Christina Biasi a,* , Simo Jokinen a , Maija E. Marushchak a , Kai Hämäläinen b,1 , Tatiana Trubnikova a ,
Markku Oinonen b and Pertti J. Martikainen a a University of Eastern Finland, Department of Environmental Science, P.O. Box 1627, 70211 Kuopio,
Finland b Finnish Museum of Natural History, University of Helsinki, Dating Laboratory, P.O. Box 64, 00014
Helsinki, Finland
1 STUK-Radiation and Nuclear Safety Authority, P.O. Box 14, 00881 Helsinki, Finland
* Correspondance: Christina Biasi, Tel.: +358 40 3553810, Fax: +358 17 163750. Email: christina.biasi@uef.fi
1

Climatic characteristics of study site Seida
Mean long-term annual temperature is -5.6 °C and the mean annual precipitation amounts to 501 mm measured between 1977 and 2006 at the closest climate station in Vorkuta, 75 km from the research site (Komi Republican Center for Hydrometeorological and
Environmental Monitoring). Mean annual temperature was 2-3 °C higher than this longterm mean in 2008 and 2007, respectively. The length of the thermic growing season, which is defined as a period when the daily mean air temperature is permanently above +5°C, was
80 days in 2007 and 79 days in 2008 comparable between both years.
Vegetation characteristics of the subsites and plant biomass during the study years
The vegetated areas of peat plateau are dominated by mosses, such as Dicranum sp. and
Hepaticae sp. in dry peat plateau (DPP) and Sphagnum sp. in moist peat plateau (MPP). The dominating vascular plants are Ledum decumbens in DPP and Rubus chamaemorus in MPP.
In both subsites, also Betula nana and Vaccinium sp. are found and in the drier areas, lichens are abundant (for example, Cladina rangifera and C. maxima). The dominant vascular plants of tundra heath (STH) are Betula nana and Carex globularis, and also lichens
(for example, Cladina rangifera and C. maxima) and mosses (for example, Sphagnum sp.,
Polytrichum strictum) are abundant.
We measured plant biomass and plant charactersitics by monitoring height of sedges and length of new growth and number of leaves of dominant vasuclar plants in 2007 and 2008.
This was done periodically over the growing seasons 2007 and 2008 on specifically labelled
2

plants next to collars where respiration measurements were carried out. The results for period DOY203-218, when this study was carried out, are shown in Figure S5 below.
Soil analysis
Soil moisture content was determined on a 10 g subsample by oven drying at 60 °C for 24 h.
Soil pH was measured in a 1:2.5 soil to H
2
O solution (v/v). Carbon and nitrogen (N) contents were determined from a finely ground subsample by elemental analyzer (Thermo Finnigan
Flash EA 1112 Series, San Jose, CA, USA), and soil organic matter (SOM) content was measured as loss on ignition. Dry bulk density of soils was determined by a core method.
A subsample of surface soil from each replicate was pooled and analyzed for radiocarbon content by the Finnish Museum of Natural History, University of Helsinki. Additionally, radiocarbon analyses were performed for the soil profile of peat circles (PC). The sample pretreatment procedure for radiocarbon analyses followed the typical acid-alkali-acid method aiming to separate alkali insoluble fraction of the sample. This procedure removes possible carbonate contaminants and alkali-soluble humic acids. Pretreated samples were mixed with a stoichiometric excess of CuO and packed into glass ampoules, which were pumped into vacuum and torch-sealed. The packed samples were combusted at 520°C overnight. The released CO
2
was collected and purified with liquid-N
2
and ethanol traps at -
196 and -85°C, respectively. After purifying and measuring the sample
 13 C value with IRMS, the CO
2
samples were converted to graphite targets in presence of zinc powder and iron catalyst. AMS measurements on the targets were eventually performed at the Uppsala
Tandem Laboratory.
3

Incubation experiment
Field-moist soil (25 g) was weighed in 500 ml jars and placed in incubators in the laboratory.
Incubation temperature was set to approximate field conditions (± 2°C) (10°C for organic soils of MPP and mineral soils of STH and at 15°C for the other samples). A pre-incubation period of one month, where jars were only loosely covered and water content was adjusted, was carried out to deplete C stemming from residual fine roots including mycorrhiza which contribute to CO
2
flux. Soil respiration rates were then determined by closing the jars and sampling headspace air (20 ml) initially and 4 times over the following six hour incubation time. The CO
2
concentration of headspace air was determined by gas chromatography (GC)
(HP 5890 series II, Hewlett-Packard with a thermal conductivity (TC) detector for CO
2
). Soil respiration was calculated from the linear increase in CO
2
concentration over the incubation period. For comparison of basal soil respiration rates between different soils, all rates were normalized to 15°C using Q
10
values derived from Arrhenius equations (see main text).
For radiocarbon dating of CO
2
, the jars were flushed with CO
2
free air (equivalent five-times chamber volume) to remove background ambient air from the headspace. Jars were thereafter closed until enough CO
2
had accumulated to allow sampling for 14 C. Collection of
14 CO
2
and 13 CO
2
was done following the procedure used for the field and described in the main body of the text. Carbon dioxide collected in the molecular sieves was analyzed for 14 C within one week.
4

