[compost_tea] Plant Succession in Relation to Bacterial & Fungal Dominance

From: Steve Diver <steved_at_ncat.org>
Date: Thu, 29 Jul 2004 19:10:16 -0000
This summary on plant succession in relation to bacterial
& fungal dominance deserves its own spot in the web
archives.  Thanks, Elaine!

--- In compost_tea_at_yahoogroups.com, soilfoodweb@a... wrote:
> Hi John -
>
> There appears to be a strong correlation with sucessional stage,
based on the over 100,000 soil samples that we've looked at. That is
what I base these conclusions on - we have looked at over 100,000
samples of soil, where the following conclusions hold.
>
> If a plant is an early, weedy species, found in grasslands, in
annual or bi-annual conditions, in areas that are typically highly
disturbed, then those are usually bacterial-dominated plants. 
>
> If plants are typically found in perennial, not-disturbed
environments, then they are typically fungal-dominated plants.
>
> The earliest colonizers in both categories (annual versus perennial)
require high levels of inorganic nitrogen to germinate and maintain
dominance.  Thus, inorganic fertilizers will select for these weedy
species in both situations.  Reduce the available inorganic N levels,
and these weedy species do not thrive.  Your later successional plants
do better in conditions where inorganic nitrogen is a limited pool in
the soil. 
>
> So think of succession - which plants are earliest in the
colonization process of ecosystem successional cycles?  These are the
weedy species, and they are highly bacterial dominated around the
roots.  Later successional plant species will be less bacterial
dominated, and require more fungi in the balance.  More fungi to
suppress disease, to alter pH to result in potentially a less strongly
alkaline condition.  The most productive grassland situations are
balanced, one to one fungal to bacterial biomass. 
>
> Remember, we measure biomass, and thus fungi and bacteria can be
compared.  Please realize this when you hear the recent criticisms
from ag scientists who are saying bacteria and fungi can't be
compared.  If we assess biomass, then bacterial biomass and fingal
biomass can be compared.  If you assess numbers, then it is correct
that bacterial numbers and fungal numbers are a silly thing to
compare.  But my conclusions are based on biomass, not numbers.
>
> As you move into forested situations, and into HEALTHY forest soils,
the soil becomes fungal dominated.  The most productive forests are
highly fungal.  Perhaps 1000 time more fungi than bacteria in healthy
old growth forest soil.  But bacterial biomass is highest of any
ecosystem in these old growth forests.  It's just that fungal biomass
is much, much higher. 
>
> So, those scientists critsizing me, saying that what I say is
"nonsense" because thye are showing that bacterial counts are highest
in old growth forests just aren't listening to what I say.  At least
they are starting to pay attention to organisms in soil, but plate
count methods of assessing NUMBERS of bacteria are fungi are just
silly.  So many wrong conclusions have been based on that kind of
assessment. 
>
> Soil pH correlates with all this.  Highly bacterial soil tends to be
very alkaline, while highly fungal-dominated soil tends to be in the
5.5 to 6.5 range. 
>
> But you have to pay attention to compaction, becuase if the soil
compacts and goes anaerobic, then soil pH will drop, and can become
VERY acidic.  Highly acid soils are indicative of very sick
conditions.  The ecosystem may well be going "backwards" towards more
backterial conditions.  Acid soils will become alkaline once the
anaerobic conditions are alleviated, but that may take thousands of
years to shift.  Or only a decade.  The environmental conditions must
be paid attention to. 
>
> But then consider that when we talk about wetland, or riparian
systems, things are different.  Soils that are water-logged for some
part of the year tend to have lower pH, because there may be anaerobic
dconditions during water-logged times.  Anaerobic bacteria produce
VERY alkaline metabolites.  How anaerobic for how long? 
>
> So, think of where your plants occur in the real world.  What is the
ecosystem, or habitat that they normally occur in?  That should give
you some good clues about what they like - bacterial, or
fungal-dominated conditions?
>
> If you have specific questions about plant requirements, just ask me
the specific plant species.  I may have to ask back, where does the
plant normally occur?  In forest, or grasslands?  In early
successional forest, or early successional grasslands?  In weed
fields, or mature grasslands?  Then we can typically answer the
question, even if we haven't measured the ratio.
>
> It is safest, however, to actually measure the ratio.......
>
> Elaine
>
> In a message dated 7/29/2004 9:05:13 AM Eastern Daylight Time,
"urbanworms" <urbanworms_at_h...> writes:
>
> >
> >Hi Elaine. A couple of  weeks ago Jeff gave a great list of fungal
vs. bac
> >dominant plants. But we will never have a complete list so I'm
looking for
> >general indicators of where a plant falls on the bac/fungal continuum.
> >
> >If we are unsure what a plant's native habitat was like, what other
factors can
> >be indicators of its microbial preferences? How about a plant's ph
> >preference? There seems to be a correlation between acid loving
plants and
> >those that thrive in fungal environments.  Is this a reliable
indicator? Are there
> >others?
> >
> >John
> >Urban Worms Recycling &
> >Green-n-Healthy Organics
> >
> >--- In compost_tea_at_yahoogroups.com, soilfoodweb@a... wrote:
> >> Good start on the ratios, Jeff!  You've been listening!  And
putting info
> >> together.  Anyone else want to continue to expand it? 
> >>
> >> Can we put the list on the list serve for people to share? 
> >>
> >> Elaine R. Ingham



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Received on Thu Jul 29 2004 - 18:12:55 EDT

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