June, 2011 Journal of Resources and Ecology Vol.2 No.2

J. Resour. Ecol. 2011 2(2) 168-174 Article DOI:10.3969/j.issn.1674-764x.2011.02.010 www.jorae.cn

Modeling the Effects of and Elevated CO2 on Soil Organic Carbon in an Alpine

LI Xiaojia1,2, ZHANG Xianzhou1* and ZHANG Yangjian1

1 Lasa Station, Key Laboratory of Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China; 2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China

Abstract: The objective of this study was to analyze the effects of climate change and doubled atmospheric

CO2 concentrations, as well as the combined effects of climate change and doubling atmospheric CO2 concentrations on soil organic carbon (SOC) in the alpine steppe of the northern Tibetan Plateau using the CENTURY model. The results indicate that SOC loss in climate change scenarios varied from 49.77– 52.36% in the top 20 cm. The simulation results obtained for a P1T0 scenario (increased and unchanged temperature), P0T1 scenario (unchanged precipitation and increased temperature), and P1T1 scenario (increased precipitation and increased temperature) were similar. The alpine steppe in the P1T1 scenarios lost the greatest amount of SOC (844.40 g C m-2, representing the least amount of SOC) by the end of the simulation. The simulation for P0T1 scenarios resulted in a 49.77% loss of SOC. However,

SOC increased 12.87% under the CO2 doubling scenario, compared with the unchanged CO2 scenario. CO2 enhancement effects on SOC were greater than the climate change effects on SOC alone. The simulation

of combined climate change and doubling atmospheric CO2 led to a decrease in SOC. This result indicated

a decrease of 52.39% in SOC for the P1T1 + 2 × CO2 scenario, 49.81% for the P0T1 + 2 × CO2 scenario,

and 52.30% for the P1T0 + 2 × CO2 scenario over the next 50 years. Therefore, SOC content in the alpine

steppe will change because of changes in precipitation, temperature and atmospheric CO2 concentrations.

Key words: soil organic carbon (SOC); modeling; CENTURY; climate change; CO2 concentration

content is high in (Meersmans et al. 2008) 1 Introduction and assessing the response of SOC to climate change is Climate change is a worldwide concern, and increasing particularly important for such areas.

CO2 concentrations have significant impacts on The effects of temperature increases on carbon storage . The northern hemisphere is an important in grasslands are uncertain. Grasslands are sensitive to terrestrial carbon sink. The implementation of emission climate change (Parton et al. 1994), which impacts soil reduction through rational land use measures could reduce carbon storage. Parton et al. (1995) have estimated global

CO2 emissions from land. Greenhouse gas emissions are productivity and if air temperatures a major driving force of climate change. According to increased by 2–5 ℃, and predicted that SOC in grasslands Intergovernmental Panel on Climate Change (IPCC), if will lose 3–4 Pg C in 50 years, mainly because of unchecked, atmospheric CO2 concentrations may increase the increased SOC decomposition rates due to global from 650 to 970 ppm by 2100 and cause the global warming. Riedo et al. (2000) have indicated that carbon is average temperature to rise by 1.4–5.8 °C between 1990– typically lost from grazed grassland with a 4 ℃ increase in 2100 (Houghton et al. 2001). Soil is the main source of temperature and increased precipitation; moreover, carbon atmospheric CO2, and the biggest carbon pool in terrestrial storage increases with a 2 ℃ increase in temperature. ecosystems (Schlesinger 1990). Soil organic carbon (SOC) Thornley et al. (1997) and Cao et al. (1998) have predicted