14 CO
2
collection
After finishing the SR measurements, CO
2
was collected for 14 CO
2
analysis by the molecular
sieve sampling technique using a protocol modified after Schuur and Trumbore (2006). Prior
to the field sampling, the molecular sieve tubes were filled and regenerated according to the procedure described by Hämäläinen and others (2010). Particularly, the tubes containing 20 g of molecular sieve grains were heated to 500°C and evacuated until the pressure within the tube reached 1×10 -2 mbar. The sieve tubes were then closed by valves at both ends and taken to the field site for collections. In the field, chamber air was scrubbed first through an external soda lime cartridge by pump (flow rate: 4 l min -1 ) to remove background atmospheric CO
2
. To achieve that, the equivalent of five chambervolumes was scrubbed. Then, the pump was switched off and CO
2
(consisting of SMR and
RR) was allowed to accumulate for about 10 minutes while monitoring the concentration with IRGA. The chamber air was then passed through anhydrone to dry the air and the tubes filled with molecular sieves (type 13X, Merck 1.05703.0250) by pumping for 20 minutes or until the saturation of the sieve tube was observed. The CO
2
samples in the sieve tubes were treated in the laboratory as follows. The sieve tube was first evacuated to remove the unwanted volatile material inside. CO
2
was released by keeping the sieve 2h at 500°C. The released CO
2
was then treated correspondingly to soil samples, grafitized and analyzed by
AMS. A full molecular sieve yielded 1.3 ± 0.5 mg of C which is sufficient for radiocarbon dating. The advantage of CO
2
collection with molecular sieves over the traditional NaOH trapping method is that risks of isotope fractionation and contamination are largely reduced
(Bauer and others 1992; Hardie and others 2005).
5

To determine the  13 C of respiration, which was needed for eventual correction of contamination of molecular sieves with air and incomplete scrubbing of atmospheric CO
2
in the chamber system, some Keeling plots were taken at the end of the sampling following
the procedure described in Biasi and others (2008a) and simultaneously an air sample was
taken for  13 C analysis. The  13 CO
2
values were determined by gas chromatography coupled to an isotope ratio mass spectrometer (
GC-IRMS) in the laboratories of Kuopio (Biasi and others 2008b; Biasi and others 2005)
14 C notation
The 14 C content is expressed as fraction modern (F 14
C) (Reimer and others 2004),
representing the proportion of 14 C activity in the sample compared to the 14 C standard activity. As an isotopic fractionation can occur due to the mass difference of the C isotopes, all samples are routinely corrected for mass-dependent fractionation using the
 13 C values.
The typical accuracy of the F 14 C values values was ± 0.004. F 14 C is approximately equal to 1.0 in 1950, before the nuclear weapons test . Higher values reflect the time of nuclear weapon testing (bomb C peak) whereas lower values the pre-bomb times. To obtain the approximate age for the corresponding C fixation by photosynthetic activity, the
radiocarbon data were converted to calendar years via atmospheric calibration data (Levin and others 2008; Levin and Kromer 2004) and IntCal09 (Reimer and others 2009), and by using CaliBomb (Stuiver and Reimer 1986), calib.qub.ac.uk/CALIBomb) and Oxcal 4.1
software.
Often two possible values are provided for post-bomb results (upslope or down-
6

slope of the bomb curve). In some cases, we could rule out one value by assuming the following: mineral soil is older than overlying organic soil; CO
2
respired is younger than bulk soil C; and SR is younger than SMR due to contribution of roots. If some uncertainty remained, both age results were given. In any case, post-bomb age values are considered as approximations, because the atmospheric 14 C concentration after nuclear bomb testing was not uniform around the globe and the calibration data available for this study were from
Central Europe.
Post-processing of measured F 14 C values of CO
2
from molecular sieves
The measured F 14 C values of CO
2
collected in molecular sieves were first corrected for blank values (contamination with atmosphere) using the
 13 C values measured and isotope mixing
models as well as mass balance approaches as described in Schuur and Trumbore (2006).
The contribution of air was on average 11.8% for field samples, and 4.3% for laboratory samples. Samples with greater than 50% air contamination (one replicate of MPP and one replicate of DPP, field samples) were omitted from the study.
7

