SUBSTRATE INDUCED GROWTH
RESPONSE OF SOIL AND
RHIZOSPHERE MICROBIAL
COMMUNITIES UNDER ELEVATED CO2
S.А. Blagodatsky, Е.V. Blagodatskaya, E.G. Demyanova,
V.N. Kudeyarov
Institute of Physicochemical and Biological Problems in Soil Science,
Pushchino, Russia
Т.-H. Аnderson, H.-J. Weigel
Institute of Agroecology (FAL), Braunschweig, Germany
September 30, 2005
ICDC7 Boulder, Colorado
Overview
 Introduction
 Experimental
design and methods
 Soil Microbial Biomass measured by
SIR and dsDNA
 Kinetic characteristics of substrateinduced growth response on glucose
 Discussion and conclusions
September 30, 2005
ICDC7 Boulder, Colorado
Motivation: why it is necessary
to study ?


Soil microbial biomass and activity are key
factors controlling C-turnover in soil and
respectively acceleration/mitigation of the
resultant CO2 flux from soil to atmosphere
in response to proposed increase of C
input to soil in elevated CO2 world
Contradictory effect of elevated CO2 on
soil microbial biomass: some studies show
positive response and some show no
response or even negative
September 30, 2005
ICDC7 Boulder, Colorado
What could help:


Accounting for other important factors:
soil N level, type of growing plant, soil
moisture content, dynamic nature of
observed effects, spatial distinction
between bare soil and rhizosphere
More careful consideration of functional
properties and structure of soil microbial
community
September 30, 2005
ICDC7 Boulder, Colorado
Hypotheses
 Elevated
CO2 effects growth
characteristics of soil and
rhizosphere microbial communities
Aim
 to
study the effect of elevated
concentration of atmospheric CO2 on
biomass and specific growth rates of
microbial communities of soil and
rhizosphere
September 30, 2005
ICDC7 Boulder, Colorado
Biosphere 2 Center, Arizona,
USA


ambient (400 ppm) and elevated (800 or 1200
ppm) atmospheric CO2 concentrations
Cottonwood tree (Populus deltoides)
September 30, 2005
ICDC7 Boulder, Colorado
Free Air Carbon Dioxide Enrichment
(FACE) Braunschweig, Germany



ambient (350-370 ppm) and elevated (550 ppm)
atmospheric CO2 concentrations
N fertilization at rates 126 and 63 kg·ha-1·year-1
Sampling: 2001 - sugar beet,
2002 and 2005 – winter wheat
September 30, 2005
ICDC7 Boulder, Colorado
Measured characteristics:
 Soil
microbial biomass – SIR method
 Soil
dsDNA –
(Anderson, Domsch, 1978)
direct extraction and
measurement of fluorescence after dyeing with
Picogreen (Marstorp, Witter, 1999; Blagodatskaya
et al., 2004)
 Kinetic
parameters of substrateinduced growth response of soil
microorganisms, total and active
microbial biomass by SIGR method –
fitting the data on respiration rates measured
after soil amendment with glucose + NPK and/or
yeast extracts (Panikov et al., 1991; Blagodatsky
et al., 2000)
September 30, 2005
ICDC7 Boulder, Colorado
Basic principle of SIGR method
(Panikov et al., 1991)
CO2 evolution rate after substrate
amendment ( ):
v(t) = A + B * exp(m*t) , where
A – initial rate of uncoupled (non-growth)
respiration
B – initial rate of coupled (growth) respiration
m – Maximal specific growth rate
t - time
September 30, 2005
ICDC7 Boulder, Colorado
Calculation of active and total
microbial biomass based on SIGR
Active microbial biomass:
X’ = B / m
 Total microbial biomass:
X = X’ * r0, where
r0 – activity status calculated from
the ratio between A and B

September 30, 2005
ICDC7 Boulder, Colorado
Soil microbial biomass in intensive
agroforestry biome of Biosphere 2 Center
900
Microbial biomass (SIR)
800
600
 g C *g soil
-1
700
500
Rhizosphere
Bare soil
400
300
Please, see
also poster
HI-396 by
Kudeyarov
et al.
200
100
0
400ppm
September 30, 2005
ICDC7 Boulder, Colorado
800ppm
CO2 concentration in atmosphere
1200ppm
400
Microbial biomass
350
Ambient CO2,
rhizosphere
µg C*g
-1
300
Elevated CO2,
rhizosphere
250
200
Ambient CO2,
soil
150
100
Elevated CO2,
soil
50
0
100% N
90
50% N
dsDNA in soil
80
70
µg*g
-1
60

Rhizosphere
effect on
microbial
biomass (SIR)
and dsDNA in
soil under sugar
beets grown at
different
atmospheric CO2
concentrations
50
40
30
20
10
0
Increase in microbial biomass (SIR) under
elevated CO2 was only transient and was
September
30,
2005
not
supported
by data on dsDNA content
ICDC7 Boulder, Colorado

