FEC402.fm Page 108 Wednesday, March 1, 2000 5:54 PM
Functional
Ecology 2000
14, 108 – 114
Microbial processes and carbon-isotope fractionation in
tropical and temperate grassland soils
Blackwell Science, Ltd
H. ŠANTRŮČ KOVÁ,* M. I. BIRD† and J. LLOYD‡
*Institute of Soil Biology AS CR and Faculty of Biological Sciences, University of South Bohemia, Na sádkách 7,
CZ-370 05 České Budějovice, Czech Republic, †Research School of Earth Sciences, Australian National
University, Canberra, ACT 0200, Australia and ‡Max Planck Institute for Biogeochemistry, Tatzendpromenade
1a, D-07701, Jena, Germany
Summary
1. The carbon content and δ13C value of soil organic carbon (SOC), microbial biomass
(Cmic) and respired CO2 were measured in a range of grassland soils from tropical and
temperate biomes to determine if isotope effect of microbial degradation can induce
a shift in isotope composition of SOC and CO2. The soil from a depth of 0–2 cm
was analysed. Cmic was measured using the chloroform fumigation extraction method,
while CO2 was measured in a closed system after 3 and 10 days of incubation.
Two soils, temperate and tropical, were used for a long-term experiment, in which
measurements were performed after 3, 10 and 40 days of incubation.
2. SOC and Cmic decrease exponentially with increasing mean annual temperature.
Cmic decreases more slowly than SOC, resulting in a higher proportion of Cmic in the
SOC of tropical soils relative to temperate soils.
3. The δ13C value of Cmic and respired CO2 reflects gross changes in the δ13C value of
SOC in the corresponding sample. On average, Cmic is 13C-enriched by c. 2‰ compared with SOC, while respired CO2 is 13C-depleted by c. 2·2‰ compared with Cmic.
Thus, the observed 13C-enrichment in Cmic is balanced by a corresponding 13C-depletion
in respired CO2 resulting in the δ13C value of respired CO2 being approximately similar
to the δ13C of SOC.
4. The isotope effect of microbial degradation is of importance in soil. It can be
induced by selective utilization of SOC and isotope discrimination during metabolism. Metabolic isotopic discrimination is dependent on the growth stage of the soil
microbial population.
Key-words: Carbon isotopes, isotopic fractionation, microbial biomass, microbial respiration, soil organic
carbon
Functional Ecology (2000) 14, 108 – 114
Introduction
© 2000 British
Ecological Society
In the broadest terms, the isotopic composition of
soil organic carbon (SOC) reflects that of the local
plant cover (Deines 1980). However, the δ13C value
of SOC differs by –6·1‰ to + 4·4‰ compared to
that of C derived from local vegetation (Rightmire &
Hanshaw 1973; Stout, Goh & Rafter 1981; Nadelhoffer & Fry 1988; Mellilo et al. 1989; Nakamura, Takai
& Wada 1990; von Fischer & Tieszen 1995). The difference between δ13C of SOC and that of soil CO2 was
found to vary from –3·2‰ to +2·1‰ (Readon, Allison
& Fritz 1979; Dörr & Münnich 1980; Parada, Long &
Davis 1983; Mellilo et al. 1989; Nakamura, Takai &
Wada 1990; Hesterberg & Siegenthaler 1991; von
Fischer & Tieszen 1995; Dudziak & Halas 1996a,b).
This wide range of isotopic shifts is difficult to
reconcile with the commonly held view that little
fractionation accompanies heterotrophic metabolism
by soil micro-organisms, i.e. the isotope composition
of the SOC should equal that from plant input
(Fritz et al. 1978; Cerling 1984; Quade, Cerling &
Bowman 1989). The variability in the composition
of soil microbial biomass and the fact that microorganisms use various chemical fractions at different
rates suggest that the difference between the δ13C of
plant material, SOC and the δ13C of soil microbial
biomass can potentially be larger than the value of
1–2‰ established for many heterotrophs (DeNiro &
Epstein 1978; Tieszen & Boutton 1988; Hullar et al.
1996).
