Notes for the Foundation Courses Ch 1 Lecture 13 – The Nitrogen Cycle
Notes for the Foundation Courses Ch 1 L13 – The Nitrogen Cycle
Holly crap was this hard to wrap my head around but I did it! I got another 100% on this!
Elaine Ingham discusses the Nitrogen cycle!
As usual here is a video for the cannabis community. This video discusses cover crops for cannabis. Around the 3 min mark Rhizobacteria inoculation is discussed for the cover crops. This was briefly touched on by Elaine in the lecture. She was mentioning to find a cover crop that grows naturally in your area and harvest the nodules from the roots to help inoculate your seeds by grinding them up, adding them to a liquid biology solution and spritzing onto the seeds before planting.
On the root hairs (single celled) of a plant there are infection sites that will only allow nitrogen fixing bacteria, rhizobium to infect on those sites. Chemical signals emitted by root hair attracts the Rhizobium. When the Rhizobium infects the root hair, it curls. When this happens sugars (exudates) feed the Rhizobium and an infection thread site happens for Rhizobium emerges. This allows the Rhizobium to infiltrate the cell wall of the root hair to multiply by using the root hair sugars. The Rhizobium moves up the root hair through the growing infection site into the main root. Behaves like disease causing organism initially. When the infection sites reach main root then a lot more sugar is sent to root hair. The Rhizobium multiplies rapidly and then a nodule forms. The bacteria multiply so fast and consumes a lot of oxygen. Then the nodule becomes anaerobic in the center of it, this causes the bacteria to produce enzymes to allow it to rip apart a nitrogen molecule into a gas molecule and separate the two nitrogens and add a couple of hydrogens. Then they stick the nitrogens onto a sugar. Once this new chain of molecules are formed from add it to a carbon chain (sugars) then an amino acid is formed. Then in these conditions nitrogen is fixed. The plant receives this amino acid.
The plant expends energy in the form of sugar for this process and receives an amino acid in return. No nitrate is used in this process. It is a biological process.
Inside the nodule it will be red, or should be, red. If light red/pink or green etc., then the nodules will be considered parasitic. Hemoglobin like molecule is the cause for the red color. If not red then the nodule is taking energy away from the plant. Nodules are typically the size of marbles on the root systems of legumes.
Healthy nodules can be ground up and mixed with a liquid to be sprayed on seeds to help germination.
nitrogen diffuses into the nodule formed on root from infection of Rhizobium bacteria
Nitrogen fixing gene is expressed by Rhizobium when oxygen is used up
The correct enzymes are made by the rhizobium to break the extremely stable triple bonded C-N molecule into the N2 gas.
Rhizobium attaches the N molecules to the sugar carbon chains making amino acids.
The Rhizobium take what they need to grow while maintaining the aerobic to anaerobic conditions in the nodules. Eventually the bacteria release the amino acids and proteins to the plant.
If plant has plenty of Nitrogen then nodule will not form.
Rhizobium is limited to legumes.
free living nitrogen fixers do not need legumes
Azotobacterium, Azospirillium, etc.
they live near root system. They create a mass and when center of mass becomes anaerobic from reduced oxygen in the center of the mass they will make N. protozoas etc will eat them and release the N to the roots
Free living N fixers can release N into any root system.
need to find free living N fixers that can survive high temperatures
might need to add them to worm composts to make ideal worm composts
The plant does not give away extra N
When parts of the plant die or even all of it, then the excess N is concentrated into the biomass of the bacteria and fungi.
- The excess N consumed by bacteria and fungi remain in biomass until eaten by higher level predators/organisms from the soil food web i.e. protozoas, nematodes arthropods, etc.
The N can be much higher than the predators consuming the bacteria and fungi can tolerate. So then the excess N will be released by the predators as soluble inorganic NH4.
NH4 will stay NH4 in a fungally dominated soil due to the soil being slightly acidic.
If the N is not taken up by the plants then the N re-enters the N cycle (step 3)
Step 6 & 7 in the N cycle
A bacterial dominated soil (alkaline conditions) will convert NH4 to NO2 and then into NO3 in the process of nitrification
Nitrification requires two different types of bacteria: Nitrobacter and Nitrosomonas.
These bacteria need alkaline conditions (bacterial dominated soils) to express their enzymes and convert NH4 to NO3.
this is not the process of mineralization where we go from bacteria/fungi forms of N to predators waste in the organic mineral form.
This is a oxygen process involving hydrogen
in a bacterial dominated soil NO3 will be produced
if plants do not take up the nitrate then it will be taken up by bacteria and fungi
The N re-enters the Nitrogen cycle as either bacteria or fungi (step 3)
The N cycle happens 100s of times per hour per day
Step 8 in the N cycle
Only in anaerobic conditions will Anaerobic conditions occur
soil or compost will get to be black color
de-nitrification will occur if the correct species of anaerobic bacteria are present with sometimes yeasts will convert NH4, NO2 and NO3 to nitrous oxide or ammonia.
- Nitrogen is converted to gas and into the air.
- Only part of process of the N cycle that does not require biology
How to develop knowledge and a career in regenerative agriculture with the Soil Food Web School!
From Dr. Elaine Ingham B.A. M.S. Ph.D
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