Bacteria and Fungi:
Nature's Tiniest Recyclers
Many people equate bacteria with disease and fungi with rot. But in fact, the vast majority of bacteria and fungi are beneficial to life on earth.
These two classes of microbes are irreplaceable parts of the organic web of life. Without them your garden would not grow. Without them, organic gardening would not be possible.
Bacteria and fungi perform many almost miraculous tasks in the garden. In instance, they lock up plant nutrients until they’re needed. This greatly reduces the reducing leeching of those vital nutrients from the soil. They also help retain water in the soil, near your plants’ roots where it’s needed.
But probably their greatest contribution to your garden—and to the organic web of life—is as the earth's main decomposers. They take dead plant and animal material and break it down into components that other plants and animals are able to “eat.”
Channeling energy from the sun
for growth and reproduction
It’s normal to think that eating involves biting, chewing and swallowing (after all, that’s how we and other large animals do it). But in fact, all living things need to eat—that is, they need to ingest energy and nutrients in order to grow and reproduce.
Here’s how bacteria and fungi carry energy from the sun to plants, animals and you.
The sun provides the ultimate source of energy on earth. Through the process of photosynthesis, green plants convert the sun’s light energy, carbon dioxide (CO2), and water (H2O) into simple sugars.
These simple sugars contain only carbon (C), oxygen (O), and hydrogen (H). (This becomes important later in the story). This energy-harvesting process occurs in plants as tiny as one-celled alga and as massive as giant redwoods.
All green plants turn these simple sugars into more complex chemical structures such as starches and proteins. Larger green plants then convert these components into more complex structures like leaves, stems, bark, and roots.
While complex in its details, this process of harvesting the sun’s energy for most life on earth might seem straightforward. But there’s one huge problem with the way I’ve described it.
Animals and plants need more to survive and reproduce than sugars and starches. They need proteins, DNA, RNA, fats, vitamins, and other substances that contain elements other than carbon, oxygen, and hydrogen. They need nitrogen, sulfur, phosphorus, potassium, and numerous other minerals.
And the process of photosynthesis does not provide these last crucial elements.
Where do they come from? Plants are able to absorb most of the sulfur and many soluble minerals directly from the water or soil they live in. But they’re not able to absorb all the nitrogen they need that way.
How does nitrogen get into plants? This is where bacteria and fungi come into the picture.
Bacteria and fungi—harvesting nitrogen
for all living organisms
Nitrogen is the most common component of air—but in the form of a two-atom molecule N2 (called molecular nitrogen). Plants can’t use molecular nitrogen. They’re unable to break the bonds holding the two nitrogen atoms together to release nitrogen in a form plants can use to make proteins.
However, a special class of bacteria called nitrogen-fixing bacteria are able to break this bond. By a special, symbiotic relationship with plants, these bacteria provide them with usable nitrogen.
Problem solved, so it seems. But it isn’t. Once nitrogen and sulfur are used by plants to make proteins and other biochemicals, these elements are “locked up.” They’re locked up inside the animals and other plants that eat them.
Some of these important life-sustaining elements (nitrogen, carbon, sulfur, and others) are excreted as waste material. Some remain in organisms the original nutrient providers ate until that organism dies.
These crucial elements would stay in the waste material and the dead organisms if it weren’t for bacteria and fungi.
These tiny organisms—in a process we turn our noses up to and call “decay”—release these locked up elements. They recycle them.
You may have heard in elementary school that if it weren’t for bacteria and fungi, we’d be walking knee deep in excrement and dead animals and plants. But bacteria and fungi’s role is far more important than that.
If it weren’t for these tiny recyclers, we wouldn’t even be walking around. Without these microbes, animals and most complex plants would not have the nutrients they need to grow and reproduce.
So, the bottom line for you as a conscientious organic gardener: If you want to harness the organic web of life in your garden, you must “pamper” the bacteria and fungi that make your garden grow.
That pampering starts with knowledge. So here’s your “short course” on the details of the roles bacteria and fungi play in the organic web of life.
Understanding bacteria and fungi
so you can optimize their power in your garden
A Short Course on Bacteria and Your Garden
What they “eat” |
- Bacteria decompose both dead plant & animal material and take in nutrients released by the decomposition.
- Bacteria do best with “green” material (fresh plants, no woody parts).
- Root exudates are favorite foods for some bacteria, so there can be huge populations of these bacteria near roots (called the rhizosphere).
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Who they feed |
- Other members of the web get food and energy by eating bacteria. If there are not enough bacteria or they’re killed by chemicals or over tillage, the entire organic web of life in your garden suffers.
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Element recycling |
- Bacteria play a crucial role in recycling carbon, nitrogen, and sulfur.
[See Figure 1].
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Nutrient retention and release |
- Bacteria lock up nutrients in their cells that otherwise would disappear through leeching. Since bacteria attach themselves to soil particles, these nutrients stay in the soil, close to plant roots.
- When bacteria die, fungi and other microbes scavenge their bodies, releasing locked-up nutrients back into the soil.
- Bacteria don’t travel far therefore the nutrients stay close to the roots.
- Thus, bacteria can be viewed as living fertilizer containers.
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Special considerations |
- Bacteria generally prefer alkaline soil conditions (pH above 7). Most vegetables, annuals, and grasses prefer bacterially dominated soils.
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Special problems and solutions |
- Many anaerobic bacteria (bacteria that grow in the absence of air) are toxic to plant life, other bacteria, and humans. They are usually bad smelling, suggesting rotting and putrifaction.