One source of the observed difference between δ13C
of SOC, CO2 and plant input could be isotope effects
which occur during microbial degradation of plant
108
FEC402.fm Page 109 Wednesday, March 1, 2000 5:54 PM
109
Carbon and 13C in
grassland soils
material (Deines 1980; Fry & Sherr 1988; Balesdent,
Girardin & Mariotti 1993; Ågren, Bosatta & Balesdent
1996). This can be induced by the selective use of
chemical compounds having δ13C values deviating
from that of plant biomass and by kinetic discrimination during microbial metabolism. The δ13C
value of both heterotrophic and autotrophic biomass
is the mass-averaged δ 13C value of diverse biomolecules. Relative to biomass C, secondary metabolites
(aromatics, proteins, isoprenoids) are usually 13Cdepleted, while primary products are 13C-enriched
(Deines 1980; Schmidt & Gleixner 1998). During
metabolism, catabolic reactions prefer the molecules
which have less δ13C, while those with more δ13C are
involved in biomass production (Blair et al. 1985;
Schmidt & Gleixner 1998). δ13C of consumed material would be equal to δ13C of microbial biomass and
respired CO2, if isotope effect of microbial degradation is induced only by selective use. If discrimination during metabolism is important, then consumed
material would have less δ13C related to microbial
biomass δ13C, and more, as related to the δ13C of
respired CO2.
The importance of the isotopic effect of microbial
degradation was determined in 21 grassland soils, by
analysing for the δ13C content of SOC, soil microbial
biomass (Cmic), and CO2 released by aerobic microbial respiration.
Materials and methods

Soil was sampled from grasslands along a temperature gradient, from a mean annual temperature
of 25 °C in northern Australia to 7 °C in southern
Australia (Fig. 1). Grasslands with mean annual
temperatures above 21 °C are tropical grasslands
with a dominance of C4 plants, while decreasing
temperatures result in an increasing dominance of
C3 grasses in more temperate regions. Soil samples
(Table 1) were collected from the top 2 cm of soil at each
sample site three to five locations within a 10–20 m radius
circle and stored field moist at 4 °C prior to analysis.
The soil was analysed for SOC and the δ13C value
of SOC (Bird & Pousai 1997). Cmic and microbial
respiration (CO2), and the δ13C value of each were
analysed using the same samples. Before Cmic and CO2
were measured, the soil was sieved (2·5 mm) and
moisture adjusted to 55–65% WHC (water holding
capacity, ISO 11274 1994) when necessary. Two soils,
Ausg 19 and Ausg 46, were kept at constant moisture
and temperature and used for a long-term experiment.
Measurements (Cmic, CO2) were performed after 3,
10 and 40 days of incubation.
 
Two replicated samples (50 g each) were incubated
in closed vials (600 ml) at 20 °C for 10 days. CO2
production was determined in two periods; from 1
to 3 days and 7–10 days. CO 2 was trapped in
bicarbonate-free 1 N NaOH then released by acid
addition and purified cryogenically and the amount
of purified CO 2 was determined manometrically.
The vessels containing the NaOH solution were
handled in a N2 atmosphere. Deviations between
the replicates did not exceed a coefficient of variation of 8%. The isotopic composition of the CO2
was corrected for the isotopic composition of the
ambient air, which was present in the incubation
vials at the beginning of measurement, using a
simple two-component mixture model (Hesterberg
& Siegenthaler 1991).
The δ13C value measured by the absorption
method might be affected by isotopic fractionation
if the CO2 is not completely absorbed into the
hydroxide solution. We determined the minimum
incubation time necessary to avoid the kinetic discrimination effect using an addition of CO2 of known
volume and δ13C. 94%, 97% and 100% of added
CO 2 was trapped into NaOH solution in 15, 30
and 60 min after CO2 addition, respectively. No
fractionation was found after 60 min. The incubation
period in the present experiments was at least 72 h.
Therefore, the kinetic effect of absorption was
negligible.
  ⁽   ⁾
© 2000 British
Ecological
Society,
Fig.
1. Location
of Australian grassland soil samples used in this study. Soils are
marked
Ausg
1 to, Ausg 37, from sites in Northern Australia to sites in Southern
Functional
Ecology
Australia.
