Direct experimental evidence for the contribution of lime to CO2 release from managed peat soil

Soil Biology & Biochemistry 40 (2008) 2660–2669

Contents lists available at ScienceDirect

Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio

Direct experimental evidence for the contribution of lime to CO2 release from managed peat soil Christina Biasi*, Saara E. Lind, Niina M. Pekkarinen, Jari T. Huttunen, Narasinha J. Shurpali, Niina P. Hyvo¨nen, Maija E. Repo, Pertti J. Martikainen University of Kuopio, Department of Environmental Science, Bioteknia 2, P.O. Box 1627, FI-70211 Kuopio, Finland

a r t i c l e i n f o

a b s t r a c t

Article history: Received 22 December 2007 Received in revised form 4 July 2008 Accepted 10 July 2008 Available online 8 August 2008

Liming is a common management practice used to achieve optimum pH for plant growth in agricultural soils. Addition of lime to the soil, however, may cause CO2 release when the carbonates in lime dissolve in water. Although lime may thereby constitute a significant carbon source, especially under acidic soil conditions, experimental data on the CO2 release are lacking so far. We conducted a split-plot experiment within a cut-away peatland cultivated with a bioenergy crop (reed canary grass, Phalaris arundinacea L.) with lime and fertilizer treatments to determine effects of lime on the CO2 emissions from soil and to better understand mechanisms underlying liming effects. Carbon dioxide release was measured over two growing seasons in the field after liming, and complementary laboratory studies were conducted. To differentiate CO2 derived from lime and biotic respiration the d13C of CO2 released was determined and the two-pool mixing model was applied. The results showed that lime may contribute significantly to CO2 release from the soil. In the laboratory, more than 50% of CO2 release was attributable to limecarbonates during short-term incubation. Lime-derived CO2 emissions were much lower in the field, and were only detected during the first (2–4) months after the application. However, a maximum of 12% of monthly CO2 emissions from the cultivated peatland originated from the lime. Biotic respiration rates were similar in limed and unlimed soils, suggesting that higher pH did not, at least in the short-term, increase carbon losses from cultivated peat soils. Additional fertilization and acidification did not contribute to further CO2 release from the lime. According to our first estimations about one sixth of the lime applied would be released as CO2 from the managed peatland, with all lime-derived emissions occurring during the first year of application (equivalent to about 4.6% of the total annual CO2 losses from the soil in the first year). This suggests that the mass-balance approach as proposed by the IPCC Tier 1 methodology, which assumes that all carbon in lime ends up as CO2 in the atmosphere, overestimates the emissions from lime. Our study further shows that there is a great risk to overestimate heterotrophic microbial activity in limed soils by measuring the CO2 release without separating abiotic and biotic CO2 production. Ó 2008 Elsevier Ltd. All rights reserved.

Keywords: CO2 Managed peatlands Bioenergy crops Soil respiration Liming Carbonate dissolution 13 C Partitioning Fertilization IPCC greenhouse gas inventory

1. Introduction Peatlands cover from 3,850,000 to 4,100,000 km2 of the global land area, representing about 3% of the land of the Earth (Gorham, 1991). Despite this relatively small coverage, they have great importance in the global carbon cycle. The total carbon store in peat soils is estimated to range from 202 to 860 Gt (Bohn, 1976; Post et al., 1982) and is thus among the biggest carbon pools globally, exceeding that of forests. Today, however, about 20% of the peatlands in the world are exploited for agriculture, forestry and peat industry. In Finland, 60% of the original peatland area has been

* Corresponding author. Tel.: þ358 17 16 3589; fax: þ358 17 16 3750. E-mail address: christina.biasi@uku.fi (C. Biasi). 0038-0717/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2008.07.011

drained (Finnish Forest Research Institute, 2005). As a result of peatland management the carbon balance changes dramatically. The net ecosystem CO2 exchange of agricultural peatlands is dominated by CO2 release over CO2 uptake due to the combined effects of low water table; mechanical disturbance, e.g., tilling; and fertilization (Lohila et al., 2004; Maljanen et al., 2001a). In 1999, the greenhouse gas emissions from Finnish peatlands used for agriculture were estimated to be 2.5 Tg CO2 equivalents, which is over 3% of all national greenhouse gas emissions (Ministry of the Environment of Finland, 2001). Agriculture is responsible for 10% of total greenhouse gas emissions in Finland, and organic soils are the most important agricultural sources of CO2 and N2O (Ministry of the Environment of Finland, 2001). In Finland, and in many other countries with conventional agriculture, liming is a common management practice. Lime is

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669

added to the soil to neutralize the acidifying effect of the fertilizer and specifically the natural acidity of peat soils in order to achieve optimum pH for plant growth. In the northern countries with predominantly acidic soils, lime is applied at a relatively high rate of about 2–10 t ha1 every 4–5 years, mainly as calcitic limestone (CaCO3) or dolomitic limestone [CaMg(CO3)2]. Carbon dioxide evolves when lime dissolves in water, especially at relatively low pH (Butler, 1982). It has been recognized that the chemical liberation of CO2 from lime can contribute significantly to the CO2 emissions from agricultural soils (e.g. Robertson et al., 2000). Carbon dioxide emissions from the dissolution of lime are generally estimated according to the default methodology of the Intergovernmental Panel of Climate Change (IPCC, 1997), assuming that all carbon in lime applied is released from the soil to the atmosphere. In Finland, the annual emissions due to liming were calculated to be 0.6 Tg CO2 for 2001 (Ministry of the Environment of Finland, 2001). However, the assumption that all of the carbon in lime dissolves as CO2 is currently challenged by some authors (Hamilton et al., 2007; West and McBride, 2005). Emissions can be lower, because when lime dissolves non-gaseous bicarbonate is formed which takes up free CO2, a process that is especially important at neutral or alkaline soil conditions. Further, CaCO3 can be re-precipitated in coastal oceans thereby reducing net emissions. Hamilton et al. (2007), by studying soil solution chemistry and using the carbonate stoichiometry, argued that lime may even act as a carbon sink in certain managed ecosystems. Despite the crucial impact of such effects on the overall carbon balance, the carbon derived from lime is rarely considered in ecosystem carbon balance studies and flux-based measurements. A refinement of the CO2 emissions as a consequence of liming in different soil conditions is needed by providing measurement-based data, in order to reliably estimate which portion of carbon in lime is released to the atmosphere (IPCC, 2006). Although the importance of lime-derived CO2 as a greenhouse gas is not well understood, effects of lime and consequent increase in pH on microbial activity and decomposition of organic matter have been widely studied. Lime is considered to improve soil conditions and thus to increase microbial respiration and loss of soil organic carbon (SOC) as CO2 (Persson et al., 1989; Kreutzer, 1995; Fuentes et al., 2006; Andersson and Nilsson, 2001), but results on effects of lime on CO2 emissions are highly diverse (Martikainen, 1996). Unfortunately little experimental data are available to show the relative importance of chemical and biological CO2 emissions in total CO2 release, and thus to understand the true effects of pH increase on soil carbon turnover. It is impossible to reliably separate lime-borne CO2 from biotic CO2 by conventional methods when measuring soil respiration. However, stable isotope techniques can be used to follow the fate of lime in soil as limestone has a different carbon isotopic signature than C3 plants and soil derived from C3 vegetation. By applying the mixing model, the relative contribution of two sources with different isotopic signatures combined in a mixture can be calculated (Fry, 2006). However, so far, experiments with stable isotopes are scarce. Only one laboratory study using 13C signatures to distinguish between inorganic, lime-derived and organic carbon in CO2 was published (Bertrand et al., 2006), but no field data exist. As part of a larger project on the greenhouse gas balance of reed canary grass (RCG) cultivation on a cut-away peatland, we examined the effects of lime additions on CO2 release from soil. The cultivation of RCG as a bioenergy crop on organic and mineral soils is rapidly expanding in northern Europe. RCG thrives well at low temperatures, has high biomass production capacity including belowground production and is cultivated without tilling over the whole rotation period of 10–15 years. Thus, RCG cultivation holds promise not only to reduce greenhouse gas emissions by serving as

