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RESEARCH ARTICLE

Changes of soil carbon along a topo-climatic gradient in rangelands of Iran: insights from 14C mean residence time and δ13C

Alireza Owji A B , Ahmad Landi A , Saeed Hojati A and Maral Khodadadi https://orcid.org/0000-0001-5599-4071 C *
+ Author Affiliations
- Author Affiliations

A Department of Soil Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran.

B Department of Water and Soil, Fars Agricultural Organization, Shiraz, Iran.

C Department of Geology and Environmental Earth Science, Miami University, Oxford, OH, USA.

* Correspondence to: khodadm@miamioh.edu

Handling Editor: Samuel Abiven

Soil Research 62, SR23015 https://doi.org/10.1071/SR23015
Submitted: 31 January 2023  Accepted: 13 February 2024  Published: 1 March 2024

© 2024 The Author(s) (or their employer(s)). Published by CSIRO Publishing

Abstract

Context

Soils can be the largest terrestrial carbon source and a potential sink of atmospheric CO2. Soil organic carbon (SOC) dynamics can be unravelled by 14C-derived mean residence times (MRT).

Aims

We aimed to understand SOC dynamics in surface and subsurface soils along a topo-climatic gradient in the rangelands of Khuzestan Province, Iran.

Methods

Study sites were selected under two contrasting regional climates in Izeh (MAT + 19.2°C, MAP 623 mm) and Ramhormoz (MAT + 27.5°C, MAP 200 mm). Soil physicochemical properties, SOC forms, and 14C MRT and δ13C signatures were determined in the control profiles.

Key results

The average MRT up to 1 m depth in Izeh and Ramhormoz were 2980 and 6582 years before present, respectively. On average, a loss of 300 Mg C ha−1 in SOC stocks and a rise of 430 years in SOC MRT up to 1 m can be expected per 1°C increase in MAT, 50 mm reduction in MAP, and 100 m decrease in elevation, highlighting the potential significance of MAT in SOC dynamics. Using optimistic and pessimistic carbon emission scenarios, carbon emissions in the upland areas were projected to be between 50 and 100 Mg C ha−1 over 80 years.

Conclusions

While the most influential element on SOC stock and its relative age was likely the temperature, other factors like erosion and deposition processes can cause enhanced SOC dislocation along the topo-climatic gradient.

Implications

Soil carbon pools stabilised for centuries to millennia are susceptible to alterations due to climate and land cover change.

Keywords: biomass, clay mineralogy, erosion and deposition processes, future carbon emissions, grazed pasture, Khuzestan, organic carbon forms, topographic position.

References

Abtahi A (1977) Effect of a saline and alkaline ground water on soil genesis in semiarid Southern Iran. Soil Science Society of America Journal 41, 583-588.
| Crossref | Google Scholar |

Anonymous (2015) Yearbook of meteorological status of Khuzestan Province, Iranian Meteorological Organization. Research Division of Khuzestan Province. (in Persian)

Azarnivand H, Namjooyan R, Arzani H, Jafari M, Zare chahoki M (2007) Locate and programs rangeland restore and reform with using from GIS and compared that with proposed projects in Range Management rangeland projects in Lar region. Rangeland Journal 3(2), 159-168.
| Google Scholar |

Bailey VL, Pries CH, Lajtha K (2019) What do we know about soil carbon destabilization? Environmental Research Letters 14, 083004.
| Crossref | Google Scholar |

Balesdent J, Wagner GH, Mariotti A (1988) Soil organic matter turnover in long-term field experiments as revealed by carbon-13 natural abundance. Soil Science Society of America Journal 52(1), 118-124.
| Crossref | Google Scholar |

Banaii MH (1998) Soil moisture and temperature regimes map. Soil and Water Research Institute of Iran, Tehran. (in Persian)

Batjes NH (1996) Total carbon and nitrogen in the soils of the world. European Journal of Soil Science 47(2), 151-163.
| Crossref | Google Scholar |

Benbi DK, Brar K, Toor AS, Singh P (2015) Total and labile pools of soil organic carbon in cultivated and undisturbed soils in northern India. Geoderma 237–238, 149-158.
| Crossref | Google Scholar |

