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Plants & Soil, Bulletin No. 1

David B. Hedrick davidbhedrick at icx.net
Thu Jun 5 14:19:45 EST 1997

Some general hypotheses:

>         1) bacterial survival and growth on plant surfaces and in the soil,

Microbial biomass in soil is positively correlated with organic carbon,
surface area, and water availability.  

Most of the time, most of the microbiota are not active, but just
hanging on until the next meal.  Disturbances such as physical
disturbance, wetting, or addition of a nutrient will give a (short?)
peak of activity by those able to take advantage of it.  

The soil community includes the professional starvers (oligotrophs), the
low-activity specialists (methanotrophs, nitrogen metabolizers, etc),
weeds (exploiting transient resources), preditors, and aliens
(allochthonous microbiota).  

>         2) the diversity of the microbial communities in these environments and

I would love to make guesses about what would affect microbial diversity
in soils, but I don't think at this point we have good methods to
measure microbial diversity.  DNA-DNA re-association is attractive, but
very difficult and time-consuming from what I have heard.  DNA probes
only detect what is probed for, and no one has enough probes to give
representative coverage of the microbiota in a gram of soil.  Plate
culturing will only see 1% - 0.1% of the community.  

Diversity itself is a problematic and contentious concept.  I once tried
to publish a short paper on diversity, and was handed my head for my
trouble.  I think this is very important question, and would like to see
more discussion on the measurement of diversity before we go very far on
what affects it.  Also, it is more important to get a useable method,
and solve the theoretical problems later.  

>         3) the bacteria-plant interaction.

The microbial communities in cultivated soils are smaller and different
than those in uncultivated or no-till soils.  Does cultivation affect
soil physical properties and/or compostion, which then affects the
microbiota, or does it have a more direct affect on the microbiota?  

There are 2 shapes to the volume of soil microbiota affected by plant
roots - solid and fractal.  A solid affected soil volume shape results
from a dense penetration of the soil by plant roots, such as under a
grass tussock.  A fractal affected soil volume shape results from a more
sparse and exploratory penetration of the soil, such as by an oak.  

Soil is a fractal.  The distribution of microbial biomass will also be a

I hope I have said something provocative enough to engender discussion.  

Technical writing, literature search, and data analysis at the interface
of chemistry and biology. 

	davidbhedrick at icx.com

	David B. Hedrick
	P.O. Box 16082
	Knoxville, TN 37996

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