2661

an alternative energy source, but also to sequester atmospheric CO2 into the soils (Parviainen, 2007; Shurpali et al., 2008; Huttunen et al., 2004). To estimate the greenhouse gas balance of a bioenergy cultivation, however, all components responsible for the CO2 exchange have to be taken into account. In this study, we determined the amount and isotopic signature of CO2 released from soil after a liming event over 2 years in field experiments and conducted complementary laboratory experiments. We separated lime-borne CO2 and biotic CO2 with the stable isotope approach to determine the true effects of increase in pH on microbial activity and to quantify the proportion of lime-borne, chemical and biological CO2 emissions in overall CO2 losses. We additionally determined the isotopic composition of the microbial biomass to investigate if the soil microbes used the CO2 derived from lime as a carbon source. Microbial CO2 fixation has been reported previously from soils (Miltner et al., 2005; Santruckova et al., 2005) and thus has to be considered when calculating the isotopic signatures of the end-members in the two source mixing model. Effects of liming were studied with and without treatments of acidifying fertilizer, in order to better understand the underlying mechanism associated with chemical CO2 release. 2. Materials and methods 2.1. Study site The study was conducted within the peatland complex Linnansuo in Tuupovaara in eastern Finland (62 300 N, 30 300 E; 110 m a.s.l.). The study site is situated between the southern- and mid-boreal climatic zones with a mean annual temperature of þ2.1  C and a mean annual precipitation of 669 mm (Drebs et al., 2002). Mean temperature in July is 16  C. The peatland is classified as an ombrotrophic Sphagnum fuscum pine bog and started to develop through primary formation about 10,000 years B.P. (Tolonen, 1967). Like all raised bogs in Finland it initiated as a minerotrophic peatland (Vasander, 1996). The most characteristic peat forming plants within the lower peat layers were Sphagnum subsecundum, Equisetum fluviatile, Carex limosa, Scorpidium scorpioides and Calliergon trifarium, while within the upper peat layers S. fuscum remains are dominant. Ombrotrophication occurred between 3000 and 4000 years B.P., at a peat layer depth of about 1.1 m. The peatland, which overlies sand, has a maximum depth of 3.3 m. The peatland complex Linnansuo before drainage and peat extraction is described in detail by Tolonen (1967). Between 1976 and 1978, selected sectors of the peatland complex were prepared for peat extraction. The vegetation was removed, the surface was leveled and drainage ditches were dug. In 1978, peat extraction began and it is still continuing in the main parts of the cut-away area. In 2001, however, when the residual peat thickness ranged from 20 to 85 cm, 15 ha were abandoned and cultivated with RCG (Phalaris arundinacea L.) for bioenergy production. Prior to cultivation, the field was tilled and drainage ditches were deepened. A low-alkaloid, hardy RCG variety ‘‘Palaton’’ was sown. Every year since then, slow-release fertilizer pellets have been applied at a rate of 350 kg ha1 (N:P:K ¼ 17:4:13). Lime was added as fine-crushed dolomitic limestone [CaMg(CO3)2] at a rate of 7.8 t ha1 during the first year of plantation, and again on May 18 in 2006. The amount of inorganic carbon added during the liming event was thus 101 g C m2. Since RCG is a perennial grass, the cultivated site is not tilled during the rotation period (10–15 years). The yield of the crop, which is harvested in spring to reduce its moisture content and to improve its use as a fuel, was 4.8, 3.7, 2.0 and 3.6 t DM ha1 for the growing seasons 2003, 2004, 2005 and 2006. Mean air temperature between May and September was 13.5 and 13.1  C in 2006 and 2007, respectively, and total precipitation was 249 and 423 mm during the same time period.

2662

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669

2.2. Experimental design The field experiment was arranged in a random split-plot design with five replicates. In spring 2006, before fertilization and liming of the RCG field, five 6  6 m plots, separated from each other by approximately 50 m, were fenced within the 20 m wide RCG strip. Each of the 6  6 plots was subdivided into four 2  2 m subplots, which were either limed (L), fertilized (F), limed and fertilized (LF) or left as untreated controls (C). The subplots were surrounded by 1 m buffer zones without fertilizer or lime. All treatments were laid out on 18 May 2006, and fertilization treatments were repeated on 7 June 2007. To ensure uniform application, lime and fertilizers were applied by hand on the surface soil at the same rate as for the rest of the RCG field (see above). 2.3. Field measurements and gas sampling Measurements of CO2 emission rates and collection of CO2 samples for isotopic analysis were carried out in the field using a closed chamber system, gas-tight syringes (SGE, Australia) and a portable infra-red gas analyzer (LI-6200 Portable Photosynthesis System, LI-COR, Inc., Lincoln, NE, USA). On 27 May just after liming, collars (10 cm diameter) made of thin-walled PVC were inserted 20 cm deep into the soil at each subplot. Aboveground vegetation was removed thereafter, every week throughout the growing seasons and also a day prior to the respiration measurements. The CO2 emitted in situ thus originated from soil respiration including decomposing roots, maintained activity of severed roots and limecarbonates. On 29 May, 16 June and 14 September 2006 CO2 emission rates were measured and CO2 samples were taken for determination of d13C of CO2. Measurements were repeated on 3 May, 7 June, 4 July, 16 August and 30 October 2007. An opaque respiration chamber (1.2 l) was fitted over the collar to form an airtight seal and to create a headspace over the soil surface. The IRGA was connected to the chamber through a rubber septum at the top of the chamber, which also allowed syringe sampling for d13C of CO2. At measurement times, the chamber was placed gently over the collar and the air from the headspace was pumped through the IRGA and back to the chamber at a flow rate of about 300 ml min1. Data on CO2 concentration were recorded at 10 s intervals for 12 min, after the noise resulting from disturbances during fixing the chamber subsided (usually after 10–20 s). After 2, 4, 6, 8 and 12 min, 1 ml of the headspace air was removed with an airtight glass syringe and immediately transferred into exetainer vials (Exetainer, Labco). These vials were evacuated and flushed with N2 in the lab prior to sampling. After termination of the measurements the ambient and chamber temperatures were measured. The CO2 efflux was calculated from the linear increase in CO2 concentration in the chamber over the measurement period. The isotopic signature of CO2 released was determined as described below. 2.4. Laboratory experiments On 12 July 2006 (a day representing the peak growing season), soil samples were taken for the laboratory experiments. A soil core was collected from the 0–10 cm depth from the center of each subplot (C, F, L, LF) using a metal soil corer (diameter 7 cm). The soil samples were stored at þ4  C for 1 week until further processing. For processing, the peat was carefully sieved (3.35 mm mesh size) and the roots were removed by sieving and by hand picking. Peat pH was measured (WTW pH 340) at room temperature after mixing a subsample of the soil with distilled water at a ratio of 1:1.7. The water content of the soil samples was determined from 10 g of fresh soil on an oven dry-weight basis (60  C). The dried soil samples were homogenized in a mill (A10 Yellow Line, IKA Works Inc.) until a fine powder for analysis of %C, %N and d13C. The content

