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Soil Biology & Biochemistry 32 (2000) 527±543
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Decomposition of 13C-labelled plant material in a European 65±
408 latitudinal transect of coniferous forest soils: simulation of
climate change by translocation of soils
Pierre Bottner a,*, Marie-Madeleine CouÃteaux a, Jonathan M. Anderson b, BjoÈrn Berg c,
Georges BilleÁs a, Tom Bolger d, Herve Casabianca e, Joan Romanya f, Pere Rovira f
a
CEFE-CNRS, 1919 Route de Mende, 34293 Montpellier Cedex 5, France
Department of Biological Sciences, Hatherly Laboratories, University of Exeter, Prince of Wales Road, Exeter EX4 4PS, UK
c
Department of Forest Soils, Swedish University of Agricultural Sciences, P.O. Box 7001, S-750 07 Uppsala, Sweden
d
Department of Zoology, University of Dublin, Bel®eld, Dublin 4, Ireland
e
Service Central d'Analyse, CNRS, BP 22, 69390 Vernaison, France
f
Dept Biologia Vegetal, Universitat de Barcelona, 645 Diagonal, 08028 Barcelona, Spain

b

Accepted 27 September 1999

Abstract
Standard 13C-labelled plant material was exposed over 2±3 yr at 8 sites in a north±south climatic gradient of coniferous forest
soils, developed on acid and calcareous parent materials in Western Europe. In addition to soils exposed in their sites of origin,
replicate units containing labelled material were translocated in a cascade sequence southwards along the transect, to simulate
the e€ects of climate warming on decomposition processes. The current Atlantic climate represented the most favourable soil
temperature and moisture conditions for decomposition. Northward this climatic zone, where the soil processes are essentially
temperature-limited, the prediction for a temperature increase of 38C estimated a probable increase of C mineralisation by 20±
25% for the boreal zone and 10% for the cool temperate zone. Southward the cool Atlantic climate zone, (the Mediterranean
climate), where the processes are seasonally moisture-limited, the predicted increase of temperature by 1±28C little a€ected the
soil organic matter dynamics, because of the higher water de®cit. A signi®cant decrease of C mineralisation rates was observed
only in the super®cial layers recognised in Mediterranean forest soils as `xeromoder' and subject to frequent dry conditions. In
the deeper Mediterranean soil organic horizons (the mull humus types), representing the major C storage in this zone, C
mineralisation was not a€ected by a simulated 28C temperature increase. The temperature e€ect is probably counteracted by a
higher water de®cit. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Decomposition; Carbon; Coniferous forests; 13C-labelling; Climate change; North±south transect; Translocation; Organic matter; Carbon mineralisation; Forest soils; Europe; Tracer techniques

1. Introduction

One of the key issues in climate change research
is the future dynamics of organic carbon in soils
which contains about two-thirds of the total organic
C in terrestrial systems. Even small changes of the

* Corresponding author. Fax: +33-4-6741-2138.
E-mail address: bottner@cefe.cnrs-mop.fr (P. Bottner).

mineralisation rates of these large soil pools could
therefore have signi®cant e€ects on concentrations
of atmospheric CO2. As yet there are few indications
as to whether soils will be net sources of CO2, since
climate warming increases mineralisation rates, or net
sinks for C as a consequence of the CO2 e€ect on
plant litter production, quality and decomposition
rates (CouÃteaux et al., 1991; Cotrufo et al., 1994). A
number of di€erent approaches have been used to ob-

0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 9 9 ) 0 0 1 8 2 - 0

528

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

serve these trends which involve ®eld measurements,
manipulative experiments and simulation models.
The net changes in the balances between C input
to soils and mineralisation rates are generally too
small to detect by direct measurements, because of
the variability of the ¯uxes and pools. Using indirect evidence, a large current terrestrial CO2 sink in
the northern hemisphere, referred as `missing sink' was
indicated (i) by atmospheric chemistry measurements:
CO2 pressure gradients (Tans et al., 1990), CO2
13
C/12C ratio (Ciais et al., 1995) and O2 concentration
(Keeling et al., 1996) and (ii) by analysis of climate
variability during the last decades (Dai and Fung,
1993).
The e€ect of climate controls over soil C

