What Should we do in the Context of Land Use Change Occurring Frequently in China?
Received: 09-Feb-2018 / Accepted Date: 01-Mar-2018 / Published Date: 06-Mar-2018 DOI: 10.4172/2157-7617.1000454
China’s effort to mitigate soil organic carbon (SOC) loss caused by rapid land use changes over the last two decades faces great challenges. Generally, land use change projects in China have been performed without considering the mechanisms involved in the link between land use change and SOC dynamic. Such situation will likely increase the climatic and environmental risks brought by land use changes. In this paper, we illustrate why most studies over the past several decades in China have been unable to provide significant guiding information for what kind of land use can be adopted to benefit the climate and ecological environments. In addition, we recommend the combination of soil organic matter fractionation with radiocarbon assessment, which researchers are working on to better predict the dynamic trends of SOC under land use change and present several proposals in regard to how to sequester more carbon in soils after land use change.
Keywords: Land use change; Radiocarbons; Fractionation of soil organic matter; Soil carbon sequestration
Land use change and SOC dynamics
Globally, soils store more than twice the amounts of carbon present in atmospheric CO2. SOC stock is determined by the balance of net carbon inputs to the soil (e.g. organic matter) and net carbon losses from the soil (e.g. CO2, dissolved organic carbon, and the loss through erosion). Land use change is identified as the main driving for the balance between carbon inputs and losses in soil [1,2]. Therefore, changes in land use and land management are important causes of SOC store variation; such variation could lead to a marked climate change because altering in climate patterns is associated with atmospheric CO2 concentration . Approximately 545 Gt of carbon have been released in the atmosphere by land use change and the use of fossil fuels, which resulted in an increase in the atmospheric CO2 concentration from the range of 275 ppm to 281 ppm in 1750 to 390 ppm in 2011 and 400 ppm in 2013 .
Significant changes of land use have occurred in China over the last two decades . The cropland area decreased in the south and increased in the north; however, the total area remained almost unchanged. The reclaimed cropland was shifted from the northeast to the northwest. The built-up lands expanded rapidly and were mainly distributed in the east. Moreover, these lands gradually spread out to Central and Western China. Woodland decreased initially and increased eventually; however, desert area showed the opposite result. Grassland continued to decrease. These changes have greatly affected the ecosystem carbon processes, particularly the exchanges of carbon between the atmosphere and terrestrial carbon pools; they have also affected vegetation cover, photosynthesis, biodiversity, nitrogen utilization, and soil organic matter composition [6,7], all of which are associated with global carbon cycling, which consequently affects climate change. Inappropriate land use and management in China have exacerbated approximately 8 Gt to 14 Gt of carbon depletion in soils, and 50% to 60% of these carbon emissions can be restored by restoring degraded soil and ecosystem [8,9]. Thus, understanding how land use and management affect SOC sequestration for sustainable development of China while improving soil and ecosystem resilience is an urgent demand.
Barriers to the implementation of land use change in China in view of SOC dynamic mechanisms
Land use changes over the recent decades in China were primarily driven by national land policy and development programs, economic growth, and agricultural expansion. Such situation will likely increase the climatic and environmental risks from land use change, which will ultimately affect the climate and environment adversely. In China, a close relationship between land use and SOC dynamics have been reported in several studies [6,10-15], which may be able to provide some significant guiding information for what kind of land use would be beneficial for climate and ecological environments. However, in order to better implement land use change in view of SOC dynamic mechanisms, a process-based understanding in relation to the mechanisms involved in the link between land use change and SOC dynamic may be still needed, and several issues must be taken into account as follows: (1) Most previous studies only focused on the SOC content and storage change under land use change. In addition, they only emphasized on the short-term processes that dominate carbon balance at the point or soil profile scale; whereas other processes that dominate over longer timescales and larger spatial scales may actually be more important in determining the carbon balance of soils under land use change . (2) Soil organic matter comprises a vast range of different functional pools with a turnover time in soil that ranges from less than one year to thousands of years. However, soil organic matter in most previous studies was treated as a homogeneous pool with a single turnover time; this condition may overestimate SOC response on long-term scales . (3) The most common approaches used to evaluate the dynamics of SOC in previous studies include the first-order kinetic equation fitting method , natural abundance 13C labeling tracer method , and soil respiration measurement method . Although these approaches have provided a number of important insights into SOC dynamics, they cannot be used in all ecosystems and cannot be reliably applied to study SOC dynamics on extremely long timescales.