of total soil organic matter (SOM) was determined by loss on ignition at 450  C. Laboratory incubation experiments were performed at standard conditions (15  C, 60% water holding capacity; WHC) to determine soil respiration rates and to collect CO2 for d13C analysis. From each of the soil samples, 15 g of fresh soil was weighed into 500 ml glass bottles and water was added to reach 60% WHC. No additional lime was added during the laboratory incubations. The bottles were left open (covered with aluminum foil) over-night at 15  C. After flushing the incubation bottles with ambient air for 15 s, they were sealed with rubber septa and screw caps and 60 ml of ambient air was added to increase internal gas volume for sampling. Gas samples were taken after 20, 60, 120, 240 and 360 min. Each time two samples were taken: (1) a 10 ml subsample by a polypropylene syringe equipped with a three-way stopcock for CO2 concentration analysis and (2) a 1 ml subsample by an airtight glass syringe for isotopic analysis, transferred into a pre-evacuated, N2-flushed exetainer vial. The CO2 concentration was analyzed during the same day by Hewlett Packard 5890 Series II gas chromatograph equipped with a thermal conductivity detector (TCD) for CO2 (Nyka¨nen et al., 1995). The CO2 production rates were calculated from the linear increase in CO2 concentration during the measurement period. The isotopic signature of CO2 released was determined as described below. Collection of soil samples was repeated on 17 August 2007 for pH measurements. Soil sampling and pH measurements followed the same procedure as in 2006 (see above). 2.5. Total C and d13C of microbial biomass Microbial biomass was estimated using the chloroform fumigation extraction method modified after Vance et al. (1987). A subsample (10 g) of fresh soil was fumigated with ethanol-free chloroform in a desiccator for 24 h, extracted with distilled water (50 ml) and filtered twice, first through an ashless Whatman filter (Whatman 589/3; 2 mm) and then through a sterilized polyethersulfone filter (Supor-200; 0.2 mm). The same extraction procedure was also performed for non-fumigated soil. All extracts were deep-frozen before further processing. Total organic carbon (TOC) in the extracts was analyzed on a TOC analyzer (TOC-VCPH, Shimadzu) at the University of Vienna (Austria). Microbial biomass carbon was calculated as the difference in carbon extracted from the fumigated and non-fumigated soils. A conversion factor of 0.45 (Wu et al., 1990) was used to estimate microbial C. A subsample (20 ml) of the extracts was freeze-dried and weighed into tin cups for stable isotope analysis. 2.6. Stable isotope analysis The d13C of CO2 from both field and laboratory studies was analyzed by a continuous-flow isotope ratio mass spectrometer (IRMS; Thermo Finnigan DELTA XPPlus, Bremen, Germany) coupled with a Trace GC and a Precon interface within 4 days after sampling. Separation of CO2 from N2O was performed with a Pora PLOT Q column (27.5 m length; 0.32 mm i.d.; Varian) at 25  C using He as carrier gas. Sample loading and injection were done with a sample loop swept by the carrier stream using PAL autosampler (Thermo Finnigan, Bremen, Germany). Each sample measurement cycle was started with three reference gas injections. The isotopic values are expressed relative to the Vienna-Pee Dee belemnite (V-PDB) reference as d13CV-PDB:

d13 CV-PDB ð&Þ ¼



 Rs  1  1000 Rr

Where R is the 13C/12C ratio and subscripts s and r indicate sample and reference, respectively. The external analytical precision of the

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669

d13C measurements was 0.15& based on repeated measurements of a laboratory working standard (n ¼ 10). The d13C, %C and %N of the soil samples and the d13C of lime and microbial biomass carbon were analyzed by using the IRMS described above interfaced with an elemental analyzer (Flash EA 1112 Series, Thermo Finnigan, Bremen, Germany) via the open split interface (Conflow III, Thermo Finnigan, Bremen, Germany). External precision was 0.16& for the stable isotopic analysis and 0.9% for elemental analysis (n ¼ 10). 2.7. Calculations The d13C of CO2 released was calculated using the Keeling Plot approach (Keeling, 1958), by relating the d13C of the CO2 accumulated in the headspace to the inverse of its concentration. Data on CO2 concentration were obtained from IRGA measurements (field) or from gas chromatographic analysis (laboratory). The intercept on the y-axis of the linear regression (the Keeling Plot intercept) shows the isotopic composition of the released CO2. To achieve high confidence in the d13C values of CO2 efflux (Pataki et al., 2003), intercept results were only accepted when the standard deviation of the intercept was <0.8&, when the regression coefficient was 0.95, when a minimum of four data points was included, and when the range in CO2 concentration accumulated was >100 ppm. Outliers were excluded from further analysis, but more than 90% of the results matched the given quality criteria. The fractional contribution of CO2 derived from lime to total carbon content and from lime-borne CO2 to overall CO2 emissions was calculated following the two-pool mixing model:

2663

the sand, which was randomly spread over the field when the drainage ditches were initially dug and later deepened. The carbon and nitrogen contents of the soil were therefore also highly variable, ranging from an average of 2 to 3.7 g kg1 soil and from an average of 0.05 to 0.14 g kg1 soil between the treatments, respectively. All results from laboratory incubations are thus expressed on a soil organic matter basis. The C/N ratio of the peat was on average 38.6 with no differences between the treatments, but deviations were again relatively high (Table 1). The d13C of the bulk soil ranged between 27.0 and 27.4& (Table 1), while the lime exhibited the expected positive isotopic signature of 2.1&. Although the bulk soil in the limed plots was slightly enriched in 13C compared to the unlimed ones, indicating the presence of lime, the difference was not statistically significant. In the year of lime application (2006), the pH was higher in limed compared to non-limed plots (P  0.05). In the second year after lime application (2007), the difference in pH between limed plots and other treatments was still detected, but it was not statistically significant (Table 1). Fertilization significantly decreased soil pH in 2007 (P  0.05). 3.2. CO2 emissions in the field

3. Results

In 2006, soil CO2 emission rates of control plots increased from 321 mg m2 h1 in May to 432 mg CO2 m2 h1 in June, with no differences between fertilized, limed and limed þ fertilized plots on either sampling occasions (Fig. 1). The lowest flux was measured in September 2006. In May, shortly after the lime application, the d13C of CO2 was significantly more positive in limed plots, reflecting the contribution of lime to CO2 emissions (Table 2, P  0.01). The average shift in d13C values was 3.9&. As calculated by the mixing model, 19 and 12% of the soil CO2 was derived from the lime in limed and limed þ fertilized plots, respectively. The biotic respiration, resulting from the difference between total flux and lime-borne flux, was not significantly different from the unlimed plots (Fig. 1). Fertilization decreased the d13C of CO2 respired (Table 2). By June, the d13C values in limed plots were still elevated compared to control plots, but the average shift had decreased to 2.5& (Table 2). This demonstrates a relatively decreasing impact of lime on CO2 emissions. Nevertheless, on average 8% of soil CO2 emissions were still then attributable to the dissolution of lime. In September 2006, when data were only collected from fertilized and limed þ fertilized plots, the isotopic signatures between fertilized and limed þ fertilized plots converged, indicating that there was no impact of lime on CO2 efflux. No significant interactions between lime and fertilizer were found in any month, indicating that these effects were independent of each other. In 2007, CO2 emissions were higher than in 2006 (Fig. 2). This resulted from the exceptionally dry summer of the year 2006, which most likely limited microbial respiration. Mean CO2 emissions in 2007 were highest in June and July, and lowest in September. There were no effects of liming or fertilization on CO2 emission in 2007, although there was a significant treatment interaction in May (P  0.05; Fig. 2). The cumulative CO2 emissions were estimated by integrating the emission rates linearly between the monthly measurements and summing over the 2007 growing season. Emissions ranged between 1320 and 2120 g CO2 m2, and did not differ significantly between the treatments. The d13C values of CO2 respired were also similar between the treatments in each month (Table 2). Thus, according to the isotope mass-balance approach, lime did not contribute any more to overall CO2 emissions in the second year after application.

