Microorganisms as natural aids in
Gardening and Agriculture
By Dr. Ursula Frimmer, Mikrobiologin @ Biosa Danmark ApS
Obviously the knowledge between many garden lovers and farmers of using
microbial products as a natural promoter of soil fertility (soil aid) and plant health
(plant aid and stabilisation), could be better. The lack of understanding may be an
equation of being unable to sight these “nano” helpers and a draw back on a scientific
approach, preventing a flow of information to the public about the complicated
processes going on in the soil. This article is an attempt to enhance the understanding
and explain the importance of the great work done by the billions of invisible helpers.
By the way, did you know in a handful of good humus soil, you’ll find far more
living beings than humans on the entire planet? In just one gram of soil, you’ll find
several billion active bacterias, millions of funguses plus thousands of invisible insects.
The average amount of biomass per hectare is 15 tons. About one third of the biomass is
produced thanks to the good work done by bacteria.
The microbial involvement in the cycle of elements
By trying to understand the role the microbes are playing, it becomes clear how
dependent we are on them. They are critical to the survival of every living species on
earth, humans, animals and plants.
From the sun’s energy, green plants produce organic substances; carbon
dioxide (CO2) from the air and from “dead” leaves, roots, stems the microbes
produce inorganic plant nutrition, such as phosphate and nitrate (chemical
sugars, strength, cellulose, lignin, protein, fat and many other matters.). That’s
why they are called Producers.
Animals are called Consumers, because, in order to build up their body
mass, they consume most of the primary Biomass available, as feed.
Finally Animals and plants die, but in order to close the life cycle, the
remaining organic substances need to be broken down and converted into
mineralised, inorganic compounds. The decomposition process is primarily
handled by funguses and bacterium. In the ecosystem they are called Destructors.
Without them, life on earth wouldn’t be possible.
Just by looking at the life cycle of Carbon, the importance of microbes becomes
more understandable. As they are responsible for the mineralisation of organic carbon
produced by green plants, they become “key” in maintaining an ecological balance. The
amount of carbon oxide in Atmospheric Oxygen is slightly more than 0.03%. The entire
photo-synthetic production from green plants is so big that the CO2 stored in the entire
atmosphere, would be exhausted within a 20-year time period. If it wasn’t for the
microbes, the entire earth surface plus volumes of all the water in our oceans would be
covered and infiltrated by organic substances. The Microbes are responsible for the
conversion of organic substances into a mineralised compound. Through the oxidation
process, carbon is once more being released as CO2.
The microbes play similar roles in other cycles (nitrogen, sulphur, and
phosphor). An example, Nitrogen in soil, originating from dead plants and animals etc.,
is present as Ammonium, a compound not absorbable by plant roots. But following a
microbial oxidation into Nitrate and Nitrite, the Nitrogen becomes absorbable – in other
words, the cycle is closing itself, the cycle becomes complete.
Microbes and plant nutrition
Summarized, it is fair to conclude that when microbes are acting as
“Destructors,” they are maintaining the supply chain with essential elements necessary
for all life cycles. Due to the restless work converting organic soil-related substances,
e.g., roots, leaves, greens, guelle, manure, dead animals etc. into an inorganic
compound, e.g., nitrogen compounds, Carbon dioxide, minerals, thus plant-available
nutrition, they make it possible for life on earth to continue. If it were not for them
mineralising all soil-related organic substances, plants would simply be starving,
because, unlike animals and human beings, plants are unable to obtain and utilise
complex organic compounds like cellulose or proteins.
Specialised microbes are actual starting the breaking down process, but because
of a catalytic impact of their enzymes, they are only able to take the process to a given
level. Then, following a given pattern various specialised groups of microbes, replacing
each other, are accomplishing the conversion of organic substances into mineralised
forms. The pattern itself however, is being influenced by many environmental variables,
such as temperature, humidity, pH-value, concentration of nitrogen compounds.
The conversion time is by no means the same, the time is depending on the type
of organic substance being processed, whether the substance is originating from plant
or animal. The breakdown of Carbohydrates (Sugar, Starch, Cellulose, Hemicelluloses
respectively Polyosen, Petkin etc.) Proteins and Protein derivates are not that
complicated, whereas substances like Lignin, many Greases, Harts, VAXES, Rubber, etc.
are more difficult to convert. The natural substances are the difficult ones to breakdown
and convert, they belong to a group, which scientists refer to as the “Intermediate
Compounds” a group, which is playing a very essential role, when it comes to the soil
quality.
Both growth and yield is depending on which extent the interaction between
microbes and plant roots is going on. An efficient and continuous supply of nutrients to
the plants is the function of well working microbial life in the soil.
“Our research clearly shows that an effective utilisation of carbon hydrates, subs
consequently the creation of fertile humus soil, is a function of the diversity of the
microbes in soil.” (Paul Maeder, FiBL, Research institute for biological Agriculture,
Switzerland).