Received: 2011-03-07 Accepted: 2011-04-27 Foundation: the National Key Research Program (2010CB951704). *Correspending author: ZHANG Xianzhou. Email: [email protected]. LI Xiaojia, et al.: Modeling the Effects of Climate Change and Elevated CO2 on Soil Organic Carbon in an Alpine Steppe 169 that temperate grasslands would become a carbon sink 2 Materials and Methods with increasing temperature. In addition, alpine terrestrial 2.1 Study area ecosystems are extremely sensitive to global climate The site of Bange (31.39 °N, 90.31 °E) was selected as change (Luo et al. 2002; Zhang et al. 2007). Therefore, a representative site of alpine on the northern grasslands on the northern Tibetan Plateau, which are Tibetan Plateau. Mean elevation is 4630 m. The land is sensitive to climate change, have been selected to study cold and dry and has a continental highland climate typical the possible effect of climate change on SOC. The impacts of a semi-arid region. Mean annual precipitation is 325.25 of climate change on SOC were found to be negative mm, and mean annual air temperature is –0.67 ℃ (range: or positive in the alpine steppe on the northern Tibetan –27.26–19.68 ℃). mainly consists of Stipa Plateau. purpurea, Carex moorcroftii, and Leontopodium stracheyi Recently, many studies have successfully used the (Table 1). The soil type is cold frozen calcium (alpine CENTURY model (Gilmanov et al. 1997), which is an steppe soil). ecosystem level model used to evaluate the possible impact of climatic change on grassland ecosystems (Ojima 2.2 Methods et al. 1993; Riedo et al. 1997). The model has wide Field surveys and sampling were conducted in 2009. Soil applications in grasslands (Xiao et al. 1996), having been samples were collected from the top 20 cm of the soil to used originally in the Great Plains Grasslands (Parton et test SOC using the potassium dichromate method. Specific al. 1987). It divides soil organic matter pools into active, climate and soil characteristics including soil texture, pH, slow and passive organic matter pools (Parton et al. 1992). and the soil bulk density in Bange, were used as initial However, few studies have been done on SOC storage conditions to initiate the CENTURY model (Tables 2 and dynamic changes in an alpine steppe, especially in the and 3). Climate data such as daily precipitation, daily northern Tibetan Plateau. maximum temperature, daily minimum temperature, and Our objective was to model the dynamics of SOC and daily mean temperature data from 1980 to 2009 were evaluate the potential SOC response to climate change obtained from the China Meteorological Data Sharing and atmospheric CO changes in the alpine grasslands 2 Service System and used to create a factual weather file. of the northern Tibetan Plateau for the next 50 years. The alpine steppe is generally used as the main grazing These findings may serve as basis for studying the effect region on Tibetan Plateau, and the main human activity in of climate change on the density of SOC on the Tibetan this region is grazing. Plateau and provide a scientific reference for grassland A grazing factor was added to fixed management management. scenarios in the model. The steppes are grazed from

Table 1 Vegetation survey of the Bange alpine steppe.