dynamics at geographical scales have been investigated using a number of di€erent approaches. Soil
respiration data have been extensively employed in
empirically-based statistical models, to predict
annual and global CO2 emission from terrestrial soils
(Raich and Schlesinger, 1992) and to de®ne the spatial
and temporal climate controls of soil respiration
(Raich and Potter, 1995). Since a possible imbalance in
the ecosystem C cycle arises from the di€ering responses of production and decomposition to temperature change, the mechanistic models are generally
based on coupled production and decomposition submodels. A relatively simple model developed by Townsend et al. (1992) describes the temperature e€ect on
net ecosystem production using a linear function and
an exponential function for response by soil respiration. More complex decomposition models partition
the organic matter into multiple C and N pools with
speci®c turnover rates (Jenkinson et al., 1991; Schimel
et al., 1994). Production- and decomposition-submodels have been linked by the litter quality and plant
detritus chemistry (C-to-N ratio and lignin content)
and by the nitrogen cycle (the dynamics of N mineralisation controlling N uptake by the plants). The spatial
dimension of the decomposition models necessitated
the integration of the geographical distribution of soil
types and some essential intrinsic soil properties.
In our study 13C- and 15N-labelled standard plant

material was exposed, at eight sites along a north±
south climatic gradient of coniferous forest soils in
Western Europe, which included boreal, Atlantic and
Mediterranean climates. In addition, the soils with
their labelled plant material were translocated from
north to south according to a cascade procedure, in
order to simulate a south to north climate shift. The
objective was to investigate the decomposition processes in the climatic transect, where the current climatic spatial di€erences were used as an analogue for
expected climate change. This publication only presents results for 13C dynamics.

2. Materials and methods
2.1. The sites and humus types
Within each climatic zone, except for boreal, two
sites were identi®ed (on acidic and calcareous parent
materials; Fig. 1 and Table 1). In boreal coniferous
forests the surface organic layers are generally of low
pH irrespective of the base status of the underlying
parent material. The complement of sites detailed in
Table 1 included representatives of the major humus
types developed under coniferous forest stands on

well-drained soils in Western Europe. The series of
humus types developed on acid soils included, from
north to south: `mor' (Oh horizons at Vindeln and
JaÈdraaÊs), acid `mull' (A1 horizons at Haldon, TheÂzan
and Desert) and acid `xeromoder' (Oh at TheÂzan). The
calcareous soils series comprised acid `mull' at Friston,
`calcic mull' at La Clape (where the exchange capacity
was saturated by Ca2+ without the presence of carbonates), `calcareous mull' at Maials (Ca2+ saturated
exchange capacity with presence of carbonates) and
®nally neutral `xeromoder' at la Clape and Maials.
Mor and xeromoder are Oh horizons where the organic layer with a high C content, and high C-to-N
ratio (Fig. 2) is developed on the surface of the mineral soil, resulting from the slow turnover rates of low
quality litters under temperature-limited conditions in
the boreal region (mor) and under moisture limitation
in the Mediterranean region (xeromoder). The mull
soils are mainly developed under Atlantic and Mediterranean conditions where organic matter decomposing
at higher rates is incorporated into the mineral soil, by
faunal activity, forming stabilised organo-mineral complexes. On acid soils, the pH (H2O) values of mull are
5±6, irrespective of the climatic conditions (Fig. 2). In
the calcareous soils sequence, the pH values, the Ca2+

saturation and the carbonate concentrations in the
mull soils increase from north to south, indicating a
decreasing capacity of dissolution and leaching of carbonates from the organic horizon. At TheÂzan, La
Clape and Maials, the Oh horizon (xeromoder) overlies the A1 horizon (mull). This is a common situation
under Mediterranean conditions (Fig. 2).
2.2. 13C and
cylinders

15

N soil labelling and ®eld incubation in

The soil was divided into pedological horizons
(Fig. 2) de®ned by the distribution of organic matter
in the pro®le. The material from each horizon was
sieved (4 mm mesh) and thoroughly homogenised. The
material from the horizons selected for labelling was
air-dried in the laboratory before the labelled plant
material was added to the soil. The moist materials
from the unlabelled horizons were placed in increments

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

in plastic cylinders (inside dia 12 cm, length 30 cm)
and packed down with a heavy metal ram to reconstitute a bulk density close to the ®eld value. Discs of 1
mm mesh polyester netting were placed between the
horizons to facilitate sampling. The depth and mass of
the horizons established for each experimental unit are
given in Fig. 2.
The labelled plant material was produced by growing wheat (`Florence Aurore', an old spring-wheat cultivar with low N requirements) over 4 months, in a

529

labelling chamber with facilities for maintaining temperature, radiation, moisture and CO2 conditions, in a
nutrient solution with low 15N, P and K concentrations, plus micro-nutrients, under a 13CO2-labelled
atmosphere. In order to obtain material with a high Cto-N ratio, only the stems and leaves were used in the
experiment. The harvested plant material was airdried, milled into 2±7 mm long ®brous particles and
homogenised.
The labelled plant material was added separately to

Fig. 1. Location of the research plots on a climate and soils transect in Western Europe extending from latitude 658 to 408. The arrows indicate
the north to south sequential translocation of acidic and calcareous soils to simulate the e€ects of projected patterns of climate change on soil
processes.

