cereal nitrogen fixation

EWEN at WHMAIN.uel.ac.uk EWEN at WHMAIN.uel.ac.uk
Wed Feb 3 03:42:41 EST 1993


Greetings Plant People,

On 2nd Feb, Euan Taylor from Manitoba wrote...

>A second question, relating to a naive (very) ex[eriment we did some
>time ago.
>If you plant surface sterilised seeds in autoclaved soil, growth is
>about
>1 1/2 weeks behind that of regular seeds in regular soil. What do you
>think I could be driving off in the soil tthat might cause this (NH4,
>oxygen, ?) we didn't do the other combinations at the time, as I say
>it
>was a very naive experiment that we set up last thing before
>christmas, jsut out of interest.


Now, call ME naieve, and everybody out there please feel free to
shoot me down, but can we for a moment consider 3 little words about
which my PhD revolves...

                    SOIL MICROBIAL BIOMASS

Now, looking at this experiment from the viewpoint of a
microbiologist gone soils, autoclaving the soil will kill off the
soil microbial biomass, and, more specifically in regards to Euan's
experiment, those portions of the SMB  that could prove to be
beneficial to a germinating plant (N-fixers, possibly symbionts,
possibly mycorrhizae)

Autoclaving is going to kill off 99.9% of the SMB, releasing a flush
of nutrients into the soil. What I have observed happens in this
situation is that there is, within a period of 2-3 days, a massive
recovery of the SMB from the spore bank and those portions of fungal
hyphae that have managed to survive the autoclaving. These then
utilise the nutrient made available from the kill-off, but as the
community grows, it then steps into a period of competition, both
within the SMB and with anything else in the soil (viz, Euan's
germinating plant), for resources that are becoming increasingly
unavailable (i.e. specifically P), which leads to the establishment
of a fairly aggressive community (bugs switch resources to production
of antimicrobial compounds) that may also have an effect on this poor
little seedling.

Now, I have observed this peaking/killoff of the SMB over a period of
60 days in an artificial soil (50% clay, 40% sharp sand, 10% sterile
Organic matter), and, whilst I'm still chewing the data, would be
willing to suggest that what is happening is more or less as I have
outlined it above.

How to put this politely... Listen all you plant people out there.
The processes do not start proceed and end with your little green
things. The Soil Microbial Biomass is the eye of the needle through
which the processes of plant nutrition must pass (both ways, I know,
since root exudates form a vital part of the nutrient supply for the
rhizosphere Micro-organisms).

For  great examples of how to completely ignore the SMB in plant
microcosm work, please feel free to mail me. I have a very long list.

So, let's have it people. All criticism gratefully recieved, because,
as Euan's sig file says, My institution doesn't know I exist either !
(Incidentally, great name, Euan. Not too many of us about !)

And I'ld be very grateful just to see how many other people out there
are working in similar fields to myself. The Title of the thesis is
"The application of Plant Strategist Theory to the processes of Soil
Microbial Ecology". All correspondance gratefully recieved and
replied to !

All the best,

EWEN







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*         "Beam Me Up, Scotty,                    *
*               This Planet Sucks !"              *
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* Ewen McPherson, Research Assistant              *
* e-Mail: EWEN at whmain.uel.ac.uk                   *
* Snail : Environment and Industry Research Unit  *
*         Department of Environmental Sciences    *
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