Discussion And Recommendations
Application of the underutilized radiocarbon tool in China must be developed
To cope with the problem of high environmental risks caused by land use change and to provide highly valuable information to predicate the feasibility of land use change, systematic identification of the mechanisms involved in SOC dynamics at long-term scales under land use change in China should be addressed immediately. Natural abundance radiocarbon analysis is one of the methods used to study SOC dynamics on decadal to millennial timescales; in addition, this approach provides a means to directly test the SOC dynamics models under land use change . The combination of soil organic matter fractionation with radiocarbon assessment is a useful means to study the age of organic matter that is associated with specific mineral phases or soil structural components . Such combination can also help to reconstruct the pathways and timescales of soil organic matter transformation under land use change. Therefore, future studies in China should focus on this approach.
However, the adoption of radiocarbon analysis based on soil organic matter fractions in China is challenging because of several reasons. (1) The major challenge is not to failure to identify a single, universal method to separate organic matter into pools that cycle with different intrinsic timescales in all soil types, but the goal to understand what information can be obtained from each method for the scientific questions, because the numerous methods that are available for SOC fractionation [22-25] can only provide limited success, e.g. low-density or large-size fractions of soil organic matter can contain a component of distinct chemical properties and dynamics; in addition, the oldest chemically isolated fractions may also contain material with younger organic matter. (2) Prior to 2000, most radiocarbon measurements in China were made by decay counting, which has been abandoned gradually because it requires several grams of carbon and days or weeks of counting to observe enough decay events for a precise analysis of radiocarbon content. Since 2000s, accelerator mass spectrometry (AMS) has been employed to measure radiocarbon in China because this technique requires only a fairly small sample that is 10,000–100,000 times less than that of decay counting and only requires minutes for one sample. However, only three laboratories in China have AMS machines because of inadequate funding for scientific research, which is not the case in many developed countries. In addition, only a small number of researchers are focusing on the natural abundance radiocarbon analysis. Moreover, most samples for radiocarbon measurements in these laboratories are associated with archaeology, paleontology, history, and geochemistry . Such situation results in the inability to meet the demand for a considerable number of soil samples for the study of SOC dynamic because the number does not correspond to the extremely large land area and the various land use change in China. Hence, to meet the increasing demand for radiocarbon analyses of soil samples, China has to install more AMS machines or strengthen international cooperation with other countries with more AMS laboratories for radiocarbon measurements. (3) Currently, an increase in the demand to process small-mass samples for AMS radiocarbon measurements has been reported, especially when radiocarbon concentration of operationally isolated fractions or biomarkers of soil with very low carbon content is measured. Although several radiocarbon AMS laboratories worldwide have been working on reduction of the required sample size down to a few micrograms carbon [27-30], the ongoing goal in AMS toward small sample size in China presents challenges in both AMS data acquisition and the methods of small-mass graphite preparation. In fact, several radiocarbon AMS laboratories around the world have been working on reduction of the required sample size down to a few micrograms carbon. However, all radiocarbon AMS laboratories in China may require more than 0.5 mg carbon for a precise estimate of radiocarbon concentration, so both hardware improvements of radiocarbon AMS machines and the development of a dedicated graphitization system should be undertaken to produce a high-quality target that guarantees an accurate radiocarbon analysis for small amount of sample material, and thus to reduce sample size to significantly below 0.1 mg carbon.