Alpine steppe Height Coverage Biomass No. Species (cm) (%) (g m-2) Dominance 1 Gentiana crenulato–truncata (Marq.) T.N.Ho 0.3 0.10 0.023 0.040 2 Artemisia duthreuil–de-rhinsi Krasch. 1.2 0.17 0.042 0.098 3 Oxytropis stracheyana Benth.ex Baker 0.7 1.20 0.547 0.113 4 Youngia simulatrix (Babc.) Babc.et Setbb. 1.2 0.17 0.046 0.119 5 Anemone obtusiloba D.Don.ssp.ovalifolia Bnühl. 1.1 1.05 0.354 0.145 6 Viola philippica Sasaki 1.2 1.20 0.043 0.146 7 Meconopsis horridula Hook.f.et Thoms. 2.0 0.30 0.057 0.194 8 Rhodiola quadrifida (Pall.) Fisch.et Mey. 2.0 0.25 0.084 0.210 9 Taraxacum cf.parvulum (Wall.) DC. 2.3 4.90 1.365 0.261 10 Astragalus polycladus Bur.et Franch. 3.0 0.73 0.147 0.269 11 Carex moocroftii Falc.ex Boott 3.5 1.80 0.540 0.276 12 Delphinium caeruleum Jacquem.ex.Cambess. 5.0 0.80 0.499 0.369 13 Leontopodium stracheyi (Hook.f.) 2.0 5.98 2.826 0.388 C.B.Clark.ex Hamsl.Var.tenuicaule Beauv. 14 Poa boreali-tibetica C.Ling 4.6 1.00 0.166 0.437 15 Festuca ovina Linn. 4.9 1.74 0.904 0.506 16 Carex ivanovae Egorova 6.6 0.98 0.630 0.604 17 Stipa purpurea Griseb. 6.0 2.90 0.847 0.610 170 Journal of Resources and Ecology Vol.2 No.2, 2011 Table 2 Climate parameters in Bange from 1980 to 2009. to 2004 (Yang et al. 2008) were used. The SOC simulation Temperatures (℃) Precipitation (cm) in Bange by the CENTURY model showed good results. The Pearson correlation coefficient between the simulated Month Minimum Maximum Mean s.d. Skewness values and observed data was 0.651. Finally, changes in 1 –25.867 2.990 0.217 0.234 1.641 SOC pools for the next 50 years were simulated under 2 –23.610 3.777 0.224 0.217 1.347 different climate change scenarios. 3 –19.003 7.273 0.289 0.221 1.067 4 –13.477 10.297 0.624 0.428 0.774 Alpine steppe is widely distributed in the northern 5 –8.010 15.013 2.222 1.843 0.498 Tibetan Plateau and is climatically sensitive. In this 6 –2.887 18.987 5.872 2.846 0.407 study, different climate change scenarios were selected to 7 0.263 18.637 8.353 3.317 0.567 determine the potential effects of future climate change 8 –0.340 17.847 8.678 3.486 0.620 on SOC in the alpine steppe; these were then compared 9 –3.913 15.953 5.623 2.596 0.781 with an unchanged climate scenario. The changes in SOC 10 –12.087 12.673 1.117 1.021 0.723 were simulated in conjunction with possible changes in 11 –19.250 5.527 0.245 0.371 2.445 precipitation, temperature and doubling atmospheric CO2 12 –24.227 4.033 0.180 0.149 0.371 concentrations. These are important influencing factors Variable tmn2m tmx2m precip prcstd prcskw on SOC. Both single factor effects and combined effects on SOC were considered in order to determine the effect Notes: Variable PRECIP, PRCSTD, PRCSKW, TMN2M, and TMX2M represent the average monthly precipitation (cm), standard deviation of climate change on SOC in detail. The climate change of monthly precipitation, skewness of monthly precipitation, average scenarios were determined by increasing the temperature month minimum air temperatures (℃), and average month maximum air by 2 ℃ and precipitation by 5 mm monthly to simulate temperatures (℃), respectively. the effect of climate change on SOC for the next 50 years. Table 3 Site position and soil parameters of the top 20 cm in In addition, 2 ℃ warming scenarios were set on the Bange. average distribution of 2 ℃ for 50 years on the basis of meteorological data in unchanged climate, i.e., a monthly PROPERTY VALUE VARIABLE increase of 0.04 ℃. Brief descriptions of the four future Latitude(degree) 31.390 SITLAT scenarios are provided in Table 4. Longitude(degree) 90.310 SITLNG Data were calculated as means with standard error SAND (fraction 0–1) 0.668 SAND using SPSS 13 (SPSS Inc., Chicago, USA). Pearson SILT (fraction 0–1) 0.063 SILT correlation coefficients between climate scenarios were CLAY (fraction 0–1) 0.065 CLAY also calculated. ROCK (fraction 0–1) 0.205 ROCK BULK DENSITY (g cm-3) 1.676 BULKD 3 Results and Discussions pH 6.713 pH 3.1 Effects of climate change alone on SOC density According to our calculations, soil organic density in the October to April of the next year and used as ungrazed topsoil (0–20 cm) can decrease from 1772.30 g m-2 to land from May to September. The same land management 846.04, 890.21, and 844.40 g m-2 in the P1T0, P0T1, and practices were used in all simulations. Factual land P1T1 scenarios respectively, without elevated CO2 in the management practice, mainly grazing, was used to set next 50 years. The effects of SOC on climate change in the the schedule file. First, the CENTURY model was run alpine steppe show a similar trend to grasslands in Inner 5000 years to equilibrium using random climate based Mongolia (Xiao et al. 1996). on current climate conditions. The equilibrium was then There was a great amount of variation in SOC under used as the initial conditions for running the model, using climate scenarios. The content of SOC increased slightly, meteorological data from 1980 to 2009. To validate the by 0.14% in the unchanged climate scenarios for the model, factual sampling data from 2009, China’s second next 50 years. The effects of climate change on SOC in state soil survey data from 1985 to 1990 (Regional the alpine steppe were consistent in reducing the content Planning Office of Naqu 1991), and field data from 2001 of soil carbon in the climate change scenarios for the