Benner R, Fogel ML, Sprague EK, Hodson RE (1987) Depletion of 13C in lignin and its implications for stable carbon isotope studies. Nature 329(6141), 708-710.
| Crossref | Google Scholar |

Berhe AA, Harte J, Harden JW, Torn MS (2007) The significance of the erosion-induced terrestrial carbon sink. BioScience 57(4), 337-346.
| Crossref | Google Scholar |

Berry SC, Varney GT, Flanagan LB (1997) Leaf δ13C in Pinus resinosa trees and understory plants: variation associated with light and CO2 gradients. Oecologia 109(4), 499-506.
| Crossref | Google Scholar | PubMed |

Blair GJ, Lefroy RDB, Lisle L (1995) Soil carbon fractions based on their degree of oxidation, and the development of a carbon management index for agricultural systems. Australian Journal of Agricultural Research 46(7), 1459-1466.
| Crossref | Google Scholar |

Breuning-Madsen H, Elberling B, Balstroem T, Holst M, Freudenberg M (2009) A comparison of soil organic carbon stock in ancient and modern land use systems in Denmark. European Journal of Soil Science 60(1), 55-63.
| Crossref | Google Scholar |

Brevik EC (2012) Soils and climate change: gas fluxes and soil processes. Soil Horizons 53(4), 12-23.
| Crossref | Google Scholar |

Brevik EC, Homburg JA (2004) A 5000 year record of carbon sequestration from a coastal lagoon and wetland complex, Southern California, USA. Catena 57(3), 221-232.
| Crossref | Google Scholar |

Brevik EC, Cerdà A, Mataix-Solera J, Pereg L, Quinton JN, Six J, Van Oost K (2015) The interdisciplinary nature of SOIL. Soil 1(1), 117-129.
| Crossref | Google Scholar |

Buyanovsky GA, Aslam M, Wagner GH (1994) Carbon turnover in soil physical fractions. Soil Science Society of America Journal 58(4), 1167-1173.
| Crossref | Google Scholar |

Carter MR (2002) Soil quality for sustainable land management: organic matter and aggregation interactions that maintain soil functions. Agronomy Journal 94(1), 38-47.
| Crossref | Google Scholar |

Chambers JC, Brown RE (1983) Methods for vegetation sampling and analysis on revegetated mined lands. intermountain forest and range experiment station. General Technical Report. INT.151 Ogden, UT. U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. p. 57.

Chapman HD (1965) Cation-exchange capacity. In ‘Methods of soil analysis: Part 2 Chemical and microbiological properties’. Agronomy No. 9. (Ed. CA Black) pp. 891–901. (American Society of Agronomy)

Chen S, Huang Y, Zou J, Shi Y (2013) Mean residence time of global topsoil organic carbon depends on temperature, precipitation and soil nitrogen. Global and Planetary Change 100, 99-108.
| Crossref | Google Scholar |

Chen L, Smith P, Yang Y (2015) How has soil carbon stock changed over recent decades? Global Change Biology 21(9), 3197-3199.
| Crossref | Google Scholar | PubMed |

Chen J, Zhou X, Wang J, Hruska T, Shi W, Cao J, Zhang B, Xu G, Chen Y, Luo Y (2016) Grazing exclusion reduced soil respiration but increased its temperature sensitivity in a Meadow Grassland on the Tibetan Plateau. Ecology and Evolution 6(3), 675-687.
| Crossref | Google Scholar | PubMed |

Chen L, Fang K, Wei B, Qin S, Feng X, Hu T, Ji C, Yang Y (2021) Soil carbon persistence governed by plant input and mineral protection at regional and global scales. Ecology Letters 24(5), 1018-1028.
| Crossref | Google Scholar | PubMed |

Coplen TB (1995) Reporting of stable carbon, hydrogen, and oxygen isotopic abundances. In ‘Reference and intercomparison materials for stable isotopes of light elements, 825’. pp. 31–34. (IAEA)

Culman SW, Snapp SS, Freeman MA, Schipanski ME, Beniston J, Lal R, Drinkwater LE, Franzluebbers AJ, Glover JD, Grandy AS, Lee J, Six J, Maul JE, Mirksy SB, Spargo JT, Wander MM (2012) Permanganate oxidizable carbon reflects a processed soil fraction that is sensitive to management. Soil Science Society of America Journal 76(2), 494-504.
| Crossref | Google Scholar |