530

neutral xeromoder (Oh)
calcareous mull (A1)a

acid xeromoder (Oh) acid
mull (A1)a
neutral xeromoder (Oh) calcic
mull (A1)a
acid mull (A1)

neutral mull (A1)

acid mull (A1)

ferric podzol

humo-ferric
podzol
acid (shale)
dystric
luvisol
calcareous (chalk)
humic
cambisol
acid (sandstone)
chromic
luvisol
calcareous (hard limestone) chromic
cambisol
acid (sandstone)
chromic
luvisol
calcareous (marl colluvium) calcic
regosol

mor (Oh)

mor (Oh)

each replicate sample (Table 2) of soil and mixed for
15 min. The labelled soil was then added to the cylinders on top of the unlabelled material and packed to
the appropriate bulk density. The thickness of the
labelled horizons ranged from 3 cm for the Oh layers
to 4±5 cm for the A1 layers (Fig. 2). To complete the
reconstituted pro®le, the soil surfaces were covered by
litter or moss according the characteristics of the ®eld
site. The units were then moistened with 200 ml deionised water. For each pro®le, 28±36 cylinders were
installed (seven to nine sampling occasions and four
replicates). At TheÂzan, La Clape and Maials, the Oh
and A1 horizons were labelled separately (Fig. 2), so
that the number of cylinders was doubled.
2.3. Soil translocation, cascade experiment

At Thezan, La Clape and Maials, the xeromoder overlies the mull horizon; both layers were investigated.
a

Pinus halepensis 30
dry mediterranean (warm temperate)
038 30' E
418 22'
Maials (Spain)

Pinus pinaster >100
008 00'
408 06'
Desert (Spain)

dry mediterranean (warm temerate)

038 08' E
La Clape (France) 438 09'

moist mediterranean (warm temperate) Pinus halepensis > 100

028 45' E
438 07'
Thezan (France)

moist mediterranean (warm temperate) Pinus pinaster >100

Pinus sylvestris >55
008 12' W atlantic (cool temperate)
508 37'
Friston (UK)

Picea abies 52
038 4' W
508 37'
Haldon (UK)

atlantic (cool temperate)

acid (moraine sand)
acid (moraine sand)
Picea abies 100
Pinus sylvestris 140
boreal
boreal
218 05' E
168 01' E
648 00'
608 49'

Vindeln (Sweden)
JaÈdraaÊs (Sweden)

Forest type Stand age (yr) Parent material
Latitude (North) Longitude Climate type
Sites

Table 1
Geographical, climatic and geological characteristics of the sites. Vegetation-, soil- and humus-types

Soil types
(FAO)

Humus types (organic matter
horizons)

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

In addition to soils exposed at their site of origin,
replicate units were translocated to simulate the predicted e€ects of climatic changes on carbon dynamics.
Within each soil series (acid and calcareous soils) the
soils were transplanted from a northern site (the source
site) to the next southern site (the host site) (Figs. 1
and 3). In order to preserve the physical and chemical
environment of the labelled horizon, in each case the
translocated soils comprised the labelled horizon and
the unlabelled horizons above and below this layer,
from the source site but the deeper (B) horizon was
reconstituted using material from the host site. The
untranslocated `control' soils are referred to below as
the `native soils'. For the whole experiment, 704 cylinders were installed. The cylinders were randomly distributed in the sites. After the ®rst year, the litterfall
was removed from the cylinders and replaced by the
litter fallen during this time in the source site. During
the following years the litterfall in the cylinders was
not controlled.
2.4. Sampling procedures and soils analyses
The cylinders were installed during spring and summer 1993 for the acid soils and during winter 1993 and
spring 1994 for the calcareous soils. Four replicate
units were randomly sampled on seven (Vindeln), eight
(JaÈdraaÊs) and nine (the other sites) occasions over 2 yr
(Haldon and Friston), or over 3 yr (the other sites) up
to March 1997.
After collection from the ®eld, the soil column was
pushed out of the cylinders, and the horizons separated at the polyester mesh disks (Fig. 2). The unlabelled horizons were air-dried. The labelled soil was
either prepared immediately or stored over a maximum
of 7 d at 48C. In either case, the moist soil was
thoroughly mixed and subsampled for analysis of total
C and 13C, microbial biomass C and 13C and organic
matter fractionation.