Table 4 Explanation of the scenarios considered in our modelling.

Scenarios Description Period P0T0 Precipitation and temperature are unchanged 2010–2059 P1T0 Precipitation increase by 5 mm/month; temperature unchanged 2010–2059 P0T1 Precipitation unchanged; temperature increase by 2 °C 2010–2059 P1T1 Precipitation increase by 5 mm/month; temperature increase 2 °C 2010–2059 LI Xiaojia, et al.: Modeling the Effects of Climate Change and Elevated CO2 on Soil Organic Carbon in an Alpine Steppe 171

Table 5 Variation of SOC pools in the next 50 years in an alpine grassland.

Start value in End value in Variation during SOC simulation simulation simulation (mean ± S.E.) -2 -2 Scenarios Carbon pool (g m ) (g m-2) (%) (g m )

P0T0 Active SOC 49.99 51.90 +3.83 51.02 ± 0.28 Slow SOC 1210.04 1210.69 +0.05 1209.95 ± 0.58 Passive SOC 512.26 512.17 0.02 512.22 ± 0.01 SOC 1772.30 1774.77 +0.14 1773.18 ± 0.63 P1T0 Active SOC 49.99 5.97 –88.05 16.33 ± 1.61 Slow SOC 1210.04 339.14 –71.97 736.43 ± 40.48 Passive SOC 512.26 500.92 –2.21 507.66 ± 0.51 SOC 1772.30 846.04 –52.26 1260.42 ± 42.42 P0T1 Active SOC 49.99 6.69 –86.61 17.20 ± 1.63 Slow SOC 1210.04 381.32 –68.49 769.87 ± 38.71 Passive SOC 512.26 502.20 –1.96 508.20 ± 0.46 SOC 1772.30 890.21 –49.77 1295.27 ± 40.62 P1T1 Active SOC 49.99 5.95 –88.11 16.30 ± 1.61 Slow SOC 1210.04 337.58 –72.10 735.19 ± 40.55 Passive SOC 512.26 500.87 –2.22 507.64 ± 0.51 SOC 1772.30 844.40 –52.36 1259.12 ± 42.50

