrogen in plant growth and the various processes by which plants access fixed forms of nitrogen, with a particular focus on biological nitrogen fixation (BNF).
Nitrogen is a crucial element for plant growth, forming a part of essential compounds like chlorophyll, amino acids, ATP, and nucleic acids.
Despite nitrogen's abundance in the Earth's atmosphere as nitrogen gas (N2), plants can only utilize it in reduced forms. These forms are obtained through various processes, including adding ammonia and nitrate fertilizers, organic matter decomposition, natural processes like lightning, and biological nitrogen fixation.
Biological Nitrogen Fixation (BNF) is the conversion of atmospheric nitrogen (N2) into ammonia (NH3) by specialized prokaryotes. These microorganisms, including cyanobacteria, free-living soil bacteria like Azotobacter, and symbiotic bacteria like Rhizobium and Bradyrhizobium, play a crucial role in providing fixed nitrogen to plants.
Fixing atmospheric nitrogen is an energy-intensive process, with microorganisms requiring a significant amount of adenosine triphosphate (ATP) to reduce each mole of nitrogen. This energy is obtained by oxidizing organic molecules from other organisms, photosynthesis (in the case of cyanobacteria [and other photosynthetic microbes]), or the host plant's rhizosphere (symbiotic bacteria).
The article highlights the industrial Haber-Bosch process as a common method for nitrogen fixation, but it comes with environmental consequences, including energy consumption, carbon emissions, and pollution.
Overusing chemical fertilizers has disrupted the nitrogen cycle, leading to surface and groundwater pollution. This has caused eutrophication in aquatic ecosystems, resulting in dead zones where oxygen levels become critically low, harming aquatic life.
Different ways of fixing nitrogen are discussed in the article. These include biological ways of fixing nitrogen by free-living heterotrophs, associative nitrogen fixation (like in Azospirillum), and symbiotic nitrogen fixation (like in legumes and actinorhizal plants).
The most significant nitrogen-fixing symbiotic relationship is between legumes and bacteria like Rhizobium and Bradyrhizobium. The bacteria colonize the plant's roots, induce nodule formation, and provide fixed nitrogen to the host plant in exchange for sugars produced through photosynthesis.
The article says that some strains of Rhizobium or Bradyrhizobium are host-specific and will only attach to certain types of legumes based on chemical signals sent between the bacteria and the host.
The production of leghemoglobin, a molecule similar to hemoglobin in human blood, regulates oxygen levels in root nodules, ensuring that excess oxygen does not inhibit nitrogenase activity.
Lastly, the article provides a comprehensive overview of the significance of nitrogen in plant growth, the various mechanisms by which plants acquire fixed nitrogen, and the ecological and environmental implications of industrial nitrogen fixation compared to biological nitrogen fixation. It emphasizes the importance of sustainable practices in nitrogen management to mitigate the negative impacts of excessive chemical fertilization.
Over time, I hope to cover other nitrogen-fixing probiotics that feed our microbes and plants.
Source
Wagner, S. C.. (2011) Biological Nitrogen Fixation. Nature Education Knowledge 3(10):15. https://www.nature.com/scitable/knowledge/library/biological-nitrogen-fixation-23570419/
Great work as always Eric! Going to share this on FB. Thanks 🙏
Thank you!