Dai W, Huang Y (2006) Relation of soil organic matter concentration to climate and altitude in zonal soils of China. Catena 65(1), 87-94.
| Crossref | Google Scholar |

Dai E, Zhai R, Ge Q, Wu X (2014) Detecting the storage and change on topsoil organic carbon in grasslands of Inner Mongolia from 1980s to 2010s. Journal of Geographical Sciences 24(6), 1035-1046.
| Crossref | Google Scholar |

Davidson EA, Janssens IA (2006) Temperature sensitivity of soil carbon decomposition and feedbacks to climate change. Nature 440(7081), 165-173.
| Crossref | Google Scholar | PubMed |

Dialynas YG, Bastola S, Bras RL, Billings SA, Markewitz D, Richter DdB (2016) Topographic variability and the influence of soil erosion on the carbon cycle. Global Biogeochemical Cycles 30(5), 644-660.
| Crossref | Google Scholar |

Dixon JB, Weed SB (1989) ‘Minerals in soil environments.’ (Soil Science Society of America: Madison, WI, USA)

Eglinton TI, Galy VV, Hemingway JD, Feng X, Bao H, Blattmann TM, Dickens AF, Gies H, Giosan L, Haghipour N, Hou P, Lupker M, McIntyre CP, Montluçon DB, Peucker-Ehrenbrink B, Ponton C, Schefuß E, Schwab MS, Voss BM, Wacker L, Wu Y, Zhao M (2021) Climate control on terrestrial biospheric carbon turnover. Proceedings of the National Academy of Sciences 118(8), e2011585118.
| Crossref | Google Scholar |

Eskandari N, Alizadeh A, Mahdavi F (2008) Policies of Range Management in Iran. Rangeland Technical Office. (in Persian)

Fu J, Gasche R, Wang N, Lu H, Butterbach-Bahl K, Kiese R (2019) Dissolved organic carbon leaching from montane grasslands under contrasting climate, soil and management conditions. Biogeochemistry 145(1), 47-61.
| Crossref | Google Scholar |

Gee GW, Bauder JW (1986) Particle size analysis. In ‘Methods of soil analysis, Part 1’. (Ed. A Klute) pp. 383–411. (American Society of Agronomy Inc.: Madison, WI, USA)

Gellrich M, Zimmermann NE (2007) Investigating the regional-scale pattern of agricultural land abandonment in the Swiss mountains: a spatial statistical modelling approach. Landscape and Urban Planning 79(1), 65-76.
| Crossref | Google Scholar |

Geraei DS, Hojati S, Landi A, Cano AF (2016) Total and labile forms of soil organic carbon as affected by land use change in southwestern Iran. Geoderma Regional 7(1), 29-37.
| Crossref | Google Scholar |

Ghani A, Dexter M, Perrott KW (2003) Hot-water extractable carbon in soils: a sensitive measurement for determining impacts of fertilisation, grazing and cultivation. Soil Biology and Biochemistry 35(9), 1231-1243.
| Crossref | Google Scholar |

Haynes RJ (2005) Labile organic matter fractions as central components of the quality of agricultural soils: an overview. Advances in Agronomy 85, 221-268.
| Crossref | Google Scholar |

Hemingway JD, Rothman DH, Grant KE, Rosengard SZ, Eglinton TI, Derry LA, Galy VV (2019) Mineral protection regulates long-term global preservation of natural organic carbon. Nature 570(7760), 228-231.
| Crossref | Google Scholar | PubMed |

Hernanz JL, López R, Navarrete L, Sánchez-Girón V (2002) Long-term effects of tillage systems and rotations on soil structural stability and organic carbon stratification in semiarid central Spain. Soil and Tillage Research 66(2), 129-141.
| Crossref | Google Scholar |

Hou Y, Chen Y, Chen X, He K, Zhu B (2019) Changes in soil organic matter stability with depth in two alpine ecosystems on the Tibetan Plateau. Geoderma 351, 153-162.
| Crossref | Google Scholar |