Notes: SOC = active SOC + slow SOC + passive SOC; + increase; – decrease. next 50 years. The responses of SOC to the changes in the P1T1 scenario was not significantly different from temperature and precipitation were also similar. The those in the P1T0 and P0T1 scenarios. The interaction of impact of climate change on SOC had little difference in combined increasing temperature and precipitation may the P1T1, P1T0 and P0T1 scenarios. SOC decreased by offset the impact on ecosystem processes. 52.36% in the P1T1 scenario, and this was the maximum Active SOC is composed of microbes and their variation. SOC declined by 52.26% in the P1T0 scenario metabolites. Variation in active SOC was large in climate and declined by 49.77% in the P0T1 scenario (Table 5). change scenarios, although they decreased by 88% due to Climate change alone caused SOC to decrease. The results a quick turnover rate and the high sensitivity of the area to are in agreement with Parton et al. (1995), whose study climate change. Slow SOC reduced by approximately 70% simulated SOC in seven grassland regions (cold desert and was a major contributor because of more contents steppe, temperate steppe, humid temperate, Mediterranean, and variation. The variation of passive SOC was small, dry savanna, savanna, and humid savanna), but did not decreasing by about 2% due to a low sensitivity to climate include the alpine region. change (Fig. 1). The mean and standard errors of SOC were similar under the climate change scenarios. SOC in the unchanged 3.2 Impact of increased atmospheric CO2 climate (P0T0) scenario had no significant correlation with concentrations alone on soil carbon that in the other climate change scenarios (P1T0, P0T1, Increasing atmospheric CO2 concentrations can increase and P1T1). However, SOC in the P1T0, P0T1 and P1T1 the photosynthetic rate of plants, water use efficiency and scenarios were correlated (p < 0.001). nutrient use efficiency (Owensby et al. 1993). In addition, Climate warming has accelerated respiration, resulting this can lead to increased plant productivity, plant litter and in the reduction of carbon storage, especially soil carbon plant roots, and SOC. As a result of the CO2 fertilization storage (Houghton and Woodwell 1989, Oechel et al. effect terrestrial C stock can increase by 0.5–4.0 Gt C each 1993, Schimel et al. 1994). Humidity and temperature year (Gifford 1994). changes affect the decomposition rate of soil organic After simulating the effects of doubling atmospheric matter (Alm et al. 1999, Parton et al. 1987, Schimel CO2 on soil C at the Bange alpine steppe for the next et al. 1994). Generally, an increase in temperature and 50 years, the results showed that the content of SOC precipitation increases the primary productivity of fractions in doubling atmospheric CO2 concentrations vegetation. The content of SOC changes as temperature alone produced a C sink. It was significantly higher than increases, enhancing soil respiration and accelerating the that under the unchanged atmospheric CO2 concentration decomposition of organic matter while also increasing scenario (Fig. 2). The simulation results obtained for evaporation. SOC density is usually low in hot and dry doubling CO2 concentration were similar to those by environments (Xie et al. 2004). The impact on SOC under other studies regarding tropical savannas, humid savanna 172 Journal of Resources and Ecology Vol.2 No.2, 2011 ) ) ) -2 -2 ) -2 -2 Slow SOC (g m Active SOC (g m Slow SOC (g m Active SOC (g m

Simlation time (year) Simlation time (year) Simlation time (year) Simlation time (year) ) -2 ) -2 ) ) -2 -2 SOC (g m SOC (g m Passive SOC (g m Passive SOC (g m

Simlation time (year) Simlation time (year) Simlation time (year) Simlation time (year)

Fig. 1 Comparison of soil carbon accumulation under different Fig. 2 The effect of atmospheric CO2 concentration changes climate scenarios in the next 50 years in an alpine steppe. on SOC in an alpine steppe for the next 50 years. regions and temperate grasslands (Ni 2001; Parton et al. 1995; Thornley et al. 1997). Compared with soil carbon ) fractions in unchanged CO2, the variations in doubling -2

CO2 concentrations showed a similar trend and all increased by more than 10% (Table 6). Particularly, active doubling CO2 SOC increased by 15.84% on average with the doubling y=497.75+0.74x (R2=0.90) unchangable CO of atmospheric CO2 concentrations for the next 50 years, 2 increased by 13.14% for slow SOC, and increased by y=1841.73–0.03x (R2=0.01)

11.93% for passive SOC. Compared with SOC content carbon (g m Soil organic under unchanged CO2 concentrations, that under the doubling of an atmospheric CO2 concentration evidently increased for the next 50 years, fitted by a linear equation (Fig. 3). Simlation time (year) 3.3 Combined effect of climate change and doubling

atmospheric CO2 Fig. 3 Linear fit of soil carbon in unchanged CO2

The fractions of SOC increased under a doubling of CO2 concentration and doubling CO2 concentrations. concentration alone. However, each fraction of SOC pool proved to be significantly lower in the scenarios in which a substantial increase of SOC in terrestrial of combined climate change and doubling CO2. The ecosystems on a global scale was observed. The combined variations of SOC in these scenarios were close. The effect effects of doubling atmospheric CO2 and climate change of climate change on SOC offsets the CO2 fertilization on SOC in this alpine steppe ecosystem on the northern effect. SOC content decreased by 52.30% in P1T0 + 2 Tibetan Plateau followed an opposite trend to that of the