Effective measures to sequester SOC after land use change must be adopted
Forecast of the SOC dynamics before the implementation of a land use change project is necessary; however, this approach does not suggest that the Chinese government does not work on the soils or lands, whose use patterns have been changed. According to nationwide multiple-target regional geochemical survey, the SOC density in China averages 48.8 t C/ha, which is lower than 50.3 t C/ha of the United States and 70.8 t C/ha of European Union. This finding indicates great potential of soil carbon sequestration in China. Hence, to encourage and support the development of efficient ways to increase carbon sequestration in soil is a no-time-to-delay task for the Chinese government. In Northern China, especially in northeast area, where most crops straw is not returned to soil as carbon inputs, the storage of organic carbon in cultivated soil is 50% lower than that of primitive soil without cultivation. Therefore, the amount of organic carbon in farmland soils can be significantly increased by mere adaptation of the measure of returning crops straw to soil. Given that the storage of soil organic matter in China can be increased by 30% to 40% within 30 years, the increased organic carbon sequestered in cultivated soil will still reach one billion tons. This value equals the sum of those in the United States and Canada. If cultivated land is combined with barren land and pasture land, a greater potential of the soil sequestering organic carbon is expected to mitigate atmospheric CO2 in China than that in Northern America. Interestingly, in most dryland agriculture and forestry areas in China, rainfall may limit the amount of organic carbon that can be added into the soil. However, sometimes, plant nutrition sets the limit.
It has been suggested to sequester organic carbon in soils using relatively inefficient and more resistant material such as biochar and fly ash . In China, substantial works on biochar and fly ash are currently available [32-37], which will certainly provide significant guiding information for farmers to sequester carbon in soils by using biochar and fly ash as soil ameliorant or fertilize. According to an estimation of Woolf , if all of the crop residues in the world were converted into biochar, approximately 1 Gt of carbon would be sequestered. Biochar technology can be estimated to store approximately 2.2 Gt of carbon annually worldwide by 2050. The potential of biochar to sequester carbon in soils may vary depending on biochar characteristics, inherent soil properties, and climate conditions [39,40]. These factors must be taken into account when using biochar.
In addition, increasing the amount of attainable SOC stored below a depth of 1m is a good strategy. At this depth, SOC may be kept for long in stable forms, by selecting plant species that can provide a greater amount of roots in the subsoil to increase the amount of SOC that may dissolve and move down .
Although several approaches have been proposed to increase SOC stocks, the energy and carbon costs associated with achieving attainable organic soil carbon levels must be counted in any carbon budget. The net benefits of carbon sequestration in soils may not be as large as first expected and some processes that increase carbon sequestration may have adverse environmental effects, particularly on biodiversity and ecosystems. In fact, decisions on how to manage SOC in China remain uncertain. Therefore, more effort is needed to detect long-term dynamic of SOC under land use change in China.
The authors thank Ke Sun of Beijing Normal University and Da An of Chinese Research Academy of Environmental Sciences for constructive discussions. This work was supported financially by the National Natural Science Foundation of China (Project Nos. 41501242) and the Major Science and Technology Program for Water Pollution Control and Treatment (No. 2012ZX07203-003) of China.
- Smith P (2008) Land use change and soil organic carbon dynamics. Nutr Cycl Agroecosyst 81: 169–178
- Fiedler SR, Buczk U, Jurasinski G, Glatzel S (2015) Soil respiration after tillage under different fertiliser treatments – implications for modelling and balancing. Soil Tillage Res 150: 30–42
- Lal R (2004) Soil carbon sequestration impacts on global climate change and food security. Science 304: 1623−1627
- IPCC (2013) Climate Change 2013: The physical science basis. Intergovernmental Panel on Climate Change. Working Group I Contribution to the IPCC Fifth Assessment Report (AR5). Cambridge University Press, New York, USA.
