The soil has diverse communities of organisms, as
well as complex biological functions, which enable plants and crops to grow. In
addition, people use pesticides in order to get rid of pests that can harm the
plants’ health. Its use influences the microbes around it, and has consequences
for the soil. Herbicides, pesticides, as well as other chemicals and pollutants,
can disrupt biological functions in the soil, and can even reduce the amount of
CO2 in it (Mishra 2004). Even worse, if these accumulate in the soil, it degrades
it at a later point. Currently, scientists believe that using bacteria and
nutrients can help plants and soil against damage by chemical pollutants, which
would enable plants and crops to keep growing healthy.
According to Upasan Mishra and Dolly Wattal Dhar’s
paper, “Biodiversity and Biological Degradation of Soil”, pesticides can reduce
the amount of CO2 production, degrade cellulose, and can inhibit biological
function in the soil. For example, at normal doses, amitrole, 2,4-DB, and
diallate can inhibit nitrification for about eight weeks (Mishra 2004). This is a longer inhibition period than
atrazine, bromacil, picloram, and simzine, but that doesn’t mean that these
four pollutants are nay better. Damage to the soil can also inhibit the plant
from absorbing nutrients available in the soil, if they have not died already. Repairing
the damage done to it would take a long time, but even if this were
accomplished, the soil would never return to its original and pristine state.
A study from 2012 shows that even dead
bacteria is important for the soil because its converted into soil components.
It was commonly assumed that organic components in the soil were made from
decomposed plants, but the truth is that degraded plant material is initially
convereted into microbial biomass, that then provides source for soil
organic matter (Arnhold 2012). This is imortant because part of the reason why
CO2 escapes unto the atmostphere is because of the degraded organic material in
soils. This will affect climate, which will also have an effect on soil
fertility. This fact emphasises the imporatnce of keeping soil healthy. To
prevent this from happening, its important to ensure that soil is healthy
enough for plants and crops to grow in. Since long term effects from soil
pollutants inhibit biological processess, and has the potential to damage soil,
we must look at other alternatives to keep soil fertile and healthy, even if
its no longer in its pure state. However, to accomplish this, soil’s
relationship with plants, bacteria, and nutrients needs to be understood.
Strategies for repairing damaged soil, and to grow
healthy plants, all have one thing in common; the relationship between plants
and the soil. This relationship is basically the plants interacting with the
soil whether it’s the plant absorbing nutrients from the soil, or building immunity
against bad bacteria in soil. In Amy Coombs’ article, “Fighting Microbes with
Microbes”, an experiment with tomato plants is used to explain a mechanism of
the relationship in action. During the experiment, tomato plants were covered
with plastic bags for a time; part of the tomato plants, inoculated with the Alternaria
solani fungus, had their fruit rot. Meanwhile, the rest, that were not
inoculated, were able to build a defense against the fungus, and made enzymes
that would fight against the fungus. Why?
An interaction between the soil
and a different fungus was found to a possible cause; the Glomus Mosseae, which
attaches itself to the plant’s root hair, forming a symbiotic relationship with
the plant. In other words, this warns the plant, through the roots, to create
defenses against Alternaria solani. Researchers
are certain that, based on this discovery, “the mycorrhizal network can extend
from one set of plant roots to another, it’s possible that the network of
fungal mycelia acts like telephone wires, allowing the plants to communicate
underground” (Coombs, 2013). However, this is currently just a hypothesis; not
much is known to researchers about the specific details of this mechanism, so how
this relationship works is not completely understood yet. If this hypothetical communication
were understood and proven to be correct,
then scientists would use this as a way to prevent disease in plants by
cultivating a mix of good microbes into the soil to accomplish this goal. The
benefit from this would be that the amount of pesticides, and other chemical
products generally used in soil, would be reduced. This in turn would reduce,
or prevent, further damage to the soil by pollutants.