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

531

Fig. 2. Structural composition of labelled and unlabelled horizons in the soil cylinders, and physical and chemical characteristics of the soils. At
TheÂzan, La Clape and Maials both Oh and A1 horizons were labelled.

532
P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

Fig. 3. Translocation between climate zones of humus types in the cascade series of acidic and calcareous soils.

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

2.5. C, N and mass spectrometry analysis

3. Results
3.1. Isotopic

Since highly labelled plant material was added to
the soils in small amounts, preparation methods
were investigated to determine the sample homogeneity required to reduce variation in results of mass
spectrometry. The following procedures were carried
out on the labelled horizons and on the soil materials above and below this layer.
For the mineral soil samples (A1 horizons), about
60% of the initial mass remained after subsampling
for microbial biomass (and inorganic N). This material was air-dried and homogenised. One-third was
stored for organic matter fractionation and the
remaining material was ground in a blender for 5
min. One-third of this ground material was ground
again using a ball mill (Retsch MM2, 10 ml cups,
10 min) and then a third of this material was
ground again to a ®nal ®ne powder using a liquid
N freeze mill (Spex 6700 freezer/mill, 5 min). For
the labelled Oh horizons (mor and xeromoder) the
blender was replaced by a ultracentrifuge mill
(Retsch ZM1).
Total C, and 13C isotopic ratios were measured at
the Service Central d'Analyses of the CNRS, Solaize
(France), using a CN elemental analyser (CNRS)
coupled with a mass spectrometer (Finnigan delta S or
MAT 252).
One analysis was generally carried out for each
®eld replicate, but 10±25 replicates were initially
analysed (time `t0') according to humus types. This
was necessary for two reasons. Firstly, it was dicult
to obtain homogeneous soil samples because the undecomposed labelled wheat material was initially resistant to grinding, and secondly, it was necessary to
obtain very accurate initial values for isotope ratios,
since the 13C remaining in soils during the ®eld exposure period was calculated in percent of the initial
material.
The natural 13C isotopic ratio, measured in four
replicates at each site before the installation of the
experiment, varied from 1.081 to 1.083%. The 13C
derived from added plant material was calculated,
using the 13C isotopic enrichments: enrichment
ˆ
atom% excess
ˆ
…measured isotopic ratio
ÿ
natural isotopic ratio†  100: In highly labelled experiments this formulation was preferable to d13C (Boutton, 1991). In Table 2, d13C - varied from
+262 to +56 for the initial soil 13C and from +67 to
+5 for the ®nal soil 13C. In the ®gures the bares represent the standard deviation for the four replicates.
The comparison of data was performed using the test
of Student ( p value).

533

13

C

The characteristics of the labelled material were:
C ˆ 40:220:2%; 13 C isotopic ratio ˆ 10:54020:013%;
N ˆ 1:2820:02% …15 N isotopic ratio ˆ 9:73520:018%†
and C-to-N ratio ˆ 31:4: The added N in the labelled
plant material, as % of soil native total N, ranged
between 0.8 and 3.4%. The added C in plant material,
expressed as % of soil native organic C, ranged generally from 1.5 to 3.4%. The initial isotopic ratios
measured at t0 for the experiment ranged from 1.173
to 1.399%. The ®nal isotopic ratios measured on the
last sampling occasion after 2±3 yr ®eld exposure ranged from 1.116 to 1.184% (Table 2). These ratios were
signi®cantly di€erent from 1.081±1.083% determined
for the unlabelled soils sampled before the experiment
(P < 0.01). Thus, because of the low N and high 13Clabelling, the plant material could be added to the soil
as a very small proportion of the total mass, that is
without changing the chemical, physical and biological
properties of the soil native organic matter and the tracer was suciently concentrated to be detected
throughout the experiment.
3.2. Transfers of labelled C
In all cases the 13C isotopic ratios in the layers
located directly above the labelled horizons were close
to the natural ratios. Hence upwards transfers of the
labelled-C (for instance by fungi) were negligible. The
13
C measured in the horizon located directly below the
labelled one was also low, ranging from 2 to 7% of
the initial 13C. The highest 13C leaching occurred in
the Vindeln (boreal) soil of 4±7% of the initial 13C.
The lowest values were observed in the acid Mediterranean soils with generally less than 3% of the initial
label. Data for 13C in these adjacent horizons are not
presented separately.
3.3.

