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

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Modeling the Effects of Climate Change and Elevated CO2 on Soil Organic Carbon in an Alpine Steppe 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 Climate Change and Elevated CO2 on Soil Organic Carbon in an Alpine Steppe LI Xiaojia1,2, ZHANG Xianzhou1* and ZHANG Yangjian1 1 Lasa Station, Key Laboratory of Ecosystem 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 precipitation 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 grasslands (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 ecosystems. 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 grassland productivity and soil carbon 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 steppes 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 ℃). Vegetation 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.
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