Hou Y, He K, Chen Y, Zhao J, Hu H, Zhu B (2021) Changes of soil organic matter stability along altitudinal gradients in Tibetan alpine grassland. Plant and Soil 458, 21-40.
| Crossref | Google Scholar |

IPCC (Intergovernmental Panel on Climate Change), Working Group I (2007) Climate change 2007: the physical science basis. In ‘Contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change’. (Eds S Solomon, D Qin, M Manning, Z Chen, M Marquis, KB Averyt, M Tignor, HL Miller) p. 996. (Cambridge University Press: Cambridge, United Kingdom and New York, NY, USA)

Jobbágy EG, Jackson RB (2000) The vertical distribution of soil organic carbon and its relation to climate and vegetation. Ecological Applications 10(2), 423-436.
| Crossref | Google Scholar |

Kalbitz K, Solinger S, Park J-H, Michalzik B, Matzner E (2000) Controls on the dynamics of dissolved organic matter in soils: a review. Soil Science 165(4), 277-304.
| Crossref | Google Scholar |

Kelly EF, Amundson RG, Marino BD, Deniro MJ (1991) Stable isotope ratios of carbon in phytoliths as a quantitative method of monitoring vegetation and climate change. Quaternary Research 35(2), 222-233.
| Crossref | Google Scholar |

Kindler R, Siemens J, Kaiser K, Walmsley DC, Bernhofer C, Buchmann N, et al. (2011) Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance. Global Change Biology 17, 1167-1185.
| Crossref | Google Scholar |

Kögel-Knabner I, Guggenberger G, Kleber M, Kandeler E, Kalbitz K, Scheu S, Eusterhues K, Leinweber P (2008) Organo-mineral associations in temperate soils: integrating biology, mineralogy, and organic matter chemistry. Journal of Plant Nutrition and Soil Science 171(1), 61-82.
| Crossref | Google Scholar |

Körner C, Farquhar GD, Wong SC (1991) Carbon isotope discrimination by plants follows latitudinal and altitudinal trends. Oecologia 88(1), 30-40.
| Crossref | Google Scholar | PubMed |

Krull E, Bray S, Harms B, Baxter N, Bol R, Farquhar G (2007) Development of a stable isotope index to assess decadal-scale vegetation change and application to woodlands of the Burdekin catchment, Australia. Global Change Biology 13(7), 1455-1468.
| Crossref | Google Scholar |

Lal R (2006) Impacts of climate on soil systems and of soil systems on climate. In ‘Biological approaches to sustainable soil systems’ (Eds N Uphoff, AS Ball, E Fernandes, et al.) pp. 617–636. (CRC Press Taylor & Francis Group)

Landi A, Anderson DW, Mermut AR (2003) Organic carbon storage and stable isotope composition of soils along a grassland to forest environmental gradient in Saskatchewan. Canadian Journal of Soil Science 83(4), 405-414.
| Crossref | Google Scholar |

Lasanta T, González-Hidalgo JC, Vicente-Serrano SM, Sferi E (2006) Using landscape ecology to evaluate an alternative management scenario in abandoned Mediterranean mountain areas. Landscape and Urban Planning 78(1–2), 101-114.
| Crossref | Google Scholar |

Lefrançois J, Grimaldi C, Gascuel-Odoux C, Gilliet N (2007) Suspended sediment and discharge relationships to identify bank degradation as a main sediment source on small agricultural catchments. Hydrological Processes: An International Journal 21(21), 2923-2933.
| Crossref | Google Scholar |

Lemenih M, Itanna F (2004) Soil carbon stocks and turnovers in various vegetation types and arable lands along an elevation gradient in southern Ethiopia. Geoderma 123(1–2), 177-188.
| Crossref | Google Scholar |

Lenzi MA, Marchi L (2000) Suspended sediment load during floods in a small stream of the Dolomites (Northeastern Italy). Catena 39(4), 267-282.
| Crossref | Google Scholar |

Loeppert RH, Suarez DL (1996) Carbonate and gypsum. In ‘Methods of soil analysis, Part 3’. (Ed. DL Sparks) pp. 437–474. (American Society of Agronomy Inc.: Madison, WI, USA)