3.1. Soil characteristics

3.3. Laboratory incubations

Mean organic matter content of the soil samples ranged from 42 to 63% between the treatment (Table 1). The variation was due to

The application of lime increased soil CO2 release in the laboratory experiments. CO2 production rates ranged between 10 and

f ¼

ðd  d 0 Þ ðd1  d0 Þ

where d is the isotopic signature of C (for soil) and CO2 respired (for gas) of limed plots, d0 are the respective isotopic signatures for unlimed plots, and d1 is the isotopic signature of lime. The mixing model applies under the assumption that the d13C of CO2 respired from biological sources in unlimed plots is equal to that in limed plots and that an isotopic equilibrium between the lime-carbonates and CO2 derived from lime exists. The d13C of microbial biomass was estimated as follows:



d13 CMB ð&Þ ¼

d13 C  Cf  d13 C  Cnf f



Cf  Cnf



nf

where Cf and Cnf are amounts of carbon (mg C g1 SOM) and d13Cf and d13Cnf are the carbon isotopic signatures (&) of extracts from fumigated and non-fumigated soils, respectively. 2.8. Statistical analysis Effects of liming and fertilization treatments on respiration rates, d13C of respiration and soil properties and possible interactions were tested by using two-way ANOVA analysis including effects of lime and fertilization as main factors. Significant treatment effects are reported at *P  0.05, **P  0.01, ***P  0.005. Statistical analysis was performed with SPSS 14.0 for Windows (Chicago, Illinois).

2664

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669

Table 1 Soil characteristics of cut-away peat cultivated with reed canary grass as a bioenergy grass and treated as follows: control (C), fertilized (F), limed (L), limed and fertilized (LF) Treatment

SOM (%)

C/N

pH

pHa

d13C of SOC (&)

C F L LF

63.0  8.9 47.1  13.0 41.5  9.4 56.9  19.1

40.0  2.8 38.8  2.4 38.6  3.5 37.0  1.7

4.87  0.10 4.92  0.16 5.29  0.24 5.20  0.23

4.61  0.22 4.51  0.21 5.00  0.06 4.45  0.12

27.2  0.1 27.4  0.2 27.0  0.1 27.1  0.2

Source of variation L F LF

NS NS NS

NS NS NS

* NS NS

NS * NS

NS NS NS

Data are means  SE (n ¼ 5). Below: results from two-way ANOVA analysis (*P  0.05; NS ¼ no significance). a Data from 2007, when only fertilizer was applied; all other data are from 2006, when the treatments were laid out.

37 mg CO2 g1 SOM h1 (Fig. 3). They were 2.6–2.8-fold higher in the limed and limed þ fertilized soils compared to the control and fertilized soils, respectively (P  0.001). The d13C values of CO2, which were significantly more positive in the soils receiving lime (Fig. 3), showed clearly that CO2 in limed soils derived not only from carbon mineralization by microbes, but also from lime. The isotopic values increased, on average, by 16&, with slightly, but nonsignificantly higher shifts within the limed þ fertilized plots than within the limed plots. We calculated by using the mixing model that 53% of the CO2 evolution from the limed soils and 70% from the limed þ fertilized soils derived from the dissolution of the added carbonate during this short-term laboratory incubation experiment. The residual, biotic respiration, which was estimated as the difference between total flux and lime-borne flux, was similar across all treatments (Fig. 3). Soil microbial biomass carbon and dissolved organic carbon, which ranged from 0.9 to 2.2 and from 1.2 to 1.5 mg C g1 SOM, respectively, showed no differences between the treatments (Table 3). The use of water to extract soil microbial biomass resulted in relatively lower amounts of carbon compared to the commonly used K2SO4 (N. Pekkarinen, unpublished observations). This was necessary to avoid interference of the salt during the stable isotope analysis (Potthoff et al., 2003). However, liming had no effect on the size of microbial biomass and dissolved organic carbon. The d13C values of microbial biomass were also similar between limed and unlimed plots (Table 3), indicating no uptake of lime-derived CO2 by the microbial biomass. The isotopic signature of dissolved organic carbon showed no increase due to liming. On the contrary, fertilization significantly decreased the d13C values of dissolved organic carbon (P  0.05). No interaction effects of liming and fertilization were found on the microbial biomass carbon and DOC. 4. Discussion Our results show that agricultural lime applied to cultivated peat soil contributes to CO2 emissions. Both in field and laboratory studies, lime-derived carbon was found in CO2 released from soils. This is the first direct experimental evidence for the rate of limeborne CO2 release in situ within managed soils. The effect was short-lived in the field, and due to the high overall variation in soil respiration in the field measurements this effect would have been difficult to demonstrate without the sophisticated, isotopic method separating CO2 from lime and soil respiration. The proportion of lime-borne CO2 to overall CO2 release was especially striking within the laboratory experiments. Carbon dioxide efflux increased by 2.8 times as a consequence of liming. Without correction for the abiotic lime contribution to overall respiration, the effects of lime would have been falsely interpreted as increased microbial respiration. Instead, our calculations based on the differences in the isotopic signatures of lime and microbial respiration showed that the largest part of CO2 (53–70%) originated from the lime. These high lime-derived CO2 emissions occurred

although no additional lime was added to the incubated peat soil, suggesting that the potential for abiotic CO2 release is also high at field conditions (see discussion below). Thus, in acidic peat soils carbonate-carbon in lime may convert largely to CO2. The contribution of lime to total CO2 release was only marginally higher within limed þ fertilized compared to limed plots, suggesting that the fertilizer did not contribute to further CO2 release from the lime. Bertrand et al. (2006) showed in laboratory experiments with alkaline and limed soils that up to 35% of overall respiration was derived from the lime-carbonates. The relatively higher limederived CO2 in our experiments may be due to the acidity of peat soils and the consequently higher rate of lime dissolution. The residual biotic respiration rates were similar between all treatments. Thus, at least within the short-term, the higher pH did not increase decomposition and thereby carbon loss from the soil organic matter within the cultivated peat. Lime-derived CO2 was also detected in the field, but only during the year of lime application. The proportions of lime-borne CO2 to overall CO2 emissions were lower in the field compared to the laboratory, but still significant in the 2 months after application. We attribute the relatively higher impact of lime in the laboratory mostly to the addition of water addition to adjust the soils to standard laboratory conditions (60% water holding capacity). The lime-carbonates dissolve in water which evidently causes abiotic CO2 release from acidic peat soils, mimicking effects of rain events. The effect of lime on CO2 emissions might have been also diluted in the field due to the higher contribution of peat respiration originating from the entire peat column while only the upper 10 cm were used for the laboratory experiment, and due to the higher contribution of roots in the field which could have been still alive after trenching (Shurpali et al., 2008). However, in May, shortly after the application of the lime, a highly significant amount of 12% of the CO2 emitted from the soils originated from the carbonates in limed þ fertilized plots, reflecting the usual management practice in the field. The absolute emissions derived from lime were even higher in June, although the relative proportion to soil respiration decreased (Fig. 1, Table 2). The contribution of lime to overall CO2 release most likely leveled out during the very dry summer months of the year 2006. Indeed, in September 2006, no lime-borne CO2 was detected. Contrary to the laboratory experiment, fertilization apparently decreased the dissolution of lime after application, but this was due to lower d13C values of biotic respiration after fertilization (Table 2). It is possible that nutrient additions changed the substrate utilization patterns of microbes leading to altered isotopic composition of CO2 respired (Bowling et al., 2008; Biasi et al., 2005). In 2007, the second year after lime application, no contribution of limecarbonates to CO2 emissions was observed. Thus, the dissolution of lime in acidic peat soils is rapid and occurs during the year of lime application. The field experiments confirmed the laboratory findings, that liming, irrespective of fertilization, has no effects on microbial respiration and thus peat decomposition.

