With regular use of biofertilizers (new microbial inoculum) to soil,the new microbial species may get established in the agricultural farm soil.Over time it may compete and dominate over the native species.So some scientists question the need for repeated or continuous use of biofertilizers in the same field.As I understand there may be change/alteration in microbial genome in the soil.I think learned microbiologists may give more comprehensive and authentic information on this aspect.
When a microorganism introduced in an ecosystem, the living organisms interact with each other for their survival. Inter-specific and intra-specific interactions among microorganisms may be positive or negative either for one partner or both. Microbe-microbe interactions carry out many ecologically significant processes. The interaction may be Mutalism ( two organisms of different species are mutually benefited); Co-operation (two organisms within a species are mutually benefited); Commensalism (one organism benefits from others without affecting the growth and activity of the later); parasitism (one species benefits at the expense of others) etc. Beside this, there are plant-microbe interaction (eg.legume-rhizobia) faunal-microbial interaction (may be mutalistic or antigonistic associations). So, there is always a ecological risk if organisms are not choose properly. Moreover, carbon demand is another factor which has to be taken into account when we are introducing any organisms into the system.
Another face of introducing microbes in the field is the genetic interaction with native microbes and very fair chances of HGT between related or unrelated microbes. Such interactions and genetic transfer may be beneficial or not and can give rise to potential risk to the native population of microbes that over the years adapted for better survival.
thank you for your answers,
Is it possible that occur conjugation or transformations or transduction between microorganism that we add as biofertilizers and other microorganism in farm? what is risk of this ?
Yes, conjugation, amensalism, transformations or transduction is possible. Further inter-specific competition and antagonism is also reported.
Another risk is that if biofertilizers have not been properly characterized other than their PGP activities, there are chances that they may also carry traits of pathogenic, toxicity. Generally we look for PGP activities only and do not characterized fully up to evolutionary phylogenies . There are many bacteria of group Enterobacter, Mycobacterium, Burkholderia cepacia, B. vietnamese etc possess strong PGP activities such as PO4 solubilization, IAA production other than their phytopathogenic and human pathogenic traits.
I think , our colleagues have already very ably provided some insightful responses , worth reading all of them..This is a very apt question . Like any other biological system , there is an evolutionary process of microbiome to reorient their diversity in response to stimuli received either from within own ecosystem or in response to climate ( they could be seasonal as well) -related stimuli..Considering such risks only , adding native isolates of microbes in a given ecosystem is invariably recommended, unless supported with thorough prior field response studies...
Let me share with you a simple incidence. In citrus , we have heavy incidence of Phytophthora causing foot and root rot diseases . However , in the same orchard , there were some plants totally devoid any symptoms , we took soil from within the rhizosphere zone of those healthy plants and put into the rhizosphere of those plants displaying Phytophthora symptoms , and withtin a year , those unhealthy plants started showing symptoms of rejuvenation . Taking clues from such responses , we now recommend , the rhizosphere soil from healthy trees alongside the mixture of organic manures and inorganic fertilizers to be applied to citrus. And , it works astonishingly so effective...
Diammonium phosphate when applied to soil will at first increase the soil pH, making it more alkaline but with subsequent addition over a long term, will decrease the pH of the soil and make it more acidic with its accompanying problems.
Dr. Anoop, I am really very happy to read by chance recommendation which has come up through your experience. But further scientific validation is needed through basic studies on type of microbes avilable in consortia and their population and interaction between them. Can we define role of each microbe in such consortia. Is their possibility to further isolate and make pure culture and further mixing together and commercialze them.
one of the risk is :
when we use biofertilizers in farms, this microorganism may go to lakes and go into fish gut and cause bacteremia or any other diseases....
That could happen even in absence of biofertilization as well....
I think the addition of specific microorganisms as bio fertilizers could affect the population of microorganisms species and quantity ,as well as this addition should affect the availability of nutrients,pH and the nutritional relations in root zone,THe plant species may play role in this new case.
Dr.Srivastava you right but when we add Non-native microorganism this could cause diseases more than native ones.... So, our scientific group use native microorganism as biofertilizers...
Then, where do these biofertilizer companies pour their microbial products, they are non-native micorbes only ..In principle , we should always use native microbes ..
Dear Mostafa Armandeh, I think the addition of microorganisms like Rhizobia, Mycorrhiza, or any other benificial microorganisms are essential to treat the soil insted of using chemicals. But, the benificial microorganisms must isolated from the same location and propagated in order not to introduce a new species to the location, and to establish the microbial balance in the natural ecosystem.
Dr.Malhotra, for your and other colleagues information , I wish to state that in soil biodiversity and biofertilizers network project ,ICAR several microbial consortia have been developed and are being tested in the last one decade or more.The commercial use of these cultures did not gain sufficient ground. Efficient microbial cultures are usually isolated in local or regional environments/ soils but they can be used locally or nationally.One has to test the biocultures for their pathogenic straits.As I understand the genome of introduced organism undergoes change and will be adopted to local conditions with time.
We have no seen any harmful effect of added biofertilizers in rice.
Why do you think adding more of the same resident microorganism is going to drive significant change beyond perhaps a limited temporary effect? Can you offer citation ?
In any case, suggest a data-based risk assessment be performed for whatever inoculum you propose - whether native or new - and that control your decision.
adding microorganism as biofertlizers can change soil genome via various ways such as transduction, transformation and etc.... using biofertilizers without sight of Ecological view = it is one the ecological risks to environment
Introduction of microbes in any ecosystem is done for certain purpose which may be nutrient supplementation, bioremediation or any other ecosystem service. In fact all kinds of microbes exist in soil but to express their potential, it has to compete with other inhabiting groups. introduction of microbes through biofertilizer ensures the numerical dominance of a particular species to offer benefit. certainly it will alter the actual microbial composition of the soil but the effect is probably transient and that's why we need to apply biofertilizers in every season. The native microflora tend to competitively eliminate the introduced one since they are more fit to that soil condition.
Yes Dr Subba Rao, you have rightly mentioned that genome of introduced organism undergoes change and will be adopted to local conditions with time. But it is also good to have native and efficient isolates.
I appreciate the answer of my junior colleague Dr.Jyoti Thakur.As I understand some questions are not fully answered in biofertilizers use in agriculture.Is it required to inoculate the soil every year in all soil conditions ?Or we need to apply biofertilizers every year in soils or climates where sufficient population of the introduced efficient organism does not exist?. When new leguminous crop (like soyabean in central India) is introduced where existing N fixer is not there,an external bioculture is introduced.With time in a few / several decades the introduced organism genome undergoes change and is adopted to the new environment.I do not think that the adopted microbe continue to face competition from native related species.As mentioned by colleagues,even the genomics of native organism may change.So practically there may not be any difference between the native and introduced and adopted organism.I request colleagues to provide references in this line.
Dr Rao,
Thanks for your comments. In one of my study tagged inoculated bacteria in rice rhizosphere decreased very sharply after about 30 days of inoculation. The fact might be that the bacterium was isolated from legume host.
Thanks for your comments....
I concluded that isolate native bacteria as biofertilizer is recommended because it can adapt coditions and have lower ecological risk to ecosystem
Is there any study anywhere , where inoculation of microbes in a soil disturbed the native microbial diversity..?9?
The addition of bio fertilizers surely affect the balance between organisms lived in the rhizosphere zone ,and new relations could be started between these microbes and the native species .This addition may be led to positive or negative effects on the ecosystem .
This is the reason , we need a comprehensive study including toxicological studies to declare a microbe having beneficial effects on crop response...
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