14, 108 – 114
Cmic was measured after 10 days of incubation
using the chloroform fumigation extraction
method (Vance, Brookes & Jenkinson 1987; Ryan &
Aravena 1994). Soil from each incubation vial was
divided into two portions. One part was exposed
to ethanol-free CHCl3 for 24 h, after which the
FEC402.fm Page 110 Wednesday, March 1, 2000 5:54 PM
110
H. Šantrůčková
et al.
Table 1. Physico-chemical and biological properties of the soils analysed for this study. Respiration rate after 3 (CO 2I), and
10 days (CO2II) of incubation is expressed on an SOC basis (µg CO2.g Corg–1.h–1). Sites Ausg 1–Ausg 21 represent tropical
biomes with C4 plant cover and sites Ausg 23–Ausg 37 temperate biomes with a predominance of C 3 plants
Site
Rainfall Temp.
mm
°C
pHH
Ausg 1
Ausg 4a
Ausg 6
Ausg 8
Ausg 14
Ausg 18
Ausg 19
Ausg 21
Ausg 23
Ausg 25
Ausg 48
Ausg 50
Ausg 52
Ausg 46
Ausg 27
Ausg 29
Ausg 32
Ausg 33
Ausg 35
Ausg 36
Ausg 37
220
220
220
260
220
290
290
290
210
270
240
240
240
240
500
500
640
640
640
640
640
7·5
7·2
7·1
7·3
6·6
6·2
7·7
7·0
7·7
5·3
5·7
7·9
5·7
6·9
6·1
6·1
5·7
4·7
4·1
4·7
7·6
25
25
25
25
24
21
21
21
20
18
16
16
16
15
11
11
8
7
7
7
7
2
O
Respir. rate
Cmic
µg C g–1 CO2I CO2II
C/N
SOC
%
15·1
12·5
20·2
12·6
13·6
12·5
10·5
12·8
9·2
13·4
14·8
12·7
12·3
12·6
12·0
10·2
19·5
21·1
13·5
14·8
17·0
0·34 156
1·22 390
0·35 149
0·29 163
0·33 183
1·41 758
0·72 498
0·50 349
0·90 512
1·20 290
4·08 427
1·63 485
2·46 580
4·56 676
2·85 615
3·17 317
4·81 1107
11·49 568
12·19 849
12·87 1554
2·81 910
fumigant was removed and the soil was extracted
with 0·5  K2SO4 (1/4 w/v ratio, 30 min, end-overend shaker). The second aliquot of the soil, a nonfumigated control, was extracted under the same
conditions but without the fumigation step. One
to two grams of the freeze-dried sulphate extract
was combusted at 900 °C with CuO and silver wire
in evacuated sealed quartz tubes (Boutton et al.
1983). The CO2 released by combustion was purified
cryogenically. Deviations in the amount of carbon
between duplicates did not exceed a coefficient of
variation of 6%.
  
© 2000 British
Ecological Society,
Functional Ecology,
14, 108 – 114
Isotopic composition of CO2 and Cmic was measured
using a Finnigan MAT-251 mass spectrometer. All
measurements were performed in duplicate and the
results are reported as the difference in parts per
thousand (per mil; ‰) from the defined international
V-PDB standard. Precision of the 13C analyses of
standards was ± 0·1‰ and the standard deviation
of the replicate samples did not exceed 0·5‰. δ13C
of C mic ( δ 13C mic) was estimated as the δ 13C of the
C extracted from fumigated soil (δ13Cf) in excess of
that extracted from the non-fumigated control sample
(δ13Cnf):
δ13Cmic = (δ13Cf × Cf – δ13Cnf × Cnf)/(Cf – Cnf).