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669

1800

mg CO2m-2 h-1

1500

May

Biotic CO2 Abiotic CO2 (Lime-borne)

1200 900 600

19

12

300 0 1800

June

mg CO2m-2 h-1

1500 1200 900 600

8.8

6.8

300 0 1800

September

mg CO2m-2 h-1

1500 1200 900 600 300 0

n.a.

C

n.a.

F

L

LF

Fig. 1. Soil CO2 emission rates of peat soils (in situ) cultivated with a bioenergy crop. Measurements were taken in May, June and September 2006 after fertilization (F), liming (L) and liming þ fertilization (LF). Control plots were left untreated (C). The percentage of lime-borne CO2 in total CO2 emissions from soils, indicated by numbers above the bars, was calculated by applying the mass-balance approach (see text). The y-axis is constant for all graphs in Figs. 1 and 2 to compare flux rates between 2006 and 2007. Differences between the treatments were not significant (two-way ANOVA; P  0.05). n.a., Not analyzed. Data are means  SE (n ¼ 3).

Effects of liming on microbial activity and mediated increase in pH are diverse in managed soils. In forest and grassland soils, where lime is added to counteract the acidifying effect of the fertilizer, most studies show increased respiration rates, microbial activities and decomposition rates (Aarnio et al., 2003; Andersson and Nilsson, 2001; Fuentes et al., 2006; Kemmitt et al., 2006; Lorenz et al., 2001; Martikainen, 1996; Rosenberg et al., 2003; Kreutzer, 1995), but negative or no effects have also been reported (Johnson et al., 2005). Possible underlying mechanisms of positive effects include increased substrate availability (Andersson and Nilsson,

2665

2001), higher microbial biomass and functional changes in the soil microbial community (Fuentes et al., 2006). Within natural acidic peatlands, negative, little or no effects of liming on carbon mineralization were shown (Chapin et al., 2003; Keller et al., 2005; Bridgham and Richardson, 1992). On the contrary, liming has also increased CO2 production in some peat soils (Murakami et al., 2005). Different ecosystems seem to respond differently to liming, with soil processes in peat most likely being less limited by low pH, and short-term effects seem to differ from long-term effects. However, it has to be noted that irrespective of the ecosystem studied and effects of the lime, the carbonate itself as a potential source of CO2 has rarely been taken into account and is only sometimes discussed (Fuentes et al., 2006; Murakami et al., 2005; Bertrand et al., 2006). According to our studies, lime-borne CO2 emissions can be large enough to confound the interpretation of the results on microbial activity. For measuring effects of lime on respiration, thus the separation of biotic from abiotic CO2 fluxes is essential. Separating sources of respiration by stable isotopic techniques has generally proven to be a powerful method in ecosystem studies (Kuzyakov, 2006; Trumbore, 2006; Midwood et al., 2006). However, it is based on several assumptions, e.g. that the isotopic signatures between the contributing sources differ significantly and that they are known. Thus, the interpretation of our results would not have been that straightforward, if we had found evidence for microbial utilization of CO2 derived from lime. Microbial CO2 fixation would have confounded the isotopic signal of heterotrophic respiration, which we assumed to be similar to the non-limed soils. Generally, a wide range of soil microorganisms can fix CO2, including chemoautotrophs, photoautotrophs and both anaerobic and aerobic heterotrophs (Schlegel, 1985). The importance of microbial CO2 fixation within the overall ecosystem carbon balance is, however, believed to be low. Nevertheless, some authors have found that a considerable proportion of the microbial biomass originates from CO2 (Miltner et al., 2005; Santruckova et al., 2005), suggesting a critical role of microbial CO2 assimilation in soil carbon transformation processes. In our experiment, any heterotrophic fixation of carbonate CO2 could be ruled out, since no differences in d13C values of microbial biomass were found as a consequence of liming. The d13C value of DOC was even more positive in fertilized plots which could result from the changed substrate utilization pattern under better soil nutrient status as discussed above. However, most likely the importance of microbial CO2 fixation is small at relatively low pH, since microbes do not take up CO2 as a gas but utilize bicarbonate, which is less abundant at acidic soil conditions (Santruckova et al., 2005; see discussion below). Generally, the d13C of respiration from both field and laboratory studies was more positive than the d13C of soil organic carbon (Table 1). It was found in many studies that the d13C of respiration is enriched (by >2&) compared to that of the bulk organic material as recently reviewed by Bowling et al. (2008). However, similar isotopic composition of CO2 respired and soil organic carbon was reported (Stevenson and Verburga, 2006; Stevenson et al., 2005; Bertrand et al., 2006). A higher d13C value of CO2 relative to soil organic carbon may be explained by the use of more labile carbon compounds of the soil microbes, which are often more enriched in 13 C compared to the bulk soil (Bowling et al., 2008; Crow et al., 2006; Biasi et al., 2005). But also biochemical fractionation or microbially derived carbon, which is often enriched in 13C, is discussed as mechanisms behind the observed pattern (Bowling et al., 2008). A complete understanding of the differences in carbon isotopic signatures between pools and CO2 fluxes is, to our knowledge, lacking so far. The absolute, annual carbon losses derived from the lime in 2006 were calculated by roughly assuming an exponential decrease between the day of application and the measurements taken in

2666

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669

Table 2 Effects of liming and fertilization on the d13C values of CO2 released from soil of cultivated peatlands (in situ) over the growing seasons of 2006, when all treatments were laid out, and 2007, the second year after liming Year

Treatment

2006

C F L LF

d13C of CO2 (&)

Sources of variation L F LF 2007

C F L LF

Sources of variation L F LF

May

June

21.9  0.3 23.0  1.0 17.5  0.4 19.7  0.3

25.3  0.3 25.3  0.5 22.9  1.0 22.8  0.6

July

August

September n.a. 25.2  0.6 n.a. 26.1  0.4

October

** * NS

** NS NS

NS

21.2  0.8 22.1  0.6 21.1  0.9 22.5  0.4

21.1  1.0 21.5  0.4 20.9  0.8 21.5  0.3

23.9  0.6 22.7  0.6 21.7  1.1 23.6  1.0

23.5  0.2 24.1  0.5 23.1  0.6 22.8  0.8

24.0  1.0 23.1  1.0 22.8  0.8 23.1  1.8

NS NS NS

NS NS NS

NS NS NS

NS NS NS

NS NS NS

Data are means  SE (n ¼ 3–5). Below: results from two-way ANOVA analysis (*P  0.05; **P  0.01; NS ¼ no significance). Abbreviations are according to Table 1. n.a., Not analyzed.