13

C mineralisation rates

Fig. 4(a and b) shows the percentage 13C remaining
in soils (sum of 13C remaining in the initially labelled
horizon plus the 13C recovered in the horizons located
directly under and above the initially labelled layer).
For technical reasons, the installation of the experiment in the donor site for the native soil and in the
host site for the translocated soil was generally not
achieved exactly at the same date. The time scale is
therefore shown as exposure days for both native and
transplanted soils, rather than from the date on installation. Fig. 4(a and b) illustrates the dynamics of 13C
mineralisation assuming that (i) the leaching of
labelled carbon below the layers analysed was negli-

534

1.127
0.0017
1.184
0.0051
1.136
0.0036
1.142
0.0056
1.116
0.0013
1.160
0.0019

1.139
0.0039

1.128
0.0075

1.128
0.0079

1.185
0.0081

1.173
0.030
13
1.082
1.280
0.014
10
1.083
1.230
0.022
19
1.082
1.206
0.013
20
1.082
1.194
0.012
35
1.082
1.275
0.022
22
1.081

1.253
0.009
19
1.082

1.200
0.024
19
1.083

1.191
0.018
32
1.082

1.399
0.03
26
1.082

1.10
1.08
1.10
1.13
2.98
2.23
0.92
1.84
1.96
0.90
3.39
1.77
1.12
1.97
1.48
0.82
1.47
1.87
1.09
1.84
2.26
1.19
1.94
0.86
0.94
1.78
0.81
1.31
2.50
3.39

Labelled plant material
Added plant material g cylinderÿ1
1.31
Added C % native soil C cylinderÿ1
2.17
2.19
Added N % native soil N cylinderÿ1
Initial soil 13C (at time 0)
Measured isotopic ratio (%)
1.218
S.D.
0.024
Replicates (n )
29
Measured natural isotopic ratio …n ˆ 4)
1.081
Final soil 13C (measured at the last sampling occasion)
13
C isotopic ratio
1.128
S.D. …n ˆ 4)
0.0054

Table 2
13
C-labelling characteristics

Vindeln Oh

JaÈdraaÊs Oh

Haldon A1

Friston A1

TheÂzan Oh

TheÂzan A1

La Clape Oh

La Clape A1

Desert A1

Maials Oh

Maials A1

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

gible and (ii) 13C remaining in the pro®le can be budgeted as the di€erence between initial 13C and 13CO2
lost by respiration. The ®rst assumption is probably
valid, since the amount of 13C translocated down the
pro®le was low. The second assumption presupposes
that there were no 13C-bicarbonates and carbonates accumulating in the soil from the 13CO2 released by the
soil respiration. This will not occur in acid and neutral
soil but could occur in soils containing CaCO3. The
La Clape soil contained less than 1% carbonates but
was Ca2+ saturated …pH ˆ 7:3). The 13C measured in
the A12 horizon (directly located below the labelled
horizon; Fig. 2) never exceeded 4%, indicating that
13
C immobilisation was probably negligible. In contrast the Maials soil contained 40±42% carbonates in
all horizons and showed unrealistic high 13C values
(15±20%) in the below horizon. In this case 13CO2
may have been immobilised. The di€erentiation of carbonate-13C from organic-13C is necessary to clarify the
CO2-13C sequestration. The results for this soil are
therefore not presented in this paper.
3.4. Soils from the boreal zone
The relocation of soil from Vindeln to JaÈdraaÊs, i.e.
from a north to a more south Scandinavian climate
(Figs. 1 and 3), was accompanied by (i) an increase in
mean annual air temperatures of 2.58C (averaged over
3 yr), (ii) an increase of 17% of the sum of mean daily
temperatures greater than 08C and (iii) a mean annual
precipitation increase of 23% (Table 3). At both sites,
the water de®cit (PET-AET) was low and similar to
the long-term values, except for the second year at
JaÈdraaÊs.
At both Vindeln and JaÈdraaÊs, the experiment was
installed in June 1993. In the native Vindeln soil, the
total soil C remained relatively constant (Fig. 4a).
When transplanted to JaÈdraaÊs, the total C decreased
progressively by 20% and 13C remaining in the translocated soil was 10% lower than the native soil (P <
0.05). During the ®rst year of incubation, the rapid initial decomposition phase was interrupted during the
6±7 winter months by temperatures falling below 08C.
Consequently both the native and transplanted soils
showed a stepwise pattern of 13C depletion. This e€ect
was not evident during the second (1994±1995) and
third (1995±1996) winters.
The translocation of the JaÈdraaÊs soil from JaÈdraaÊs
(boreal) to Haldon (Atlantic climate) corresponded
over the 3 yr to a mean annual air temperature
increase of 78C. Precipitation increased by a factor of
two over this period. The summer water de®cit was
low at both sites and of the same order of magnitude
( 08 (8C)