eqn 1
Estimation of the δ13C value of Cin (organic C consumed
238
104
203
279
291
123
143
206
134
133
106
179
81
64
102
113
64
33
24
8
153
100
38
66
76
103
67
63
112
61
96
55
100
30
29
61
92
55
18
14
7
67
∆
δ13C
of SOC ‰ SOC/Cmic Cmic/CO2 CO2I/CO2II
–14·6
–16·5
–15·3
–15·3
–15·2
–16·4
–15·5
–16
– 20·6
– 22·1
– 25
– 26·8
– 27·5
– 26·6
– 24·8
– 24·8
– 27·1
– 26·8
– 26·1
– 26·1
– 26·7
– 3·1
–1·9
– 2·7
– 3·7
–1·4
–1·3
– 0·8
1·4
– 2·4
1·3
–1·8
– 2·6
–1·9
– 2·1
– 0·9
– 3·2
– 3·3
– 3·3
– 3·3
– 3·0
–1·7
3·27
5·72
3·25
4·06
3·29
1·83
0·38
0·71
0·92
2·98
2·36
2·57
1·33
1·03
1·33
3·18
2·77
2·26
2·15
2·77
0·1
–0·53
–1·94
0·71
0·20
1·70
–0·81
–0·51
1·63
–0·31
–1·03
0·10
–0·10
–2·76
0·31
0·10
–0·21
–0·10
–0·31
–1·13
–0·62
–0·10
by Cmic) was based on the supposition that the δ13C
value of Cmic is the result of a mass balance between
inputs (min ) and outputs (mout ) to the microbial cell
(Hayes 1993). For a microbial cell containing Cmic
moles of C, it can be written that:
dCmic/dt = min – mout
eqn 2
and
dδ13Cmic /dt = (min δ13Cin – mout δ13 CCO2 )/
(min – mout).
eqn 3
McGill et al. (1981) showed that c. 40% of Cin is
converted to Cmic, meaning that c. 60% is released
as CO2. Thus, the amount of δ13C in Cin, used in
aerobic microbial metabolism in soil, was estimated
from the δ13C values of Cmic and CO2 as:
δ13Cin = 0·4 δ13Cmic + 0·6 δ13 CCO2 .
eqn 4
Values of the isotopic composition of δ13Cin and
δ13 CCO2 depend on the isotopic effects accompanying
biosynthesis and catabolism, respectively. δ13C
does not change dramatically if the conversion
efficiency of substrate C is higher or lower than the
suggested value of 0·4, staying within a range of only
0·5‰. For example, if the efficiency of microbial
conversion is decreased to a value of 0·3 or increased
to 0·5 then the proportion of metabolized C/respired
C is changed from 0·4/0·6 to 0·3/0·7 and to 0·5/0·5,
respectively.
FEC402.fm Page 111 Wednesday, March 1, 2000 5:54 PM
& Richards 1984). Four such ‘fractionations’ were
used in this study: (1) the difference between the δ13C
value of C in and the δ 13C value of C mic; ∆Cin/Cmic ;
(2) the difference between the δ13C value of Cin and
the δ13C value of the CO2 respired by Cmic; ∆Cin/CO2 ; (3)
the difference between the δ13C value of SOC and the
δ13C value of Cin; ∆SOC/Cin; (4) the difference between
the δ13C value of CO2 respired after 3 days (CO2I)
and 10 days (CO2II) of incubation; ∆CO2(I)/CO2(II)
111
Carbon and 13C in
grassland soils
Results
Fig. 2. Relationship between SOC, Cmic and mean annual temperature.
The results obtained from the 21 samples analysed
for this study are provided in Table 1. SOC and Cmic
in the soil decreased exponentially with increasing
mean annual temperature (Fig. 2). However, Cmic
decreased more slowly than that of SOC, suggesting
a higher proportion of Cmic in the SOC in tropical
compared to temperate grasslands (Fig. 3).
The δ13C of Cmic reflected that of the corresponding SOC. On average, Cmic was 13C-enriched by –2‰
(Fig. 4). The difference between Cmic and SOC, ∆SOC/C ,
mic
ranged from –3·7‰ to +1·4‰ (Table 1) with no
discernible relationship to SOC, Cmic, SOC-to-Cmic
ratio or biome type (i.e. tropical C4 or temperate C3
grasslands).
CO2 respired by Cmic after 10 days (CO2II) was
13
C-depleted when compared to the corresponding
δ13C-value of Cmic (Fig. 4). The mean value of the
fractionation factor, ∆Cmic/CO2 , was +2·2‰ but ranged
between +0·1‰ and +5·7‰.
Cmic was 13C-enriched relative to Cin, with ∆Cin/Cmic
ranging from –0·1‰ to –3·4‰. Respired CO2 was
depleted, with ∆Cin/CO2 ranging from + 0·04‰ to
+ 2·3‰. δ13C of Cin differed substantially from δ13C
of SOC (Fig. 5a); the values of ∆SOC/C varied from
in
+ 3·1‰ to – 2·0‰.