FxL*

Biotic CO2

May

August

1500

1500

1200

1200

900

900

600

600

300

300 0

0 1800

June

October

1800

1500

1500

1200

1200

900

900

600

600

300

300

0

C

1800

F

L

LF

mg CO2m-2h-1

mg CO2m-2h-1

1800

mg CO2m-2h-1

mg CO2m-2h-1

1800

0

July

mg CO2m-2h-1

1500 1200 900 600 300 0

C

F

L

LF

Fig. 2. Soil CO2 emission rates of peat soils (in situ) cultivated with a bioenergy crop. Measurements were taken in May, June, July, August and October 2007. No abiotic (lime-borne) CO2 efflux was detected in the second year after lime application. Abbreviations are according to Fig. 1. Data are means  SE (n ¼ 4–5). Significant treatment effects are shown (twoway ANOVA, *P  0.05).

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669

10 L

a

***

13C

0 -10 -20 -30

Biotic CO2 Abiotic CO2 (Lime-borne)

µg CO2 g-1 SOM h-1

40

L

***

70

b

53 30

20

10

0

C

F

L

LF

13

Fig. 3. The d C values of CO2 emitted (a) and the CO2 efflux rates (b) from laboratory incubations with cultivated peat soils. The percentage of lime-borne CO2 in total CO2 efflux, indicated by numbers above the bars, was calculated by applying the massbalance approach (see text). Data are means  SE (n ¼ 5). Abbreviations are according to Fig. 1. Significant treatment effects are shown (two-way ANOVA, ***P  0.005). There were no significant differences in the biotic respiration rates among all treatments.

2006 and summing up the emission rates (Kreutzer, 1995). According to this first approximation, a sum of 15.4 g CO2C m2 y1 was emitted as a consequence of liming in 2006 (equivalent to 15.2% of the amount of lime-carbonates added). The annual total soil CO2 emissions from the study site were estimated including additional 20 measurement points in 2006 (data not shown) as 336 g CO2-C m2. Thus, about 4.6% of the total soil CO2 emissions resulted from the lime. This is a relatively small, but not negligible component of the annual soil carbon efflux. Other reported values on annual soil CO2 losses of peatlands used for agriculture and organic croplands in Finland range between 392 and 1120 g CO2-C m2 (Nyka¨nen et al., 1995; Maljanen et al., 2001b, 2004). Assuming similar lime-derived emission rates for all study sites, 1.4–3.9% may account for lime within the year of application. Again, lime-derived CO2 may thus be small, but can be significant depending on the magnitude of biotic CO2 losses. The net

Table 3 Effects of liming and fertilization on the concentration and isotopic signature of microbial biomass carbon (MBC) and dissolved organic carbon (DOC) in cut-away peat cultivated with a bioenergy crop Treatment C F L LF

MBC (mg g1 SOM)

d13C of MBC (&)

DOC (mg g1 SOM)

d13C of DOC (&)

0.92  0.21 2.21  1.16 1.06  0.35 1.50  0.85

25.3  0.6 26.3  0.2 25.0  0.4 25.0  1.0

1.42  0.11 1.15  0.36 1.37  0.30 1.49  0.41

26.9  0.1 26.4  0.1 26.9  0.2 26.8  0.2

NS NS NS

NS NS NS

NS * NS

Sources of variation L NS F NS LF NS

Data are means  SE (n ¼ 5). Below: results from two-way ANOVA analysis (*P  0.05; NS ¼ no significance). Abbreviations are according to Table 1.

2667

ecosystem carbon balance is determined by both carbon losses through respiration and carbon uptake through plants. It remains open, whether the growth of RCG increases as a result of liming and whether this increased biomass can offset the CO2 losses associated with the dissolution of lime. There are only few national reports on the proportion of lime to overall CO2 emissions from agricultural soils. Canada, for example, estimated annual CO2 emissions from lime to be 0.3 Mt and concluded that this source is of minor importance in the overall greenhouse gas balance (Canada, 2002). On the contrary, in a report on Brazilian agricultural soils the summarized annual CO2 emissions from lime represented about 10.5% of the total emissions (Bernoux et al., 2003). According to the Tier 1 approach of the IPCC 2006 Guidelines for National Greenhouse Gas Inventories (IPCC, 2006), lime emissions are currently calculated with the mass fraction of carbon in lime, equivalent to 100% carbon emissions in the form of CO2, if countryspecific emission factors are lacking. In our case, within the first year of lime application on cut-away peatland cultivated with RCG, 15.4 g C m2 were released as CO2 from lime. Since no lime-derived CO2 emissions were detected in the second year after application, this amount represents the total sum of inorganic CO2 release from soils. Thus, 15.2% of the carbon in lime applied was released in total as CO2. This is a conservative estimate since ditches, which are an important storage and conduit of run-off water from the field, are not taken into account. However, lateral transport of inorganic carbon might not cause dramatic degassing of lime-borne carbon from ditches, since movement of bicarbonate in humic soils is low (Kreutzer, 1995). Additionally, no differences in d13C of CO2 released from the ditches of the RCG cultivation and adjacent, unlimed peat harvesting areas were detected at least when measured in October 2006 (data not shown). The conclusion of West and McBride (2005) and of Hamilton et al. (2007) that not all carbon in lime ends up as CO2 is based on the assumption that non-gaseous bicarbonate is permanently formed when lime dissolves, which is a process that takes up CO2. However, at pH lower than 5, bicarbonate is not stable and thus its contribution in soils is assumed to be negligible (Butler, 1982). As a first approximation, thus, we estimate the fraction of carbon lost from lime in managed peat soils to be around 15%, although the exact amount remains uncertain given the low number of data acquired. We might have for example missed some abiotic CO2 emissions, for example after rain events (as demonstrated by the laboratory experiment), but these should have been of minor importance since 2006 was an exceptionally dry year. Even considering potential errors in our preliminary estimate, the emission factor of 100% of carbon for calculating the greenhouse gas emissions associated with liming seems to be unrealistic even for acidic peat soils. Our results are in agreement with other authors (Hamilton et al., 2007; Oh and Raymond, 2006; West and McBride, 2005), who concluded that using the default emission factor based on the mass-balance approach may lead to systematic biases of estimates on lime-derived CO2. It is beyond the scope of this study to reveal the full fate of lime in soil, run-off water and downstream water bodies after application. The somewhat higher pH in limed plots in 2007 may indicate that the buffering capacity of lime was not exhausted after 2 years, but a similar increase in pH was not detected in limed soils with fertilizer additions and no lime-borne CO2 was detected in either case in this year. It could be that some part of lime accumulates on the soil surface, as indicated by the slightly increased d13C values of SOC in limed plots (equivalent to the maximum shift in d13C shift which would occur if all lime remains in the soil) or that lime does not disappear by dissolution of carbonates but is transformed into exchange buffer (Kreutzer, 1995). Our study revealed that only about one sixth of the lime applied to managed peat soils can be found in CO2. But more studies need to be conducted to close the mass balance of the lime applied, including analysis of inorganic carbon in soil and