year 3

Water de®citb
PET-AET
(mm)

year 3

long
term

Number of months
with PET-AET
> 0 mm

long
term

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

In the acid soil sequence (Figs. 1 and 3), the Haldon
soil (Atlantic climate) was transplanted to TheÂzan (wet
Mediterranean). The soil was thus exposed to an
increase in annual mean air temperature of 5.48C and
a decrease in annual precipitation from 1505 to 731
mm throughout the experiment. The water de®cit also
increased from 47 mm (with PET-AET > 0 over 3
months) at Haldon to 313 mm with 7 months water
de®cit at TheÂzan during spring, summer and autumn
(Table 3). The native soil was installed in September
1993 and the transplanted soil was installed 2 months
later. The total C decreased by 15% of the initial total
C for both soils over 3 yr (Fig. 4a). Translocation of
Haldon soil to TheÂzan resulted in a slower rate of 13C
decrease in the transplanted soil. During the initial and
rapid decomposition phase, the amount of 13C in the
translocated soil was 5±10% higher than in the native
soil (P < 0.05 at samplings 2 and 3). During the slower
decomposition phase, the mineralisation rates became
comparable.
When the calcareous Friston soil (Atlantic climate)
was transplanted to La Clape (wet Mediterranean)
(Figs. 1 and 3) the soil was exposed to an increase in
mean annual air temperature of 3.58C and a decrease
in precipitation from 750 to 572 mm (Table 3). These
values are comparable to long-term records but both
sites experienced a dry summer during the second year
of the experiment. The water de®cit increased from
111 to 281 mm and the dry months increased from 5
to 8.5 at La Clape. The third winter was at La Clape
exceptionally wet with 1199 mm precipitation. Nevertheless, the moisture e€ect of the second and third
year on the 13C mineralisation rates was of little signi®cance since, as shown in Fig. 4a, the pattern of 13C
losses was already stabilised after the ®rst year. The
native Friston soil was installed in March 1994 but the
transplanted soil had already been installed at La
Clape since January 1994. The total organic C content
of the Friston soil decreased by 10±15% for both
native and transplanted soils. The 13C curve of the
translocated soil was generally higher by 5±10% compared to the native soil (0.1 > P > 0.05).
Hence, moisture de®cit limited 13C mineralisation in
the translocated Haldon and Friston soils. In contrast
to the soils maintained under boreal conditions, for

538

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

both native Atlantic climate soils (Haldon and Friston)
and the boreal JaÈdraaÊs soil transplanted to Haldon,
the generally favourable seasonal patterns of moisture
and temperature resulted in steady and regular rates of
13
C mineralisation. The variability was particularly low
for the native Haldon and Friston soils.
3.6. Soils in the Mediterranean zone
In the acid soils series, the xeromoder (Oh) and the
acid mull (A1) of TheÂzan were transplanted from wet
Mediterranean conditions to Desert de les Palmes
(Figs. 1 and 3) which had the driest climatic conditions
in the transect. This involved a (3 yr) mean annual
precipitation decrease from 731 to 387 mm, an increase
in moisture de®cit (PET-AET) from 313 to 453 mm
yrÿ1; the number of dry months (PET-AET > 0)
increased from 7 to 10 and the temperature increased
from 15.5 to 16.58C (Table 3). Units at TheÂzan were
installed in July 1993 and at Desert 3 weeks later. The
curves for residual organic-C and 13C showed greater
variation compared with results from of the Atlantic
sites (Fig. 4b). This was probably the consequence of
the heterogeneous spatial distribution of the Mediterranean vegetation in the sites, creating greater variation in microclimate.
The more arid environment of the transplanted soils
a€ected the pattern of total organic C and 13C losses
from the Oh layer (Fig. 4b). During the ®rst year,
total organic C was reduced by about 20% for the
native soil and 10% for the transplanted soil and 13C
by 55 and 45%, respectively (P < 0.05 at samplings 2
and 3). Over this ®rst year the Desert site was particularly dry with a water de®cit for 10 months compared
to 5 months at TheÂzan. Over the remainder of the experiment, the curves for residual 13C were not signi®cantly di€erent (P > 0.1) for the two soil and
stabilised at relatively high values. In contrast to the
boreal soils where freezing markedly a€ected the 13C
mineralisation curves, the dry summer e€ect of the
Mediterranean soils was probably masked by the high
variability of the data.
Results for the TheÂzan A1 horizon showed high
variability for the same reasons considered for the Oh
material. The curves for total organic C and 13C were
similar for the native and transplanted soil, except on
the ®rst sampling occasion (Fig. 4b).
When the calcareous La Clape soil was transplanted
from a wet Mediterranean climate to dry Mediterranean conditions at Maials (Figs. 1 and 3), the soils
changed from a mean annual precipitation of 781 to
381 mm yrÿ1. The temperature increased from 15.1 to
16.08C. Water de®cit increased from 282 (8 dry
months) to 468 mm yrÿ1 (9 dry months). As with the
TheÂzan soil, the Oh and A1 horizons were investigated
(Fig. 2). Simulating the natural ®eld pro®le, the Oh