CO2II differed from CO2I (Table 1), with the values
of ∆CO2(I)/CO2(II) ranging from +1·7‰ to –1·9‰. No
relationship of δ13C of CO2 to respiration rate, SOC,
Cmic, or to environmental factors was discernible.
Over a 40 day incubation period, Cmic in the Ausg
19 and Ausg 46 soils became 13C-depleted, CO2
become 13C-enriched, while Cin did not change. Cmic
and respiration rate decreased over the same period
(Table 2).
Discussion
Fig. 3. Relationship between the ratio of Cmic-to-SOC and mean annual
temperature.
© 2000 British
Ecological Society,
Functional Ecology,
14, 108 – 114
  
 
The difference between two isotopic compositions was
estimated using the fractionation factor, ∆ (Farquhar
The proportion of microbial biomass is larger in
tropical soils than in temperate soils, based on the
observation that the total SOC pool decreased in size
with increasing mean annual temperature at a faster
rate than Cmic. Thus, the turnover rate of organic
material may be quicker in tropical soils. Also SOC
levels in tropical grassland soils will respond more
quickly to changes in carbon input rates than temperate grassland soils. These results are consistent
with those of other studies. Wedin et al. (1995) found
FEC402.fm Page 112 Wednesday, March 1, 2000 5:54 PM
112
H. Šantrůčková
et al.
Fig. 4. Relationship between the δ13C value of Cmic and respired CO2 to the δ13C value
of SOC.
Fig. 5. The magnitude of the difference in isotope composition between (a) C consumed
by micro-organisms (Cin) and SOC ( ∆SOC/C , ‰), (b) respired CO2 and Cin ( ∆C /CO , ‰)
in
2
mic
and (c) Cmic and Cin ( ∆C /C , ‰). Soils are ordered from the highest to the lowest
in mic
mean annual temperature (see text for details).
© 2000 British
Ecological Society,
Functional Ecology,
14, 108 – 114
more rapid turnover of SOC under tropical C4
grasses than under C3 grasses. The mean residence
time of the labile SOC in temperate soils is considered to be in the range of 15–75 years, while it is
only 4–45 years in tropical soils (Jenkinson & Rayner
1977; Bird, Chivas & Head 1996; Hsieh 1996).
The importance of the isotopic effect of microbial degradation of SOC cannot be assessed directly
from the fractionation factor, ∆SOC/C , because only
mic
a small part of the SOC can be used by microorganisms as Cin. Therefore, Cin was estimated, as
were the isotopic shifts resulting from isotopic discrimination during microbial metabolism by using the
fractionation factors ∆Cin/Cmic and ∆Cin/CO2 (Fig. 5).
Cmic was 13C-enriched related to Cin, indicating isotope
discrimination during biosynthesis of new biomass.
The preferential use of 13C for biosynthesis was
approximately balanced by the depletion of CO2,
confirming that catabolic reactions prefer ‘light’ isotopes
(Blair et al. 1985; Schmidt & Gleixner 1998). Cin was
enriched related to SOC in most cases, indicating that
13
C-enriched compounds are preferentially used by
Cmic. Such a selective use induces a more rapid loss of
13
C than 12C during decomposition of plant detritus
(Benner et al. 1987; Ågren, Bosatta & Balesdent 1996).
In those cases when Cin was 13C-depleted relative to
SOC, three of the four soils (AUSG 14, 21 and 25)
were from mixed C3/C4 grasslands; under such circumstances C3 carbon may be preferentially used
over C4 carbon. In addition, in these samples, the
magnitude of ∆Cin/Cmic and ∆Cin/CO2 decreased slightly
with decreasing temperature, possibly owing to the
presence of both C3 and C4 derived SOC. However,
the relationship is unclear at intermediate temperatures.
Many studies have demonstrated that the δ13C
value of SOC increases with both depth in the
soil profile and decreasing particle size (e.g. Bird &
Pousai 1997). The results from this study suggest
that at least part of this increase may be owing to the
preservation/stabilization of a proportion of microbially processed carbon, often in association with the
fine mineral fraction. This carbon has a δ13C value
which is higher than the carbon input to the soil from
local vegetation, owing to the selective utilization of
δ13C-rich organic compounds and isotopic fractionation accompanying heterotrophic metabolism.