- Liu J, Kuang W, Zhang Z, Xu X, Qin Y, et al. (2014) Spatio-temporal characteristics, patterns, and causes of land-use changes in China since the late 1980s. J Geogr Sci 24: 195−210
- Gong J, Wang Y, Liu M, Huang Y, Yan X, et al. (2014) Effects of land use on soil respiration in the temperate steppe of Inner Mongolia, China. Soil Tillage Res 144: 20–31
- Purton K, Pennock D, Leinweber P, Walley F (2015) Will changes in climate and land use affect soil organic matter composition? Evidence from an ecotonal climosequence. Geoderma 253–254: 48–60
- Lal R (2004) Offsetting China’s CO2 emissions by soil carbon sequestration. Climatic Change 65: 263–275
- Zhao X, Zhang R, Xue J, Pu C, Zhang X, et al. (2015) Management-induced changes to soil organic carbon in China: A meta-analysis. Advances in Agronomy 134:1-50
- Gao J, Pan G, Jiang X, Pan J, Zhuang D (2008) Land-use induced changes in topsoil organic carbon stock of paddy fields using MODIS and TM/ETM analysis: A case study of Wujiang County, China. J Environ Sci 20: 852–858
- Liu X, Li F, Liu D, Sun G (2010) Soil organic carbon, carbon fractions and nutrients as affected by land use in semi-arid region of Loess Plateau of China. Pedosphere 20: 146–152
- Wang S, Wang X, Ouyang Z (2012) Effects of land use, climate, topography and soil properties on regional soil organic carbon and total nitrogen in the Upstream Watershed of Miyun Reservoir, North China. J Environ Sci 24: 387–395
- Tao Y, Li F, Wang R, Zhao D (2014) Effects of land use and cover change on terrestrial carbon stocks in urbanized areas: a study from Changzhou, China. J Clean Prod 103: 651–657
- Ouyang W, Lai X, Li X, Liu H, Lin C, et al. (2015) Soil respiration and carbon loss relationship with temperature and land use conversion in freeze – Thaw agricultural area. Sci Total Environ 533: 215–222
- Sun W, Zhu H, Guo S (2015) Soil organic carbon as a function of land use and topography on the Loess Plateau of China. Ecol Eng 83: 249–257
- Trumbore S (2009) Radiocarbon and soil carbon dynamics. Annu Rev Earth Planet Sci 37: 47−66
- Knorr W, Prentice IC, House JI, Holland EA (2005) Long-term sensitivity of soil carbon turnover to warming. Nature 433: 298−301
- Yan Y, Cao J, Yang H, Yin H, Liang Y, et al. (2012) The impact of different soil types on soil organic carbon pool and turnover in Karst Area (in Chinese). J Soil Water Conserv 26: 144–149.
- Yin Y, Cai Z (2007) Decomposition rates of organic carbon in whole soiland heavy fraction of red soil incorporated with maize stalks using carbon-13 natural abundance (in Chinese).Acta Pedol Sin 44: 1022–1027.