horizon was separated from the underlying A1 horizon
by a stone layer (St layer in Fig. 2). The experiment
was installed at La Clape in January 1994 and at
Maials in April.
During the ®rst spring and summer, conditions were
extremely dry with 7±8 dry months and at Maials
there were no decreases in Oh 13C from April (installation) to September. At La Clape in Oh only 10±15%
of the initial 13C was mineralised during this period.
At Maials maximum rates of 13C mineralisation
occurred during the ®rst wet autumn and winter
(1994). During the summer of 1995, mineralisation of
13
C was again reduced. Thus Maials Oh showed a
stepwise pattern of 13C losses controlled by seasonal
alternate dry and wet periods while at La Clape the
drought e€ects were attenuated and only manifested
during the ®rst summer period.
The La Clape labelled A1 mull horizon was located
in the mineral soil under the xeromoder horizon and
the stony layer (Fig. 2). This bu€ered the variability in
moisture conditions at both sites. The dry summer
conditions did not a€ect the 13C mineralisation
(Fig. 4b). This soil, with basic pH and bu€ered moisture conditions, showed high mineralisation rates resulting in 65% 13C loss during the ®rst year. In the native
and transplanted soils, the curves for total organic C
and 13C were similar despite the comparatively low
variability of the data.
3.7. Temperature e€ect on
stabilisation

13

C mineralisation and

Fig. 5 shows the residual 13C in the native and
transplanted soils in relation to the mean annual air
temperatures of the donor and host sites. The slopes
of the lines indicate the temperature e€ect on 13C mineralisation. The increase in soil temperatures produced
by translocation had the largest e€ect (highest negative
slope) on 13C mineralisation between Vindeln and
JaÈdraaÊs, i.e. from north to south boreal conditions.
The 13C mineralisation rates were enhanced over the 3
yr of decomposition as shown by signi®cant (P <
0.001) di€erences in the slopes of V1, V2 and V3. The
translocation from boreal to Atlantic conditions also
produced an increase in 13C mineralisation, but the
slopes are less steep and the temperature e€ect
decreased from the ®rst (J1; P < 0.01) to the last year
(J3; P < 0.05). The temperature increase had no signi®cant e€ects when the Haldon soil was translocated
to TheÂzan and the positive slope for H1 indicates a
tendency …P ˆ 0:13† for 13C mineralisation to decrease
during the ®rst year. For the Friston soil transplanted
to La Clape, the mineralisation of 13C was signi®cantly
reduced during the ®rst (P < 0.01 for F1) and second
years (P < 0.01 for F2). Translocation within the Mediterranean region had no e€ect on 13C mineralisation

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

or resulted after 3 yr in a decreased mineralisation
rates of the La Clape Oh layer transplanted to Maials.
For L(o)3, P < 0.05 and for L(a)3 P ˆ 0:08: The negative slope of La Clape Oh after 1 yr (L(o)1) was transient.

