(Forwarded) RE: Diaz et al, (nature 12/8): (Fol

EWEN at uk.ac.uel.whmain EWEN at uk.ac.uel.whmain
Wed Sep 1 06:21:42 EST 1993


Forwarded message:
From:     Self <WHMAIN/EWEN>
To:       "bionet.plants newsgroup" bionet-news at daresbury.ac.uk
Subject:  RE: Diaz et al, (nature 12/8): (Follows What do we want...)
Date:     1 Sep 93 11:15:36

Greetings Plantnetters.

As my last posting to the newsgroup seems to have gone astray
somewhere (at least, I hope Tony Didn't bin it), I'm going to try
again.

RE: Diaz et al (Nature 12th August). I'm the et al, as I did the
microbial analysis part of the project.

Richard Winder (Forestry Canada) asks how the nutrient limitations to
CO2-induced productivity occur even in good soils, due to blooming
microflora which uptake substrates from non-mycorrhizal plants willl
impact global warming models.

OK, I had a hand in this paper and I must confess that I had to sit
down and read it slowly too. But, basically, this is what we think
happens;-

1: Increase in CO2 causes, in plants, accumulation of non-structural
carbohydrate, or, as I understand it, starch vesicles in leaves. When
the plant has reached maximum, if you like, carrying capacity for
these storgae carbohydrates, the amount of carbohydrate contained in
the root exudate increases, which causes a flush of rhizosphere micro-
organisms. The demand for nutrients by the rhizosphere micro-
organisms may (I stress MAY) then cause a nutrient deficiency in the
plant. We base this conclusion on the increase in Microbial Carbon
and Nitrogen, and the appearance of N-deficiency syndrome in the
leaves of the plants.

2: This N-deficiency wasn't seen in mycorrhizal species. Although we
didn't actually look at the mycorrhorhizae themselves (they're still
all sitting in my freezer waiting for me to get a few free moments),
what we suspect happens is this: As we didn't see deficiency
syndromes in the mycorrhizal species, that the mycorrhizal sheaths
were in fact "controlling" the outflow of root exudate, either
utilizing it themselves (which would make them "out-compete" the free-
living species, make them more successful therefore at the
assimilation of nutrients and), therefore, in effect, the increased
CO2 would therefore favour the mycorrhizal species, or even
(possibly) infectivity rates or, if you like, receptivity to
infection.

Now, as to what this would actually do to a global warming model ?
Pass. I'm just a poor bacteriologist floundering marginally out of my
depth in the big world of Big Models, trying to do my own Strategy
Model for C:N:P:K flow through the soil rhizosphere . However, ask my
opinion and you'll get it, and it is that;-

What you have to remember is that this experiment dealt with levels
of atmospheric CO2 that are twice Normal. Now, as far as I read it,
this would probably mean that Humanity wouldn't be around to witness
the effects. However, if this is a trend that will show in ppb
increases in CO2, or even less, it could be quite interesting in that
what we may see is a species shift, both in plants and soil
micro-organisms, towards a) mycorrhizal species (so that the number
of communites containing mycorrhizal species will increase both in
number and diversity) and b) free-living rhizosphere organisms may
decrease in diversity as less plant-derived nutrient becomes
available and the species become more specialised, possibly tending
towards the utilisation of less readily available forms of carbon.

So tell me I'm talking bull ? I don't really know one way or the
other. My interest in this experiment was purely technical, i.e. I
did all of the assays, a few of which Sandra didn't want to put in
the paper, such as Microbial activity and Biomass by lipid Phosphate,
both of which showed some rather interesting results,and that I may
try playing with at more depth when I get my own model up and running.

As usual, happy to discuss. You know where to get me....

EWEN


***************************************************
*         "Beam Me Up, Scotty,                    *
*               This Planet Sucks !"              *
***************************************************
* Ewen McPherson, Research Assistant              *
* e-Mail: EWEN at whmain.uel.ac.uk                   *
* Snail : Environment and Industry Research Unit  *
*         Department of Environmental Sciences    *
*         University of East London               *
*         Romford Road, Stratford,                *
*         London E15 4LZ                          *
*         United Kingdom                          *
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