2668

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669

possible lateral transport by wind and water. To develop realistic emission factors, further, a better understanding of storage, transportation and transformation of inorganic carbon and Ca2þ and Mg2þ in lime is needed. 5. Conclusion This study shows for the first time CO2 emissions derived from lime applied to arable soils in field conditions. By applying stable isotopic techniques, we proved that lime may act as a significant carbon source in managed peatlands. The lime-carbonates accounted for up to 12% of monthly CO2 emissions after application, and complementary laboratory studies showed that the potential of CO2 release from lime is even larger. Although annual lime-derived CO2 emissions were relatively small (4.6% of total CO2 release) and only detected in the year of application, biotic respiration rates may be temporarily overestimated by flux-based studies, while the greenhouse gas potential of agricultural soils may be underestimated if the contribution of lime is not considered. The IPCC default emission factor of 100%, however, which assumes that all carbon in the lime is emitted as CO2 to the atmosphere, has to be used with caution, since this approach may overestimate lime emissions as demonstrated here. More direct measurements are needed from different limed soils and watersheds from different countries to verify the deviation from this rule and quantify the proportion of lime released as CO2 to the atmosphere. We suggest to incorporate stable isotope analysis of CO2 within carbon balance studies particularly in countries where liming is an important source, such as Finland, to separate lime-borne CO2 from biotic CO2 for the calculation of CO2 emissions from lime. This allows developing higher Tier methods and country-specific CO2 emission factors for liming (IPCC, 2006). Acknowledgements We thank Jorma Nuutinen, Marko Kuronen, Mirja Heinonen and Tatiana Trubnikova for assistance in field and laboratory work and Andreas Richter and Nina Hinko for support with the DOC analysis. Many thanks also to the Mekrija¨rvi Research Station (University of Joensuu, Eastern Finland) for their co-operation and to Matti Turpeinen (Vapo Ltd.) for excellent support. We are further grateful to Stephen Hamilton for valuable discussion on carbonate dissolution. This study was supported by the Finnish Funding Agency for Technology and Innovation (Tekes), Vapo Ltd., Turveruukki Ltd., Pohjolan Voima Ltd., Kuopion Energia, Savon Voima Lampo¨ Ltd., the Environmental Risk Assessment Center (ERAC), the European Regional Development Fund, the Maj and Tor Nessling Foundation, the Finnish Graduate School in Environmental Science and Technology (EnSTe) and a grant from the Finnish Cultural Foundation (North Savo Foundation). We thank Hannu Koponen for a review of an earlier version of the manuscript and two anonymous reviewers for their constructive comments and suggestions. References Aarnio, T., Ra¨ty, M., Martikainen, P.J., 2003. Long-term availability of nutrients in forest soil derived from fast- and slow-release fertilizers. Plant and Soil 252, 227–239. Andersson, S., Nilsson, S.I., 2001. Influence of pH and temperature on microbial activity, substrate availability of soil-solution bacteria and leaching of dissolved organic carbon in a moor humus. Soil Biology & Biochemistry 33, 1181–1191. Bernoux, M., Volkoff, B., da Conceicao, M., Carvalho, S., Cerri, C.C., 2003. CO2 emissions from liming of agricultural soils in Brazil. Global Biogeochemical Cycles 17 (2), 1049, doi:10.1029/2001GB001848. Bertrand, I., Delfosse, O., Mary, B., 2006. Carbon and nitrogen mineralization in acidic, limed and calcareous agricultural soils: apparent and actual effects. Soil Biology & Biochemistry 39, 276–288. Biasi, C., Rusalimova, O., Meyer, H., Kaiser, C., Wanek, W., Barsukov, P., Junger, H., Richter, A., 2005. Temperature-dependent shift from labile to recalcitrant

carbon sources of arctic heterotrophs. Rapid Communications in Mass Spectrometry 19, 1401–1408. Bohn, H.L., 1976. Estimate of organic carbon in world soils. Soil Science Society of America Journal 40, 468–470. Bridgham, S.D., Richardson, C.J., 1992. Mechanisms controlling soil respiration (CO2 and CH4) in southern peatlands. Soil Biology & Biochemistry 24, 1089–1099. Bowling, D.R., Pataki, D.E., Randerson, J., 2008. Carbon isotopes in terrestrial ecosystem pools and CO2 fluxes (Tansley Review). New Phytologist 178, 24–40. Butler, J.N., 1982. Carbon Dioxide Equilibria and Their Applications. Addison-Wesley Publishing Company, Reading, Massachusetts, 259 pp. Canada, 2002. Canada’s Greenhouse Gas Inventory, 1990–2000. Greenhouse Gas Division Environment Canada, Ottawa, Ontario, 138 pp. Chapin, C.T., Bridgham, S.D., Pastor, J., Updegraff, K., 2003. Nitrogen, phosphorus, and carbon mineralization in response to nutrient and lime additions in peatlands. Soil Science 168, 409–420. Crow, S.E., Sulzman, E.W., Rugh, W.D., Bowden, R.D., Lajtha, K., 2006. Isotopic analysis of respired CO2 during decomposition of separated soil organic matter pools. Soil Biology & Biochemistry 38, 3279–3291. Drebs, A., Nordlund, A., Karlsson, P., Helminen, J., Rissanen, P., 2002. Climatological Statistics of Finland, 1971–2000. Report. Finnish Meteorological Institute, Helsinki, 95 pp. Finnish Forest Research Institute, 2005. Finnish Statistical Yearbook of Forestry. Finnish Forest Research Institute, Helsinki, 421 pp. Fry, B., 2006. Stable Isotope Ecology. Springer, New York, 308 pp. Fuentes, J.P., Bezdicek, D.F., Flury, M., Albrecht, S., Smith, J.L., 2006. Microbial activity affected by lime in a long-term no-till soil. Soil and Tillage Research 88, 123–131. Gorham, E., 1991. Northern peatlands – role in the carbon cycle and probable responses to climate warming. Ecological Applications 1, 182–195. Hamilton, S.K., Kurzman, A.L., Arango, C., Jin, L., Robertson, G.P., 2007. Evidence for carbon sequestration by agricultural liming. Global Biogeochemical Cycles 21, GB2021, doi:10.1029/2006GB002738. Huttunen, J.T., Nyka¨nen, H., Martikainen, P.J., Shurpali, N.J., 2004. Reed canary grass cultivation on cut-away peatlands and the ecosystem carbon balance. In: Pa¨iva¨nen, J. (Ed.), Proceedings of the 12th International Peat Congress. Wise Use of Peatlands, vol. 2. International Peat Society, Jyva¨skyla¨, Finland, pp. 977–982. IPCC, 1997. Revised, 1996. IPCC Guidelines for National Greenhouse Gas Inventories: Reporting Instructions, 3 vols.. IPCC/OECD/IEA, Paris. IPCC, 2006. IPCC Guidelines for National Greenhouse Gas Inventories: Agriculture, Forestry and Other Land Use, vol. 4. IPCC/OECD/IEA, Japan. Johnson, D., Leake, J.R., Read, D.J., 2005. Liming and nitrogen fertilization affects phosphatase activities, microbial biomass and mycorrhizal colonisation in upland grassland. Plant and Soil 271, 157–164. Keeling, C.D., 1958. The concentration and isotopic abundances of atmospheric carbon dioxide in rural areas. Geochimica et Cosmochimica Acta 13, 322–334. Keller, J.K., Bridgham, S.D., Chapin, C.T., Iversen, C.M., 2005. Limited effects of six years of fertilization on carbon mineralization dynamics in a Minnesota fen. Soil Biology & Biochemistry 37, 1197–1204. Kemmitt, S.J., Wright, D., Goulding, K.W.T., Jones, D.L., 2006. pH regulation of carbon and nitrogen dynamics in two agricultural soils. Soil Biology & Biochemistry 38, 898–911. Kreutzer, K., 1995. Effects of forest liming on soil processes. Plant and Soil 169, 447–470. Kuzyakov, Y., 2006. Sources of CO2 efflux from soil and review of partitioning methods. Soil Biology & Biochemistry 38, 425–448. Lohila, A., Aurela, M., Tuovinen, J.P., Laurila, T., 2004. Annual CO2 exchange of a peat field growing spring barley or perennial forage grass. Journal of Geophysical Research – Atmospheres 109, D18116, doi:10.1029/2004JD004715. Lorenz, K., Preston, C.M., Feger, K.H., 2001. Long-term effects of liming on microbial biomass and activity and soil organic matter quality (C-13 CPMAS NMR) in organic horizons of Norway spruce forests in Southern Germany. Journal of Plant Nutrition and Soil Science 164, 555–560. Maljanen, M., Hyto¨nen, J., Martikainen, P.J., 2001a. Fluxes of N2O, CH4 and CO2 on afforested boreal agricultural soils. Plant and Soil 231, 113–121. Maljanen, M., Martikainen, P.J., Walden, J., Silvola, J., 2001b. CO2 exchange in an organic field growing barley or grass in eastern Finland. Global Change Biology 7, 679–692. Maljanen, M., Komulainen, V.M., Hytonen, J., Martikainen, P., Laine, J., 2004. Carbon dioxide, nitrous oxide and methane dynamics in boreal organic agricultural soils with different soil characteristics. Soil Biology & Biochemistry 36, 1801–1808. Martikainen, P.J., 1996. Microbial processes in boreal forest soils as affected by forest management practices and atmospheric stress. In: Stotzky, G., Bollag, J.M. (Eds.), Soil Biochemistry. Marcell Dekker Inc., New York, pp. 195–232. Midwood, A.J., Gebbing, T., Wendler, R., Sommerkorn, M., Hunt, J.E., Millard, P., 2006. Collection and storage of CO2 for 13C analysis: an application to separate soil CO2 efflux into root- and soil-derived components. Rapid Communications in Mass Spectrometry 20, 3379–3384. Miltner, A., Kopinke, F.D., Kindler, R., Selesi, D.E., Hartmann, A., Kastner, M., 2005. Non-phototrophic CO2 fixation by soil microorganisms. Plant and Soil 269, 193–203. Ministry of the Environment of Finland, 2001. Finland’s Third National Communication under the United Nations Framework Convention on Climate Change. Ministry of the Environment, Helsinki, 197 pp. Murakami, M., Furukawa, Y., Inubushi, K., 2005. Methane production after liming to tropical acid peat soil. Soil Science and Plant Nutrition 51, 697–699.