4. Discussion
4.1. Soils in the boreal region
Within the boreal zone, signi®cantly higher 13C
losses (10%) occurred in the Vindeln soil transplanted
to JaÈdraaÊs than in the native soil. The climate e€ect is
con®rmed when both native soils are compared: the residual 13C remaining in the native JaÈdraaÊs soil is by
20% (of the initial 13C) lower than in the native Vin-

539

deln soil. The mean annual air temperature calculated
over the 3 yr of 0.68C in Vindeln and 3.18C in JaÈdraaÊs,
is a realistic predictive ®gure of the northward climate
shift in a 2  CO2 concentration context. Thus, as illustrated in Fig. 6, the southward translocation of the
Vindeln soil to JaÈdraaÊs, decreased the 13C in the transplanted soil in a proportion of 20±25% of 13C of the
native soil. In other words, the expected northward
warmer climate shift would increase the C mineralisation rate in the boreal forest soils by 20±25%.
The Q10 values for the 13C mineralisation rates, derived from data in Fig. 5 (over 3 yr), ranged from 2.6
to 1.6 when the native and transplanted Vindeln soils
were compared and from 1.6 to 1.4 when the native
Vindeln and JaÈdraaÊs soil were compared. Nevertheless
the temperature responses are also a€ected by the soil
moisture regime. The mean water de®cit (PET-AET)

Fig. 5. Residual 13C in soils after 1, 2 and 3 yr of exposure in relation to mean annual temperature (MAT) of donor (native soil) and host (transplanted soil) sites. V=Vindeln, J=JaÈdraaÊs, H=Haldon, F=Friston, L(o)=La Clape Oh horizon, L(a)=La Clape A1 horizon, T(o)=TheÂzan
Oh horizon, T(a)=TheÂzan A1 horizon. Each soil is represented by three lines (year 1, 2 and 3); the left hand end of the lines indicates the
amount of 13C remaining in the native soil; the right hand end of the line indicates the amount of 13C remaining in the translocated soil. For
instance, for JaÈdraaÊs: the left end of lines J1, J2 and J3 indicates 13C remaining in the native JaÈdraaÊs soil (MAT 2.38C) after 1, 2 and 3 yr; the
right end of the line indicates the 13C remaining in the JaÈdraaÊs soil transplanted to Haldon (MAT 9.88C). Vertical bars indicate standard deviation. For clarity, only the lines for years 1 and 3 are shown for the Mediterranean soils (La Clape and TheÂzan); for instance for La Clape Oh:
L(o)1 and L(o)3). Since the 13C mineralisation curves of TheÂzan Oh and A1 were comparable (see text), data for the A1 horizon are not presented. The slopes of the lines indicate the e€ect on 13C mineralisation of the di€erence in annual temperature between the donor (native soil)
and host (transplanted soil) sites.

540

P. Bottner et al. / Soil Biology & Biochemistry 32 (2000) 527±543

was 50 and 19 mm at Vindeln and JaÈdraaÊs, respectively (Table 3). Thus the drier regime in Vindeln could
result in an overestimate of the calculated Q10 values.
However, since at both sites the water de®cit was low
it may not have signi®cantly in¯uenced C mineralisation. Recently, KaÈtterer et al. (1998) calculated from
literature data, that a Q10 of 2 was adequate for a temperature range from 5 to 358. For soils at temperatures
below 58C, they found that the calculation using other
temperature response functions than Q10 are probably
more adequate.
For the native and transplanted soils, the mineralisation pattern was clearly modi®ed by the long period
over which the soils were frozen. This resulted in a
stepwise pattern of 13C losses over the ®rst year with
no signi®cant changes between October 1993 and June
1994 (Fig. 4a). At Vindeln this inactive winter period
was followed by a substantial leaching of 13C from the
labelled horizon into the underlying layer as the soils
thawed. This winter e€ect was not observed in years 2
and 3, probably because the responses of the more
recalcitrant materials were masked by the variability.
In a ®eld experiment of barley straw decomposition in
Sweden (608N) AndreÂn and Paustian (1987) also

observed a similar pattern of mass losses. Raich and
Schlesinger (1992), however, showed in boreal soils
that CO2 evolution continue over the winter period.
Snow cover and the activity in deeper layers will probably contribute to these di€erences in responses.
4.2. Atlantic climate shift toward the boreal forest
The translocation of the JaÈdraaÊs soil to Haldon signi®cantly increased 13C mineralisation rates throughout the experiment and the 13C mineralisation rates in
the native Haldon soil were signi®cantly higher compared to the native JaÈdraaÊs soil (Fig. 5). The JaÈdraaÊs
soil located at Haldon lost 20±25% more 13C than the
same material in the parent site (Fig. 6). However, the
temperature between the two locations increased from
3 to 108C, i.e. greater than the climate warming of 38C
predicted for high latitudes. The Q10 values determined
over the 3 yr for these soils ranged between 1.2 and
1.5. The summer water de®cit was low at both sites
and of the same order of magnitude (