The δ13C value of respired CO2 differed after 3 and
10 days of incubation ( ∆CO2I/CO2II ; Table 1). In addition, the δ13C values of CO2 and Cmic changed during
long-term incubation of soils (Table 2). In the early
stage of incubation, when micro-organisms were
growing and microbial activity was higher, Cmic was
more 13C-enriched, suggesting the formation of 13Crich proteinaceous material. However, Cmic and respiration rates decreased during prolonged incubation.
As a result, Cmic became 13C-depleted relative to the
earlier period of incubation. The shift in the δ13C of
Cmic was balanced by an opposite shift in δ13C of
respired CO2. Therefore, heterotrophic shifts in the
δ13C values of Cmic and respired CO2 can be influenced also by the growth stage of the microbial population. Micro-organisms synthesize cell compounds
with different δ13C values at various growth stages.
FEC402.fm Page 113 Wednesday, March 1, 2000 5:54 PM
113
Carbon and 13C in
grassland soils
Table 2. The amounts (mean ± standard deviation, n = 3) and δ13C values of microbial biomass (Cmic) and respired CO2 after
3, 10 and 40 days of incubation for a tropical (Ausg 19) and a temperate (Ausg 46) soil kept at constant moisture content and
temperature. δ13C of actually consumed C (Cin) was estimated using equation 3 (see text for details): ND, not defined
Days of incubation
Soil(δ13C of SOC)
Ausg 19 (–16·4‰)
Ausg 46 (–26·6‰)
Cmic (µg C g–1)
δ13C – Cmic (‰)
CO2(mg CO2 – C g Cmic–1 h–1)
δ13C – CO2 (‰)
δ13C – Cin (‰)
Cmic (µg C g–1)
δ13C – Cmic (‰)
CO2(mg CO2 – C g Cmic–1 h–1)
δ13C – CO2 (‰)
δ13C – Cin (‰)
Growing cells synthesize mainly proteinaceous
compounds rich in 13C (Deines 1980) while growthlimited cells produce mainly storage material which
is depleted in 13C. Coffin et al. (1989) observed that
the δ13C value of bacterial cells grown in sea water
decreased with corresponding increase in the C/N
ratio of the cells and with a prolonged incubation.
This implies that the δ13C value of the storage material which contributes to the increase in the C/N ratio
of a bacterial cell is 13C-depleted.
The results presented in this study demonstrate
that: (1) there is a faster turnover of SOC in tropical
grassland soils, with a higher proportion of microbial biomass in the SOC of tropical grassland soils
relative to temperate grassland soils; (2) on average, the isotope shift of Cmic with respect to SOC is
balanced by an inverse isotope shift of the δ13C value
of respired CO2 resulting in the δ13C value of respired
CO2 being approximately similar to the δ13C of SOC;
(3) an isotope effect of microbial degradation of organic
material can induce a shift in isotopic composition
of SOC. It can be induced by both the selective use
of organic compounds and isotope discrimination
during microbial metabolism. The degree of isotopic
discrimination during metabolism is dependent on
the growth stage of the microbial population.
Acknowledgements
The authors acknowledge the Australian Research
Council for a Queen Elizabeth II Fellowship to
M.I.B.; Grant Agency of Academy of Sciences of the
Czech Republic (A6066901); Joan Cowley and Joe
Cali for assistance with sample preparation and mass
spectrometry measurements and Dr Keith Edwards
for English revision.
© 2000 British
Ecological Society,
Functional Ecology,
14, 108 – 114
References
Ågren, G.J., Bosatta, E. & Balesdent, J. (1996) Isotope
discrimination during decomposition of organic carbon:
3
10
40
ND
ND
1·03 ± 0·04
–15·5
ND
ND
ND
2·92 ± 0·10
– 26·6
ND
498 ± 17
–15·4
0·45 ± 0·03
–15·1
–15·2
676 ± 24
–24·6
1·31 ± 0·01
– 26·9
– 26·0
450 ± 26
–18·7
0·36 ± 0·03
–13·2
–15·4
580 ± 31
–27·5
0·52 ± 0·03
–24·5
–25·7
a theoretical analysis. Soil Science Society of America
Journal 60, 1121–1126.