× CO2 , by 49.81% in P0T1 + 2 × CO2, and by 52.39% global trend, indicating the uniqueness alpine ecosystems. in P1T1 + 2 × CO2 over the next 50 years (Table 7). Our The SOC response to increased CO2 and temperature results differ from the results of Cao and Woodward (1998), in the alpine steppe, which produced a carbon source,

Table 6 Changes in soil carbon components in an alpine steppe for the next 50 years (mean ± S.E.).

Active SOC Slow SOC Passive SOC SOC Change scenarios (g m-2) (g m-2) (g m-2) (g m-2)

Unchanged CO2 51.02 ± 0.28 1209.95 ± 0.58 512.22 ± 0.01 1773.18 ± 0.63

Doubling CO2 59.10 ± 0.28 1368.92 ± 1.47 573.33 ± 0.01 2001.36 ± 1.60 Variation (%) +15.84 +13.14 +11.93 +12.87

Notes: SOC = active SOC + slow SOC + passive SOC; + increase; – decrease. LI Xiaojia, et al.: Modeling the Effects of Climate Change and Elevated CO2 on Soil Organic Carbon in an Alpine Steppe 173

Table 7 Combined effects of climate change and doubling atmospheric CO2 on SOC pools in an alpine grassland for the next 50 years.

Start value in End value in Variation during SOC simulation simulation simulation (mean ± S.E.) -2 -2 Scenarios Carbon pool (g m ) (g m-2) (%) (g m )

P0T0 + Active SOC 56.28 61.44 +9.18 59.10 ± 0.28

2 × CO2 Slow SOC 1354.00 1386.86 +2.43 1368.92 ± 1.47 Passive SOC 573.24 573.51 +0.05 573.33 ± 0.01 SOC 1983.51 2021.81 +1.93 2001.36 ± 1.60 P1T0 + Active SOC 56.28 6.67 –88.14 18.28 ± 1.81

2 × CO2 Slow SOC 1354.00 379.00 –72.01 823.55 ± 45.33 Passive SOC 573.24 560.53 –2.22 568.08 ± 0.57 SOC 1983.51 946.21 –52.30 1409.91 ± 47.52 P0T1 + Active SOC 56.28 7.48 –86.71 19.25 ± 1.82

2 × CO2 Slow SOC 1354.00 426.17 –68.53 860.94 ± 43.35 Passive SOC 573.24 561.97 –1.96 568.69 ± 0.51 SOC 1983.51 995.62 –49.81 1448.88 ± 45.49 P1T1 + Active SOC 56.28 6.64 –88.19 18.24 ± 1.81

2 × CO2 Slow SOC 1354.00 377.25 –72.14 822.15 ± 45.42 Passive SOC 573.24 560.48 –2.23 568.06 ± 0.58 SOC 1983.51 944.38 –52.39 1408.45 ± 47.61

Notes: SOC = active SOC + slow SOC + passive SOC; + increase; – decrease.