Conditions promoting anaerobic bacteria include poor soil texture, lack of soil pore space, standing water, and soil compaction.
These conditions can result from excess tillage of the soil.
- Artificial insecticides, chemical fertilizers, and non-organic approaches to plant culture can kill bacteria, fungi, and other beneficial microbes.
- Solution to these problems: Bacteria compete with each other. When conditions for bacterial growth are well maintained, the “good” bacteria win out against the anaerobic and other dangerous bacteria.
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Figure 1: The Nitrogen Cycle1 |
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A Short Course on Fungi and Your Garden
What they “eat” |
- Like bacteria, fungi break down both dead plant & animal material. But they also eat dead bacteria, releasing nutrients stored in bacterial cells.
- Fungi are the primary decomposers of the organic web of life.
- While some fungi prefer easier-to-digest sugars, most prefer hard-to-digest “brown” material like dried leaves and woody parts of plants.
- Fungi are able to penetrate hard surfaces including plants, insect shells, and bones. This ability to penetrate surfaces results in release of important inorganic minerals for plant (and ultimately animal) use.
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Who they feed |
- Some fungi exude nutrients while alive. But most release their stored nutrients when other organisms eat them. They also release their nutrients and feed the soil when they die and decay.
- Some fungi called mycorrhizal fungi form a special symbiotic relationship with plant roots. They produce microscopic threads that penetrate root hairs, transporting nutrients from the soil directly into the plant.
- Without mycorrhizal fungi, plants could not obtain the variety or amounts of nutrients they need to grow optimally. For this reason, your gardening practices should protect these special fungi.
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Element recycling |
- As with bacteria, fungi play a crucial role in recycling carbon, nitrogen, and sulfur. [See Figure 1].
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Nutrient retention and release |
- Fungi lock up nutrients in their cells that otherwise would disappear through leeching.
- Like bacteria, fungi immobilize nutrients they take in. These nutrients are released later when the fungi die or other organisms eat them.
- So, like bacteria, fungi are living fertilizer containers.
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Special considerations |
- Fungi generally prefer acidic soil conditions (pH below 7). Most shrubs, trees, and woody plants prefer fungi-dominated soils.
- Mycorrhizal fungi unlock and transport copper, calcium, magnesium, zinc, and iron for plant use.
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Special problems and solutions |
- Artificial insecticides, chemical fertilizers, and non-organic approaches to plant culture can kill fungi.
- Tillage of garden soil destroys the microscopic threads of beneficial mycorrhizal fungi, reducing nutrient uptake by plants and trees.
- Solution to these problems: Reducing or eliminating tillage, use of organic fertilizers, and avoidance of chemical insecticides and other materials protects the fungi-plant symbiosis while allowing fungi to grow and thrive naturally.
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Biochar, bacteria, fungi…
and your garden
Soil scientists are just starting to gather a significant body of data showing biochar’s beneficial effect on soil microbes. But there is an ancient “laboratory” that gives strong evidence that biochar encourages growth of these beneficial organisms.
Terra preta—the dark earths of the Amazon which are rich in biochar—are also significantly richer in microbial activity, composition, and mass than the surrounding areas that lack biochar amendment.
This historical insight provides evidence of the beneficial relationship that exists between biochar and microbes including bacteria and fungi.
But there are some very exciting results from modern experiments as well.
Dr. Paul Blackwell has been working since 1988 to improve the soils in Western Australia. At a 2007 International Biochar Initiative meeting in Terrigal, Australia, Dr. Blackwell presented findings reached on his work with biochar.
His results were very positive. He established the biochar probably helped the seed-applied microbes survive better in a dry soil environment at planting.2
Another experiment demonstrates visually the direct effect of biochar as seen in Figures 2, 3, and 4. These photos show the growth of plants that had been grown in just biochar and in biochar with added mycorrhizal fungi after 75 days.3
The plants grown with biochar and added fungi [Figure 4] showed significantly darker and more dense plant growth at the 75-day mark than the control plants [Figure 2] or those grown just with biochar [Figure 3].
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Figure 2: Control plants (no biochar or fungi) |
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Figure 3: Plants grown only in biochar.
Note the improved growth after 75 days over the controls. |
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Figure 4: Plants grown in biochar with additional mycorrhizal fungi.
Note greater growth and darker foliage. |
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This result is a good indication of the mutually beneficial interaction between biochar and mycorrhizal fungi.
The theory behind this positive effect is that biochar improves soil porosity, giving beneficial bacteria and fungi favorable living conditions. It’s also suspected that biochar’s own pores provide good growing places for beneficial microbes.
More research needs to be done to determine the exact causes for biochar’s ability to improve the interaction of beneficial bacteria and fungi in your garden. But results such as these demonstrate that biochar can be an important and effective amendment for the organic web of life… and for your garden.
Editors Note : This is a greatly simplified picture of a tremendously complex process. For example, there are bacteria in deep ocean trenches where sunlight never reaches that use a process similar to photosynthesis to harness energy from sulfur that bubbles in the trenches.
But for our purposes, I’m going to keep it simple.
References:
- Adapted from: http://ssil.uoregon.edu/hum399/gallery/week10/29c.NitrogenCycle.jpg
- http://www.biochar-international.org/paul/blackwell
- http://terrapreta.bioenergylists.org/flanaganrhcvamfeb08
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