C. Biasi et al. / Soil Biology & Biochemistry 40 (2008) 2660–2669 Nyka¨nen, H., Alm, J., Lang, K., Silvola, J., Martikainen, P.J., 1995. Emissions of CH4, N2O and CO2 from a virgin fen and a fen drained for grassland in Finland. Journal of Biogeography 22, 351–357. Oh, N.H., Raymond, P.A., 2006. Contribution of agricultural liming to riverine bicarbonate export and CO2 sequestration in the Ohio River basin. Global Biogeochemical Cycles 20, GB3012, doi:10.1029/2005GB002565. Parviainen, T., 2007. Optimization of Reed Canary Grass Cultivation on the Cut-away Peatlands. Ph.D. thesis, Oulu University Press, Oulu, 260 pp. Pataki, D.E., Ehleringer, J.R., Flanagan, L.B., Yakir, D., Bowling, D.R., Still, C.J., Buchmann, N., Kaplan, J.O., Berry, J.A., 2003. The application and interpretation of Keeling plots in terrestrial carbon cycle research. Global Biogeochemical Cycles 17, 1022, doi:10.1029/2001GB001850. Persson, T., Lundkvist, H., Wire´n, A., Hyvo¨nen, R., Wesse´n, B., 1989. Effects of acidification and liming on carbon and nitrogen mineralization and soil organisms in mor humus. Water, Air and Soil Pollution 45, 77–96. Post, W.M., Emanuel, E.R., Zinke, P.J., Strangenberger, A.G., 1982. Soil carbon pools and world life zones. Nature 298, 156–159. Potthoff, M., Loftfield, N., Buegger, F., Wick, B., John, B., Joergensen, R.G., Flessa, H., 2003. The determination of delta C-13 in soil microbial biomass using fumigation-extraction. Soil Biology & Biochemistry 35, 947–954. Robertson, G.P., Paul, E.A., Harwood, R.R., 2000. Greenhouse gases in intensive agriculture: contributions of individual gases to the radiative forcing of the atmosphere. Science 289, 1922–1925. Rosenberg, W., Nierop, K.G.J., Knicker, H., de Jager, P.A., Kreutzer, K., Weiss, T., 2003. Liming effects on the chemical composition of the organic surface layer of a mature Norway spruce stand (Picea abies [L.] Karst.). Soil Biology & Biochemistry 35, 155–165.

2669

Santruckova, H., Bird, M.I., Elhottova, D., Novak, J., Picek, T., Simek, M., Tykva, R., 2005. Heterotrophic fixation of CO2 in soil. Microbial Ecology 49, 218–225. Schlegel, H.G., 1985. Allgemeine Mikrobiologie. Thieme, Stuttgart, 571 pp. Shurpali, N.J., Hyvo¨nen, N.P., Huttunen, J.T., Biasi, C., Nyka¨nen, H., Pekkarinen, N., Martikainen, P.M., 2008. Bare soil and reed canary grass ecosystem respiration in peat extraction sites in eastern Finland. Tellus B 60, 200–209. Stevenson, B.A., Kelly, E.F., McDonald, E.V., Busacca, A.J., 2005. The stable carbon isotope composition of soil organic carbon and pedogenic carbonates along a bioclimatic gradient in the Palouse region, Washington State, USA. Geoderma 124, 37–47. Stevenson, B.A., Verburga, P.S.J., 2006. Effluxed CO2-13C from sterilized and unsterilized treatments of a calcareous soil. Soil Biology & Biochemistry 38, 1727–1733. ¨ ber die Entwicklung der finnischen Moore in Nordkarelien. Tolonen, K., 1967. U Annales Botanici Fennici 4, 219–416. Trumbore, S., 2006. Carbon respired by terrestrial ecosystems – recent progress and challenges. Global Change Biology 12, 141–153. Vance, E.D., Brookes, P.C., Jenkinson, D.S., 1987. An extraction method for measuring soil microbial biomass C. Soil Biology & Biochemistry 19, 703–707. Vasander, H., 1996. Peatlands in Finland. Finnisch Peatland Society, Helsinki, 168 pp. West, T.O., McBride, A.C., 2005. The contribution of agricultural lime to carbon dioxide emissions in the United States: dissolution, transport, and net emissions. Agriculture Ecosystems & Environment 108, 145–154. Wu, J., Joergensen, R.G., Pommerening, B., Chaussod, R., Brookes, P.C., 1990. Measurement of soil microbial biomass C by fumigation-extraction – an automated procedure. Soil Biology & Biochemistry 22, 1167–1169.