100% N
50% N
Atmospheric CO2 effect on SIGR:
soil under cottonwood tree (Populus
deltoides)
-1 -1
 g C-CO2 *g *h
150
Respiration rate
400 ppm
CO2 conc.
800 ppm
400ppm
1200 ppm
800ppm
100
1200ppm
50
max
0.30 ±
0.01
0.39 ±
0.04
0.47 ±
0.06
hours
0
0
September 30, 2005
ICDC7 Boulder, Colorado
5
10
15
20
Atmospheric CO2 effect on SIGR:
soil under sugar beets
100
µg С-СО 2*h -1*g -1
µg С-СО 2 *h-1 *g -1
100
Rhizosphere, 100% N
50
hours
0
50
hours
0
0
5
10
15
20
25
0
5
10
15
20
25
100
µg С-СО 2 *h -1 *g -1
100
µg С-СО 2 *h -1 *g -1
Soil, 100% N
Rhizosphere, 50% N
50
hours
0
Soil, 50% N
50
hours
0
0
5
10
September 30, 2005
ICDC7 Boulder, Colorado
15
20
25
0
Elevated CO2
5
10
15
20
25
Ambient CO2
Atmospheric CO2 effect on SIGR:
soil under winter wheat - 2002
µg С-СО 2 *h -1 *g -1
Rhizosphere, 100% N
50
hours
µg С-СО 2 *h -1 *g -1
100
100
0
50
hours
0
0
5
10
15
20
25
0
30
100
µg С-СО 2 *h -1 *g -1
100
µg С-СО 2 *h-1 *g -1
Soil, 100% N
Rhizosphere, 50% N
50
hours
0
0
5
10
September 30, 2005
ICDC7 Boulder, Colorado
15
20
25
5
10
15
20
25
30
Soil, 50% N
50
hours
0
30
0
5
Elevated CO2
10
15
20
25
30
Ambient CO2
Atmospheric CO2 effect on SIGR:
soil under winter wheat - 2005
100
100
-1
Soil, 100% N
75
-1
75
C-CO2, g g h
C-CO2, g g-1 h-1
Rhizosphere, 100% N
50
25
hours
50
25
hours
0
0
0
5
10
15
20
25
30
35
0
100
5
15
20
25
30
35
100
Rhizosphere, 50% N
Soil, 50% N
C-CO2, g g-1 h-1
C-CO2, g g-1 h-1
10
75
50
25
hours
0
0
5
10
15
September 30, 2005
ICDC7 Boulder, Colorado
20
25
30
35
75
50
25
hours
0
0
5
Elevated CO2
10
15
20
25
30
Ambient CO2
35
Rest
4%
CO2*N*Rhi
4%
Specific growth rate 
N
16%
CO2,
57%
12%
Rhi
6%
CO2*Rhi
Total microbial biomass
CO2*N*Rhi
3%
Rest
11%
CO2,
26%
N
10%
48%
Rhi
Growing microbial biomass
CO2*N*Rhi
9%
Rest
12%
CO2,
24%
N
13%
11%
September
30, 2005
N*Rhi
8%
ICDC7 Boulder, Colorado
Rhi
22%
CO2*Rhi
3-way ANOVA,
Soil under sugar beets,
Contribution of
independent factors:
elevated CO2, rate of Nfertilizers and distance
from root surface on total
variation of maximal
specific growth rate of soil
microorganisms, total and
active microbial biomass
Specific growth rate, 
Rest
17%
CO2 *N*Rhi
18%
3-way ANOVA ,
CO2,
36%
N
26%
CO2*N
0%
Total microbial
biomass
CO2,
4%
Soil under winter wheat,
3%
Rhi*N
Rhi
3,9%
Rhi*N
28%
Rest
56%
CO2*N*Rhi
5,2%
Growing microbial
biomass
CO2*Rhi
2%
Rest
26%
September 30, 2005
CO2*Rhi*N
ICDC7
Boulder, Colorado
24%
N
2%
Rhi
10%
N
5%
CO2*N
31%
Contribution of
independent factors:
elevated CO2, rate of Nfertilizers and distance
from root surface on total
variation of maximal
specific growth rate of
soil microorganisms,
total and active microbial
biomass
Effect of CO2 enrichment on
microbial turnover in soil
Human activities
CO2
Photosynthesis
Respiration
Exudation
September 30, 2005
ICDC7 Boulder, Colorado
Humification
Shift to r-strategy
Critical question for warming
potential acceleration / mitigation
 How
will change the ratio
respiration/humification after
changing of atmospheric CO2
concentration ?
Further studies combining kinetic
approach with C and N labeling are
needed
September 30, 2005
ICDC7 Boulder, Colorado
Conclusions
 Elevated
CO2 affects the functional
structure of soil microbial community
 The
size of active/total soil microbial
biomass depends on elevated CO2 in
a lesser extent
 Specific
growth rate (µm) – the most
sensitive parameter reflecting
changes in ecological strategy of
microbial communities
September 30, 2005
ICDC7 Boulder, Colorado
Thank you for attention!
ACKNOWLEDGEMENTS
•Research was supported by BMVEL, DAAD and
Russian Foundation for Basic Research
•Sponsorship of ICDC7 supporting agencies and
decision of Scientific Committee enabled participation
of first author in conference
September 30, 2005
•Special
ICDC7 Boulder,
Coloradothanks to Karl Bil’ - Biosphere 2 Center