Figure S1
5
4
3
2
1
Peat Plateau a a a
Tundra Heath b a
0
DPP MPP PC STH
Fig. S1: Basal soil respiration rates from laboratory incubations with root free soil, expressed on a volume basis. DPP, MPP, PC and STH represent dry peat plateau, moist peat plateau, peat circle and shrub tundra heath, respectively. Patterned grey bars indicate mineral soil of
STH, patterned white bars organic soil of STH. Different letter denote significant differences between subsites at p ≤ 0.05 (Kruskal Wallice test).
8

Figure S2
80
70
60
50
40
10
0
30
20
DPP
MPP
PC
STH-Organic horizon
STH-Mineral horizon
0 1000 2000
Age of soil (yrs)
3000 4000
60
50
40
30
80
70
20
10
0
10 20 30 40
Age of soil (yrs)
50 60 70
Fig. S2: Basal soil respiration rates as determined from laboratory incubations (n=3, SE) are correlated with age of soil (SE of analysis). The upper figure includes values of peat circles
(PC). The lower figure excludes them and shows then a significant correlation (p < 0.05). This analysis assumes that the age of MPP is 45 years, but near significant correlation (p < 0.1) is also found if the age of MPP is assumed to be 28 years. It shows that respiration rates of PC are very high for this ancient soil thus breaking the correlation between age and respiration rates.
9

Figure S3
400
300
200
Peat Plateau Tundra Heath
100
*
0
DPP MPP PC STH
Fig. S3: Soil microbial respiration rates as determined with 14 C partitioning approach (white bars) and trenching approach (black bars) in Seida study site, Arctic tundra. Both techniques were employed in two consecutive years in peak season (between 22 July and 6 August).
The star indicates a significant difference between the methods at p < 0.05 (Kruskal-Wallis test).
10

Figure S4
400
-200
-400
200
0
-600
50
DPP
MPP
PC
STH r
2
= 0.75
p < 0.1
100 150 200 250
SMR (g CO
2
m
-2
season
-1
)
300 350
400
-200
-400
200
0
DPP
MPP
PC
STH r
2
= 0.77
p = 0.125
-600
0 100 200
SMR (mg CO
2
m
-2
h
-1
)
300
Fig. S4: Correlations between soil microbial respiration (SMR) and net ecosystem carbon exchange (NEE). Upper graph: soil microbial respiration (SMR) was determined with root trenching. Both fluxes were measured over the growing season 2008 (n=5 for SMR, n=3 for
NEE; SE). Lower Graph: Both fluxes were determined in 2007; SMR rates were calculated by
11

14 C partitioning approach (n=2-3 for SMR, n=3 for NEE; SE). Sunny, clear days prevailed during this period.
12

Figure S5
20
15
2007
2008
New Growth Entire Plant
10
5
0
E m pe tr um
n ig ru m
Le du m
d ec um be ns
V ac cin iu m
u lig in os um
B et ula
n an a
C ar ex
s p.
25
20
15
10
2007
2008
New Growth Entire Plant
5
0
R ub us
c ha m ae m or us
Le du m
d ec um be ns
V ac cin iu m
u lig in os um
B et ula
n an a
C ar ex
s p.
13

Figure S5: Plant characteristics of dominate vascular plant species. Upper graph: height of
Carex sp., and length of new growth of all other vascular plants. Lower graph: leaf number of Carex sp., and leaf number of all other vascular plants of vegetation in 2007 and 2008 growing season (all data are means of 12 measurements for each plant taken between DOY
203-218). There was no significant difference in a single parameter between both years, indicating that plant biomass was comparable in 2007 and 2008.
14

Table S1: Pearson's Correlation Coefficient (R 2 ) and p-values Between Basal Soil Respiration
Rates (  g CO
2
g -1 DW h -1 ) and Relevant Variables as Determined from Root-free Soil during
Laboratory Incubations (univariate analysis)
Correlations that were near significant (p< 0.10) are in italic and correlations that were significant (p< 0.05) are in bold.
Abbreviations are as followed: BD (bulk density), SOM (soil organic matter), WC (water content); age of soil is in years. a assuming that age of soil from MPP is ~28 yrs b assuming that age of soil from MPP is ~45 yrs c assuming that age of CO
2
respired from DPP is ~12 yrs d assuming that age of CO
2 respired from DPP is ~49 yrs
15