were inconsistent with research done in different regions. in the combined climate change and doubling CO2 For example, humid and temperate grasslands are likely concentrations. SOC declined by 52.36% in response to to be a carbon sink (Thornley et al. 1997). Therefore, the climate change under the P1T1 scenario, increased by combined effects of climate change and doubling CO2 on 1.93% in response to doubled CO2 alone, and declined SOC in alpine ecosystems are different to those in other by 52.39% in response to the combination of P1T1 and regions and the responses of SOC to climate change in doubled CO2, as compared with an increase of 0.14% in no alpine regions requires further research. climate change. Compared with variations on SOC pools in climate change alone scenarios, the results for the combined Acknowledgments The authors are grateful to Cindy Keough from the Natural climate change and doubling atmospheric CO2 scenarios Resources Ecology Lab-Colorado State University for running the were a little larger. Doubled CO2 may have caused evapotranspiration to decrease, and water use efficiency CENTURY model. Suggestions and field assistance were provided to increase, partially offset by climate change (Riedo et by WU Jianshuang, WU Junxi and LU Wenjie. al. 1997). The combined effects of climate change and References doubling atmospheric CO2 on SOC were maximal and Alm J, L Schulman, J Walden, H nen Nyk, P Martikainen, et al. 1999. Carbon formed a positive feedback on atmospheric CO2. The effects of doubling CO alone on SOC were relatively balance of a boreal bog during a year with an exceptionally dry summer. 2 Ecology, 80 (1): 161–174. small, although it increased the content of SOC. Cao M and F Woodward. 1998. Dynamic responses of terrestrial ecosystem carbon cycling to global climate change. Nature, 393 (1): 249–252. 4 Conclusions Gifford R. 1994. The global carbon cycle: a viewpoint on the missing sink. Australian Journal of Plant Physiology ,21 (1): 1–15. SOC dynamics for the next 50 years were successfully Gilmanov T G, W J Parton and D S Ojima. 1997. Testing the ‘CENTURY’ simulated using the CENTURY model. The impact of ecosystem level model on data sets from eight grassland sites in the former USSR representing a wide climatic/soil gradient. Ecological Modelling, different climate change scenarios and doubling CO2 96:191–210. concentrations on SOC in an alpine steppe were analyzed, Houghton J, Ding Y, D Griggs, M Noguer, P Van der Linden, et al. 2001. the results of which vary. The SOC pool showed a slight IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of increasing trend under the P0T0 scenario (no climate Working Group I to the Third Assessment Report of the Intergovernmental change during the simulation). Thus, negative impacts Panel on Climate Change, 9. Houghton R and G Woodwell. 1989. Global climatic change. Scientific of climate alone on SOC in alpine steppes were found. American, 260 (4): 36–44. SOC pools decreased significantly under various climate Luo T, Li W and Zhu H. 2002. Estimated biomass and productivity of natural change scenarios. SOC density significantly increased in vegetation on the Tibetan Plateau. Ecological Applications, 12 (4): 980– 997. the doubled CO2 concentration alone and also decreased Meersmans J, F De Ridder, F Canters, S De Baets and M Van Molle. 2008. 174 Journal of Resources and Ecology Vol.2 No.2, 2011

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模拟气候变化和CO2增加对高寒草原土壤有机碳的影响

李晓佳1,2，张宪洲1，张扬建1

1 中国科学院地理科学与资源研究所生态系统网络观测与模拟重点实验室拉萨高原生态试验站，北京 100101； 2 中国科学院研究生院，北京 100049

摘要: 本研究的目标是利用CENTURY模型分析气候变化、大气CO2浓度倍增、气候变化与大气CO2浓度倍增共同作用对藏 北高原高寒草原土壤有机碳的影响。结果表明：未来50年不同气候变化情景下土壤表层（0–20cm）有机碳呈降低趋势，变化率为 49.77%–52.36%。P1T0情景（降水增加，温度不变）、P0T1情景（降水不变，温度增加）和P1T1情景（降水增加，温度增加）下 的模拟结果相近。其中P1T1情景下高寒草原土壤有机碳损失的最多（模拟结束时的土壤有机碳为844.40 g C m-2），P0T1情景下土

壤有机碳损失49.77%。相对CO2不变情景而言，CO2倍增情景下土壤有机碳增加12.87%。CO2增加对土壤有机碳的影响大于气候变

化单独作用对土壤有机碳的影响。气候变化与大气CO2浓度倍增共同作用导致土壤有机碳降低。未来50年P1T1 + 2 × CO2情景下

土壤有机碳降低52.39%，P0T1 + 2 × CO2情景下土壤有机碳降低49.81%，P1T0 + 2 × CO2情景下土壤有机碳降低52.30%。因此，

高寒草原土壤有机碳含量随降水、温度和大气CO2浓度的变化而变化。

关键词：土壤有机碳；模拟；CENTURY；气候变化；CO2浓度