With understanding and knowledge one can build up a diverse micro flora, thus
secure an effective conversion of organic substances into available plant nutrition. In
addition to practising good soil management, the clue is to add enough organic matters
to the soil. By integrating plant matters into the crop rotation creates a much more
diverse micro flora, capable of suppressing the survival of phyto-pathogen bacteria,
which is a part of a living soil, as well.
Reciprocal effect between plants and microbes
Similar to human and the animal surfaces, each single part of the plant above soil
is colonized by microbes. They are a part of an integrated ecological system, similar to
the natural flora on the human skin and on the mucous membranes.
However, the processes taking place underground are worth paying attention to.
For years it was anticipated that the function of the root system was to absorbing water
and nutritional matters from the soil. To day we know, the root system is not limited to
absorbing water and other nutritional matters, but to secrete a variety of substances like
sugar, enzymes or organic acids, as well. These substances are both supporting the
extraction of plant nutrition’s from the soil and serving as nutrition for both bacterias
and fungi. In that narrow region of soil that is directly influenced by root secretions and
associated microbes also referred to as the Rhizosphere, the number of bacteria is much
higher than in “bulk” soil. The microbes in “bulk” soil are not distributed uniformly
around the soil; they are congregated around nutrient sources. A nutrient source for
these microorganisms is organic matter. (Curl, 1986)
A fair question to ask “Why do plants feed microbes?”
Scientists used to ask that question. In the meantime, some inter related systems
have been explored and investigated. One of these systems is the symbioses between the
nitrogen fixing Rhizobium bacteria and Leguminous.
A plant does not have the ability to obtain and utilize the less reactive Nitrogen
(N2) from the air. Over the root system, the plant is only able to obtain Nitrogen in form
of Nitrite and Nitrate. Among the Rhizobium bacterias, many are capable to activate
elementary nitrogen (N2). From the view of a plant, because Nitrogen and Phosphor are
growth related factors, insufficient supplies of these do influence the growth negatively.
The Rhizobein bacteria are infecting the host-specific young root hairs, where
they are craving a type of infection canal, through which the bacteria are growing toward
the core of the root hair. Gathered together, plant and bacteria create a tissue bruise and
swelling, where the bacteria begin to repopulate. The perfect symbioses of a perfect win,
win situation. By supplying nutrition’s like sugar to the bacteria, the plants, as host, are
providing the best possible environment for the repopulation. Since their start in the 90’
the company Danisco has been working on isolating beneficial Rhizosphere bacteria
from a sugar beet. In the meantime Danisco succeeded, not only in isolating some strains
and even to secure their durability, but in linking the strains to a substrate (called
“carrier”), then implement both strains and carries together into the seed of a sugar beet.
But the Rhizosphere is not just for beneficial bacteria’s, also disease coursing
gems and pathogens, capable to threatening plant health are living there, however in
healthy soil these are being prevented from spreading improperly by “control” organism,
an organised biological control is in place.
Founded on our knowledge between the plant Genome and the microbes in the
Rhizosphere, studies in the signal exchange and signal processing adjacent to the roots
had renewed attention.
Recent research shows that the bacteria present in the Rhizosphere, do
communicate. The language is of chemical nature, but influenced by the density of a
bacterium’s population, molecules selected as “signal” molecules (N-Acyl-
Homoserinlactone) are able to regulate certain genes and/or start-up the production of
defensive bacteria to suppressing unwanted guests (biological control). It is obvious that
by using the mentioned “signal” molecules, bacteria within the Rhizosphere, are able to
communicate by “speaking” the chemical language.
In the meantime researchers succeeded in observing a reaction on a tomato plant
coursed by a “signal” molecule of the bacteria strain -Serratia liquefacies. Therefore we
may assume that on the one hand an active exchange of information between plants and
Rhizosphere bacteria are going on and on the other hand, even among bacteria’s
themselves. Even single cell organisms like Amoebas and more sophisticated animals,
like insects, do communicate. When Amebas are feeding on microbes living on the root,
distant part of the plant, e.g., leaves and roots are reacting. Another example
demonstrates the complexity of these connecting reactions: When a larva is feeding on a
plant leaf, the composition of microbes on the root is changing.
The influence of soil microbes, as an integrated part of the entire soil related eco
system including plant roots, should not be underestimated.
With certainty we know that soil microbes are influencing the plant nutrient
supply chain positively, its growth and its ability to survive attacks from pathogens and
on soil fertility. Scientific efforts done to understand and explain these effects in details
are, despite new and sophisticated methods, in an initial stage. There is a real hope that
the gained knowledge will promote a new type of cultivation, which enhances the soil
fertility by reducing the deployment of chemical herbicides and pesticides.
Today both farmers and gardeners have access to a wide range of natural,
microbial products; alternatives that either substitute or complement; eliminate the need
for conventional products. The principles of biotechnology are substituting the use of
artificial and chemical products in agriculture with clean and natural methods that are
already here.