- Wang W, Zeng W, Chen W, Zeng H, Fang J (2013) Soil respiration and organic carbon dynamics with grassland conversions to woodlands in temperate China. PLoS one 8: e71986
- Schrumpf M, Kaiser K (2015) Large differences in estimates of soil organic carbon turnover in density fractions by using single and repeated radiocarbon inventories. Geoderma 239: 168–178
- Hopkins FM, Torn MS, Trumbore SE (2012) Warming accelerates decomposition of decades-old carbon in forest soils. P Natl Acad Sci USA 109: 10152-10153
- Mikutta R, Kleber M, Kaiser K, Jahn R (2005) Organic matter removal from soils using hydrogen peroxide, sodium hypochlorite, and disodium peroxodisulfate. Soil Sci Soc Am J 69: 120–135
- Sollins P, Swanston C, Kleber M, Filley T, Kramer M, et al. (2006) Organic C and N stabilization in a forestsoil: Evidence from sequential density fractionation. Soil Biol Biochem 38: 3313–3324
- Tao S, Eglinton TI, Montluçon DB, McIntyre C, Zhao M (2015) Pre-aged soil organic carbon as a major component of the Yellow River suspended load: Regional significance and global relevance. Earth Planet Sci Lett 414: 77–86
- Zhou W, Chen M (2009) Development of radiocarbon dating in China over the past 50 years. Radiocarbon 50: 91− 107
- Khosh MS, Xu X, Trumbore SE (2010) Small-mass graphite preparation by sealed tube zinc reduction method for AMS 14C measurements. Nucl Instrum Meth Phys Res 268: 927−930
- Linares R, Macario KD, Santos GM, Carvalho C, Dos Santos HC, et al. (2015) Radiocarbon measurements at LAC-UFF: Recent performance. Nucl Instrum Meth B 361:341-345
- Yates A, Smith AM, Parr J, Scheffers A, Joannes-Boyau R (2014) AMS dating of ancient plant residues from experimental stone tools: a pilot study. J Archaeol Sci 49: 595–602
- Yates A, Smith, AM, Bertuch F, Gehlen B, Gramsch B, et al. (2015) Radiocarbon-dating adhesive and wooden residues from stone tools by Accelerator Mass Spectrometry (AMS): Challenges and insights encountered in a case study. J Archaeol Sci 61: 45–58
- Lehmann J (2007) A handful of carbon. Nature 447: 143−144
- Wu W, Yang M, Feng Q, Mcgrouther K, Wang H, et al. (2012) Chemical characterization of rice straw-derived biochar for soil amendment. Biomass Bioenerg 47: 268−276
- Lu W, Ding W, Zhang J, Li Y, Luo J, et al. (2014) Biochar suppressed the decomposition of organic carbon in a cultivated sandy loam soil: A negative priming effect. Soil Biol Biochem 76: 12–21
- Ouyang L, Yu L, Zhang R (2014) Effects of amendment of different biochars on soil carbon mineralisation and sequestration. Soil Res 51: 46−54
- Yin Y, He X, Gao R, Ma H, Yang Y (2014) Effects of rice straw and its biochar addition on soil labile carbon and soil organic carbon. J Integr Agr 13: 491–498
- Huang Y, Chiueh P, Shih C, Lo S, Sun L, et al. (2015) Microwave pyrolysis of rice straw to produce biochar as an adsorbent for CO2 capture. Energy 84:75-82
- Zhang Q, Du Z, Lou Y, He X (2015) A one-year short-term biochar application improved carbon accumulation in large macroaggregate fractions. Catena 127: 26–31
- Woolf D (2008) Biochar as a soil amendment: A review of the environmental implication. University of Swansea
- Singh R, Babu JN, Kumar R, Srivastava P, Singh P, et al. (2015) Multifaceted application of crop residue biochar as a tool for sustainable agriculture: An ecological perspective. Ecol Eng 77: 324–347
- Wu W, Sun X, Dong D, Wang H (2015) Environmental effects of biochar in soil (in Chinese). Science Press, Beijing.
- Lorenz K, Lal R (2005) The depth distribution of organic soil carbon in relation to land use and management and the potential of carbon sequestration in subsoil horizons. Adv Agron 88: 35–66
Citation: Cai M, Tan W, Wang L, Xi B, Zhang L, et al. (2018) What Should we do in the Context of Land Use Change Occurring Frequently in China? J Earth Sci Clim Change 9: 454. DOI: 10.4172/2157-7617.1000454
Copyright: © 2018 Cai M, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Select your language of interest to view the total content in your interested language
Share This Article
Open Access Journals
- Total views: 2582
- [From(publication date): 0-2018 - Jun 30, 2022]
- Breakdown by view type
- HTML page views: 2102
- PDF downloads: 480