Table S2: Pearson's Correlation Coefficient (R 2 ) and p-values Between Soil Microbial
Respiration (SMR
TR; in g CO
2
m -2 season -1 ) and Relevant Variables as Determined with Root
Trenching Approach in 2008, Seida Study Site (univariate analysis)
BD (g cm
-3
) pH
C content (g C m
-2
; 0-10 cm)
N content (g N m
-2
, 0-10cm)
C/N
Moisture (VWC)
Age of soil a
Age of soil b
Age of CO
2
T (°C, 2 cm)
WT (cm)
AL (cm)
NEE (g CO
2
m
-2
season
-1
)
ER (g CO
2
m
-2
season
-1
)
SMR
TR
R
2
0,913
-0,566
0,907
0,91
-0,945
0,953
-0,024
-0,025
-0,016
0,066
-0,013
0,292
0,977
0,384 p-value
0,087
0,434
0,093
0,085
0,055
0,047
0,976
0,975
0,984
0,809
0,961
0,273
0,023
0,142
SMR
TR
(excluding PC)
R
2 p-value
0,268
0,714
0,714
-0,654
-0,747
0,77
0,71
0,713
0,713
0,142
0,904
-0,786
0,861
0,623
0,828
0,494
0,494
0,494
0,463
0,44
0,498
0,495
0,495
0,909
0,282
0,425
0,34
0,572
Correlations that were near significant (p< 0.10) are in italic and correlations that were significant (p< 0.05) are in bold.
Abbreviations are as followed: BD (bulk density), VWC (volumetric water content); WT
(water table), AL (active layer), NEE (net ecosystem carbon exchange), ER (ecosystem respiration). a assuming that age of soil from MPP is ~28 yrs b assuming that age of soil from MPP is ~45 yrs
16

References
Bauer JE, Williams PM, Druffel ERM. 1992. Recoveries of submilligram quantitities of carbon-dioxide from gas streams by molecular sieve for subsequent determination of isotopic (C-13 and C-14) natural abundances. Analytical Chemistry 64: 824-827.
Biasi C, Lind SE, Pekkarinen NM, Huttunen JT, Shurpali NJ, Hyvonen NP, Repo ME, Martikainen PJ.
2008a. Direct experimental evidence for the contribution of lime to CO2 release from managed peat soil. Soil Biology & Biochemistry 40: 2660-2669.
Biasi C, Meyer H, Rusalimova O, Hammerle R, Kaiser C, Baranyi C, Daims H, Lashchinsky N, Barsukov
P, Richter A. 2008b. Initial effects of experimental warming on carbon exchange rates, plant growth and microbial dynamics of a lichen-rich dwarf shrub tundra in Siberia. Plant and Soil 307: 191-205.
Biasi C, Wanek W, Rusalimova O, Kaiser C, Meyer H, Barsukov P, Richter A. 2005. Microtopography and plant-cover controls on nitrogen dynamics in hummock tundra ecosystems in Siberia. Arctic
Antarctic and Alpine Research 37: 435-443.
Hardie SML, Garnett MH, Fallick AE, Rowland AP, Ostle NJ. 2005. Carbon dioxide capture using a zeolite molecular sieve sampling system for isotopic studies (C-13 and C-14) of respiration.
Radiocarbon 2005 47: 441-451.
Hämäläinen K, Fritze H, Jungner H, Karhu K, Oinonen M, Sonninen E, Spetz P, Tuomi M, Vanhala P,
Liski J. 2010. Molecular sieve sampling of CO2 from decomposition of soil organic matter for AMS radiocarbon measurements. Nuclear Instruments & Methods in Physics Research Section B-Beam
Interactions with Materials and Atoms 268: 1067-1069.
Levin I, Hammer S, Kromer B, Meinhardt F. 2008. Radiocarbon observations in atmospheric CO2:
Determining fossil fuel CO2 over Europe using Jungfraujoch observations as background. Science of the Total Environment 391: 211-216.
Levin I, Kromer B. 2004. The tropospheric (CO2)-C-14 level in mid-latitudes of the Northern
Hemisphere (1959-2003). Radiocarbon 46: 1261-1272.
Reimer PJ, Baillie MGL, Bard E, Bayliss A, Beck JW, Blackwell PG, Ramsey CB, Buck CE, Burr GS,
Edwards RL, Friedrich M, Grootes PM, Guilderson TP, Hajdas I, Heaton TJ, Hogg AG, Hughen KA,
Kaiser KF, Kromer B, McCormac FG, Manning SW, Reimer RW, Richards DA, Southon JR, Talamo S,
Turney CSM, van der Plicht J, Weyhenmeye CE. 2009. INTCAL09 AND MARINE09 RADIOCARBON AGE
CALIBRATION CURVES, 0-50,000 YEARS CAL BP. Radiocarbon 51: 1111-1150.
Reimer PJ, Brown TA, Reimer RW. 2004. Discussion: Reporting and calibration of post-bomb C-14 data. Radiocarbon 46: 1299-1304.
Schuur EAG, Trumbore SE. 2006. Partitioning sources of soil respiration in boreal black spruce forest using radiocarbon. Global Change Biology 12: 165-176.
Stuiver M, Reimer PJ. 1986. A computer-program for radiocarbon age calibration. Radiocarbon 28:
1022-1030.
17