"Soil is a young substance."
- Peter Farb -
We walk on the surface of the Earth every day but hardly wonder how come the soil was born. To boot, our feet are insulated from the contact with the bare soil given our urban lifestyle. So, naturally we do not give a second thought to the soil under our feet except while washing it off our feet after an outing; leave alone the invisibile colony of organisms that inhabit the soil and their feedback loop in the eco-systemic services.
Nature's weathering and earthquakes. Rocks splinter. Roll down, crash and break down into pieces. After millenia of action, tiny worn out fragments settle down. Microscopic in dimension. A mantel of smooth iotaic layer on Earth's surface still is not soil! For 3/4rth's of geologic time there was no soil on Earth. 'There is no soil without life', wrote Peter Farb.
How did first life get into the soil? In ancient times, spores ought to have held tight after a tidal wash onto the skeletons of the soil nudging deeper nibbling or gobbling the micronutrients lodged between minuscule crevices leading to the first conversion of particle minerals into true soil - transmorphing soil into a nursery bed for life. Weathering gave pottasium and phosphorus - two vital ingredients for plant growth. But, nitrogen - though relatively abundant in the atmosphere - did not exist on the parent rock material! So, how did the soil obtain its first repository of nitrogen?
Was it lightning or microbes? Scientists debated for years till around 1890 when Ukranian-Russian Sergei Winogradsky, a brilliant cum perservering soil biologist, established the fact that microbes fixed nitrogen in the soil. His method demonstrated that some microbes can take nitrogen from the atmosphere and convert it into nitrogen compounds. He was hunting for organisms that manufactured nitrogen compounds on their own in the absence of those nitrogen compounds. So, as chief of the division of general microbiology of the Institute of Experimental Medicine, he identified the obligate anaerobe Clostridium pasteurianum. He prepared arrays of cultural dishes containing every nutrient for growth except nitrogen. He added pinches of soil to the dishes and soon nitrogen got fixed. Only three kinds of bacteria survived this starvation diet but they were interlocked together that Winogradsky was not able to find out which of the three bacteria or whether all three fixed nitrogen. After a disheartening series of experiments, Winogradsky managed to separate the three bacteria "but now none of them - if grown alone - could fix nitrogen," wrote Peter Farb. But when Winogradsky combined the bacteria, nitrogen got fixed!
Now, Winogradsky employed a novel technique: he deprived the bacteria of all air except nitrogen. Two of the bacteria died and the third bacterium - Clostridium - thrived. Clostridium thrived only because it was an anaerobe - a bacterium that only functions in the absence of oxygen. Yet it begged an answer as to how it managed to separate nitrogen when the air itself is over 1/5th part oxygen? "Here was explained the two interlocking bacteria: they insulate Clostridium against the atmosphere, themselves absorbing the oxygen and leaving only nitrogen!" explains ecologist Peter Farb.
Winogradsky went on to prove much about the nitrogen bacteria in the soil, and so thorough was his work that "after nearly 70 years little new information has been added," observed Farb in 1963. Now we know that actually very few free-living bacteria are able to convert atmospheric nitrogen, but that it is a very common trait among the blue-green algae. Yeasts and fungi too have joined the nitrogen-fixers' club.
Today the free-living bacteria fix but small amounts of nitrogen found in the soil; most of the repository of nitrogen compounds comes from other bacteria which live on the roots of certain plants and are called legume bacteria. But the free-living nitrogen bacteria, or forms with a similar ability, were perhaps among the first inhabitors of the earth when the seas receded, writes Farb, 'for they would have had to build up vast amounts of nitrogen in the soil before other forms of life could gain a foothold.'
"It will no doubt always remain an unsolved problem, for no record of this event has been left to us," wrote Peter Farb in his 1953 classic Living Earth; and undoubtedly, questions continue to linger at subtler levels even as soil chemistry has advanced a great deal in the intervening year. Winogradsky is best known for discovering chemoautotrophy, which soon became popularly known as chemosynthesis, the process by which organisms derive energy from a number of different inorganic compounds and obtain carbon in the form of carbon dioxide.