Balesdent, J., Girardin, C. & Mariotti, A. (1993) Site-related
δ 13C of tree leaves and SOC in a temperate forest.
Ecology 74, 1713 –1721.
Benner, R., Fogel, M.L., Sprague, E.K. & Hodson, R.E.
(1987) Depletion of 13C in lignin and its implications for
stable isotope studies. Nature 329, 708–710.
Bird, M.I. & Pousai, P. (1997) δ13C variations in the surface
SOC pool. Global Biogeochemical Cycles 11, 313–322.
Bird, M.I., Chivas, A.R. & Head, J. (1996) A latitudinal
gradient in carbon turnover times in forest soils. Nature
381, 143 –145.
Blair, N., Leu, A., Munǒz, E., Olsen, J., Kwong, E. &
des Marais, D. (1985) Carbon isotopic fractionation
in heterotrophic microbial metabolism. Applied and
Environmental Microbiology 50, 996–1001.
Boutton, T.W., Wong, W.W., Hachey, D.L., Lee, L.S.,
Cabrera, M.P. & Klein, P.G. (1983) Comparison of quartz
and Pyrex tubes for combustion of organic samples for stable
isotope analysis. Analytical Chemistry 55, 1832–1833.
Cerling, T.E. (1984) The stable isotopic composition of
modern soil carbonate and its relationship to climate.
Earth and Planetary Science Letters 71, 229–240.
Coffin, R.B., Fry, B., Peterson, B.J. & Wright, R.T. (1989)
Carbon isotopic compositions of estuarine bacteria.
Limnology and Oceanography 34, 1305–1310.
Deines, P. (1980) The isotopic composition of reduced
organic carbon. Handbook of Environmental Isotope
Geochemistry, vol. 1 (eds P. Fritz & J. Ch. Fontes),
pp. 329 – 406. Elsevier, Amsterdam.
DeNiro, M.J. & Epstein, S. (1978) Influence of diet on the
distribution of carbon isotopes in animals. Geochimica et
Cosmochimica Acta 42, 495–506.
Dörr, H. & Münnich, K.O. (1980) Carbon-14 and carbon13 in soil CO2. Radiocarbon 22, 909–918.
Dudziak, A. & Halas, S. (1996a) Influence of freezing and
thawing on carbon isotope composition in soil CO 2.
Geoderma 69, 209 –216.
Dudziak, A. & Halas, S. (1996b) Diurnal cycle of carbon
isotope ration in soil CO2 in various ecosystem. Plant and
Soil 183, 291–299.
Farquhar, G.D. & Richards, R.A. (1984) Isotopic composition of plant carbon correlates with water use efficiency
of wheat genotypes. Australian Journal of Plant Physiology
11, 539 –552.
von Fischer, J.C. & Tieszen, L.L. (1995) Carbon isotope
characterisation of vegetation and SOC in subtropical
forests in Luquillo, Puerto Rico. Biotropica 27, 138–148.
FEC402.fm Page 114 Wednesday, March 1, 2000 5:54 PM
114
H. Šantrůčková
et al.
© 2000 British
Ecological Society,
Functional Ecology,
14, 108 – 114
Fritz, P., Reardon, E.J., Barker, J., Brown, R.M., Cherry, J.A.,
Killey, R.W.D. & McNaughton, D. (1978) The carbon
isotope geochemistry of a small groundwater system in
northeastern Ontario. Water Resources Research 14,
1059 –1067.
Fry, B. & Sherr, E.B. (1988) δ13C measurements as indicators of carbon flow in marine and freshwater ecosystems.
Stable Isotopes in Ecological Research (eds P. W. Rundel,
J. R. Ehleringer & K. A. Nagy), pp. 196 –229. SpringerVerlag, New York.
Hayes, J.M. (1993) Factors controlling 13C contents of sedimentary organic compounds: principles and evidence.
Marine Geology 113, 111–125.
Hesterberg, R. & Siegenthaler, U. (1991) Production and
stable isotopic composition of CO2 in a soil near Bern,
Switzerland. Tellus 43B, 197 –205.
Hsieh, Y.P. (1996) SOC pools of two tropical soils interferred by carbon signatures. Soil Science Society of
America Journal 60, 1117–1121.