A research paper by Richardson et
al, “Plant and Microbial Strategies to Improve Phosphorous Efficiency of
Agriculture”, suggest a different alternative. It outlines three possible
strategies where plants and
microorganisms could possibly improve phosphorous efficiency “(i) Root-foraging
strategies that improve P acquisition by lowering the critical P requirement of
plant growth and allowing agriculture to operate at lower levels of soil P;
(ii) P-mining strategies to enhance the desorption, solubilisation or
mineralisation of P from sparingly-available sources in soil using root
exudates (organic anions, phosphatases), and (iii) improving internal
P-utilisation efficiency through the use of plants that yield more per unit of
P uptake” (Richardson et al 2011). The Richardson team believes that
P-efficient plants can be created if “architecture” and root growth is modified,
through root manipulation or by managing mycorrhizal fungi and microbial inoculants.
However, the success from the
genetically manipulated plants to enhance nutrient secretion from roots, is
very difficult to repeat outside controlled
lab procedures due to variable results given after being evaluated in soil. The
team concludes that understanding “trait interactions and the ecophysiology of
the rhizosphere is emerging as an important factor in development of improved
plants via these P-efficiency routes”, because it’s important to consider this
when trying to breed plants for P-efficieny (Richardson et al). According to
the article, these novel P-efficiency plants (with better root traits and extracting
genotypes) can be beneficial in an agro-ecological and socio-economic system
level, as it can lessen P-depletion.
In another study, the “Using soil
bacteria to facilitate phytoremediation” paper by Bernard R. Glick, explored
the possibility of using soil bacteria with plants to remove pollutants from
the soil. Here, pythoremoderation (where plants are used to remove pollutants
from soils and water) would be assisted by soil bacteria to work against
organic and metallic contaminants. Glick hopes that not only could phytoremediation
be facilitated, but future field research studies as well when dealing with
toxic contaminants and pollutants (Glick 2010).
Unfortunately, there were complexities
during the experiment that made it difficult to create an ideal set of
conditions that can work for all phytoremediation experiments. These ranged
from plant type, added bacteria, and soil composition, to conditions of
contaminants found in soil and temperature range. There was also a drawback;
while the method was used against metallic and organic pollutants inside controlled laboratory conditions,
it has not been tried for metallic pollutants outside of them (Glick 2010). This is worrisome, because metallic
pollutants are far more harmful to the soil than organic ones. Another unfortunate
bit; some of the plants could not produce enough biomass inside these controlled conditions to be considered efficient in
the field. Glick concludes that; 1.) “obstacles” in the experiment are
traceable, 2.) it is important to address problems of metal bioavailability in
contaminated soils, and 3.) to use phytoremediation, assisted by bacteria, on a
larger scaled environment of organic and/or metal pollutants. All which will require a better understanding of
the relationship between, soils, plants, contaminants, and bacteria with each
other, as well as with phytoremediation assisted by bacteria.
Scientist researching these
alternative methods to improve soil health look very promising, but
unfortunately for them to be successful, and for the use in chemicals to be
reduced, soil’s relationship with plants needs to be understood. This is
because it will be beneficial in the long run, both health wise and
economically.
Sources:
Arnhold, Tilo. "Fertile soil doesn't fall from the sky.
The contribution of bacterial remnants to soil fertility has been
underestimated until now." Research for Environment. Hermholtz
Centre for Environmental Research-UFZ, 14 Dec 2012. Web. 29 May 2013.
<http://www.ufz.de/index.php?en=31184>.
Coombs, Amy. "Fighting Microbes with Microbes." Scientist.
1 Jan 2013: n. page. Web. 29 May. 2013.
<http://www.the-scientist.com/?articles.view/articleNo/33703/title/Fighting-Microbes-with-Microbes/>.
Glick, Bernard R. "Using soil bacteria to facilitate
phytoremediation." Biotechnology Advances. 28.3 (2010): 367–374.
Web. 29 May. 2013.
<http://www.sciencedirect.com/science/article/pii/S0734975010000212>.
Mishra, Upasana, and Dolly Wattal Dahr. "Biodiversity
and Biological Degradation of Soil." Resonance. (2004): n. page.
Web. 29 May. 2013.
<http://www.ias.ac.in/resonance/Jan2004/pdf/Jan2004p26-33.pdf>.
Richardson,
Allan E., , et al. "Plant
and microbial strategies to improve the phosphorus efficiency of
agriculture." International Journal on Plant-Soil Relationships.
(2011): n. page. Web. 29 May. 2013.
<http://link.springer.com/article/10.1007/s11104-011-0950-4/fulltext.html>.
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