Sergei Winogradsky also was the microbiologist who pioneered the cycle of life concept. He discovered the first known form of lithotrophy during his research with Beggiatoa (bacteria that relish life in sulfur-rich environment) in 1887. He reported that Beggiatoa oxidized hydrogen sulfide (H2S) as an energy source and formed intracellular sulfur droplets. This research provided the first example of lithotrophy, but not autorophy. His research on nitrifying bacteria would report the first known form of chemoautotrophy, showing how a lithotroph fixes carbon dioxide (CO2) to make organic compounds. The Winogradsky column - a simple device for culturing a large diversity of microorganisms - remains an important display of chemoautotrophy and microbial ecology demonstrated in microbilogy lectures around the world./
- Peter Farb -
Nature's weathering and earthquakes. Rocks splinter. Roll down, crash and break down into pieces. After millenia of action, tiny worn out fragments settle down. Microscopic in dimension. A mantel of smooth iotaic layer on Earth's surface still is not soil! For 3/4rth's of geologic time there was no soil on Earth. 'There is no soil without life', wrote Peter Farb.
How did first life get into the soil? In ancient times, spores ought to have held tight after a tidal wash onto the skeletons of the soil nudging deeper nibbling or gobbling the micronutrients lodged between minuscule crevices leading to the first conversion of particle minerals into true soil - transmorphing soil into a nursery bed for life. Weathering gave pottasium and phosphorus - two vital ingredients for plant growth. But, nitrogen - though relatively abundant in the atmosphere - did not exist on the parent rock material! So, how did the soil obtain its first repository of nitrogen?
Was it lightning or microbes? Scientists debated for years till around 1890 when Ukranian-Russian Sergei Winogradsky, a brilliant cum perservering soil biologist, established the fact that microbes fixed nitrogen in the soil. His method demonstrated that some microbes can take nitrogen from the atmosphere and convert it into nitrogen compounds. He was hunting for organisms that manufactured nitrogen compounds on their own in the absence of those nitrogen compounds. So, as chief of the division of general microbiology of the Institute of Experimental Medicine, he identified the obligate anaerobe Clostridium pasteurianum. He prepared arrays of cultural dishes containing every nutrient for growth except nitrogen. He added pinches of soil to the dishes and soon nitrogen got fixed. Only three kinds of bacteria survived this starvation diet but they were interlocked together that Winogradsky was not able to find out which of the three bacteria or whether all three fixed nitrogen. After a disheartening series of experiments, Winogradsky managed to separate the three bacteria "but now none of them - if grown alone - could fix nitrogen," wrote Peter Farb. But when Winogradsky combined the bacteria, nitrogen got fixed!
Now, Winogradsky employed a novel technique: he deprived the bacteria of all air except nitrogen. Two of the bacteria died and the third bacterium - Clostridium - thrived. Clostridium thrived only because it was an anaerobe - a bacterium that only functions in the absence of oxygen. Yet it begged an answer as to how it managed to separate nitrogen when the air itself is over 1/5th part oxygen? "Here was explained the two interlocking bacteria: they insulate Clostridium against the atmosphere, themselves absorbing the oxygen and leaving only nitrogen!" explains ecologist Peter Farb.
Winogradsky went on to prove much about the nitrogen bacteria in the soil, and so thorough was his work that "after nearly 70 years little new information has been added," observed Farb in 1963. Now we know that actually very few free-living bacteria are able to convert atmospheric nitrogen, but that it is a very common trait among the blue-green algae. Yeasts and fungi too have joined the nitrogen-fixers' club.
Today the free-living bacteria fix but small amounts of nitrogen found in the soil; most of the repository of nitrogen compounds comes from other bacteria which live on the roots of certain plants and are called legume bacteria. But the free-living nitrogen bacteria, or forms with a similar ability, were perhaps among the first inhabitors of the earth when the seas receded, writes Farb, 'for they would have had to build up vast amounts of nitrogen in the soil before other forms of life could gain a foothold.'
"It will no doubt always remain an unsolved problem, for no record of this event has been left to us," wrote Peter Farb in his 1953 classic Living Earth; and undoubtedly, questions continue to linger at subtler levels even as soil chemistry has advanced a great deal in the intervening year. Winogradsky is best known for discovering chemoautotrophy, which soon became popularly known as chemosynthesis, the process by which organisms derive energy from a number of different inorganic compounds and obtain carbon in the form of carbon dioxide.
Sergei Winogradsky also was the microbiologist who pioneered the cycle of life concept. He discovered the first known form of lithotrophy during his research with Beggiatoa (bacteria that relish life in sulfur-rich environment) in 1887. He reported that Beggiatoa oxidized hydrogen sulfide (H2S) as an energy source and formed intracellular sulfur droplets. This research provided the first example of lithotrophy, but not autorophy. His research on nitrifying bacteria would report the first known form of chemoautotrophy, showing how a lithotroph fixes carbon dioxide (CO2) to make organic compounds. The Winogradsky column - a simple device for culturing a large diversity of microorganisms - remains an important display of chemoautotrophy and microbial ecology demonstrated in microbilogy lectures around the world./
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