Hullar, M.A.J., Fry, B., Peterson, B.J. & Wright, R.T. (1996)
Microbial utilization of etuarine dissolved organic carbon:
a stable isotope tracer approach tested by mass balance.
Applied and Environmental Microbiology 62, 2489 –2493.
ISO 11274 (1994) Soil quality – determination of water –
retention characteristics – laboratory methods. International
Organization for Standardization, Geneva, Switzerland.
Jenkinson, D.S. & Rayner, J. (1977) The turnover of SOC
in some of the Rothamsted classical experiments. Soil
Science 123, 298 – 305.
McGill, W.B., Hunt, H.W., Woodmansee, R.G. & Reuss, J.O.
(1981) Phoenix, a model of the dynamics of carbon and
nitrogen in grassland soils. Ecological Bulletins 33, 49 –115.
Mellilo, J.M., Aber, J.D., Linkins, A.E., Ricca, A., Fry, B.
& Nadelhoffer, K.J. (1989) Carbon and nitrogen dynamics
along the decay continuum: plant litter to soil organic
carbon. Plant and Soil 115, 189–198.
Nadelhoffer, K.J. & Fry, B. (1988) Controls on natural
nitrogen-15 and carbon-13 abundances in forest SOC.
Soil Science Society of America Journal 52, 1633 –1640.
Nakamura, K., Takai, Y. & Wada, E. (1990) Carbon isotopes
of soil gases and related organic carbon in an agroecosystem
with special reference to paddy field. Geochemistry of
Gaseous Elements and Compounds (eds E. M. Durrance,
E. M. Galimov, M. E. Hinkle, G. M. Reimer, R. Sugisaki
& S. S. Augustithis), pp. 455–484. Theoprastus Publications, Athens.
Parada, C.B., Long, A. & Davis, S.N. (1983) Stable-isotopic
composition of soil carbon dioxide in the Tuscon Bazin,
Arizona, U.S.A. Isotope Geoscience 1, 219–236.
Quade, J., Cerling, T.E. & Bowman, J.R. (1989) Systematic
variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects
in the southern Great Basin, United States. Geological
Society of America Bulletin 101, 464–475.
Readon, E.J., Allison, G.B. & Fritz, P. (1979) Seasonal chemical
and isotopic variations of soil CO2 at Trout Creeg, Ontario.
Journal of Hydrology 43, 355–371.
Rightmire, C.T. & Hanshaw, B.B. (1973) Relationship between
the carbon isotope composition of soil CO2 and dissolved
carbonate species in groundwater. Water Resource Research
9, 958 – 967.
Ryan, M.C. & Aravena, R. (1994) Combining 13C natural
abundance and fumigation-extraction methods to investigate soil microbial biomass turnover. Soil Biology and
Biochemistry 26, 1583 –1585.
Schmidt, H.-L. & Gleixner, G. (1998) Carbon isotope effects
on key reactions in plant metabolism and 13C-patterns
in natural compounds. Stable Isotopes and the Integration
of Biological, Ecological and Geochemical Processes
(ed. H. Griffiths), pp. 13–26. BIOS Scientific Publishers,
Oxford.
Stout, J.D., Goh, K.M. & Rafter, T.A. (1981) Chemistry and
turnover of naturally occuring resistant organic compounds in
soil. Soil Biochemistry, vol. 5 (eds E. A. Paul & J. N. Ladd),
pp. 2 –73. Marcel Dekker, New York.
Tieszen, L.L. & Boutton, T.W. (1988) Stable isotopes in terrestrial ecosystem research. Stable Isotopes in Ecological
Research (eds P. W. Rundel, J. R. Ehleringer & K. A. Nagy),
pp. 167 –195. Springer-Verlag, New York.
Vance, E.D., Brookes, P.C. & Jenkinson, D.S. (1987) An
extraction method for measuring soil microbial biomass
C. Soil Biology and Biochemistry 19, 703–707.
Wedin, D.A., Tieszen, L.L., Bradley, D. & Pastor, J. (1995)
Carbon isotope dynamic during grass decomposition and
SOC formation. Ecology 76, 1383–1392.
Received 3 December 1998; rrevised 12 August 1999;
accepted 18 August 1999