Lorenz K, Lal R, Shipitalo MJ (2008) Chemical stabilization of organic carbon pools in particle size fractions in no-till and meadow soils. Biology and Fertility of Soils 44(8), 1043-1051.
| Crossref | Google Scholar |

Lützow MV, Kögel-Knabner I, Ekschmitt K, Matzner E, Guggenberger G, Marschner B, Flessa H (2006) Stabilization of organic matter in temperate soils: mechanisms and their relevance under different soil conditions – a review. European Journal of Soil Science 57(4), 426-445.
| Crossref | Google Scholar |

Mathieu JA, Hatté C, Balesdent J, Parent É (2015) Deep soil carbon dynamics are driven more by soil type than by climate: a worldwide meta-analysis of radiocarbon profiles. Global Change Biology 21(11), 4278-4292.
| Crossref | Google Scholar | PubMed |

Mermut AR, Acton DF (1984) The age of some Holocene soils on the Ear Lake terraces in Saskatchewan. Canadian Journal of Soil Science 64, 163-172.
| Crossref | Google Scholar |

Minasny B, Malone BP, McBratney AB, Angers DA, Arrouays D, Chambers A, et al. (2017) Soil carbon 4 per mille. Geoderma 292, 59-86.
| Crossref | Google Scholar |

Mohammadi S, Karimzadeh H, Alizadeh M (2018) Spatial estimation of soil erosion in Iran using RUSLE model. Iranian Journal of Ecohydrology 5(2), 551-569.
| Crossref | Google Scholar |

Monreal CM, Schulten H-R, Kodama H (1997) Age, turnover and molecular diversity of soil organic matter in aggregates of a Gleysol. Canadian Journal of Soil Science 77(3), 379-388.
| Crossref | Google Scholar |

Mujuru L, Mureva A, Velthorst EJ, Hoosbeek MR (2013) Land use and management effects on soil organic matter fractions in Rhodic Ferralsols and Haplic Arenosols in Bindura and Shamva districts of Zimbabwe. Geoderma 209-210, 262-272.
| Crossref | Google Scholar |

Muñoz-Rojas M, Jordán A, Zavala LM, De la Rosa D, Abd-Elmabod SK, Anaya-Romero M (2012) Organic carbon stocks in Mediterranean soil types under different land uses (Southern Spain). Solid Earth 3(2), 375-386.
| Crossref | Google Scholar |

Muñoz-Rojas M, Jordán A, Zavala LM, González-Peñaloza FA, De la Rosa D, Pino-Mejias R, Anaya-Romero M (2013) Modelling soil organic carbon stocks in global change scenarios: a CarboSOIL application. Biogeosciences 10(12), 8253-8268.
| Crossref | Google Scholar |

Neff JC, Reynolds RL, Belnap J, Lamothe P (2005) Multi-decadal impacts of grazing on soil physical and biogeochemical properties in southeast Utah. Ecological Applications 15(1), 87-95.
| Crossref | Google Scholar |

Nelson RE (1982) Carbonate and gypsum. In ‘Methods of soil analysis, Part 2. Chemical and microbiological properties’. Agronomy series 9. (2nd edn). (Eds AL Page, RH Miller, DR Keeney) pp. 181–197. (American Society of Agronomy: Madison, WI)

Nelson DA, Sommers L (1983) Total carbon, organic carbon and organic matter. In ‘Methods of soil analysis’. (Ed. AL Page) pp. 539–579. (SSSA: Madison, WI, USA)

Nikghadam N, Mofidi Shemirani SJ, Taherbaz M (2015) Analysis of climate classifications in southern Iran based on Koppen-trewartha method and Givonis’ bioclimatic index. Armanshahr Architecture and Urban Development 8(15), 119-130 (in Persian).
| Google Scholar |

Nunes JP, Carvalho-Santos C (2015) Comparing the impacts of land-use management and climate change on soil erosion: a modeling exercise for humid and dry Mediterranean regions in Portugal. In ‘EGU general assembly conference abstracts’. p. 5411.

Nunes JP, Lima JC, Bernard-Jannin L, Veiga S, Rodríguez-Blanco ML, Sampaio E, Batista DP, Zhang R, Rial-Rivas ME, Moreira M, Santos JM (2012) Impacts of climate change on soil erosion in Portuguese watersheds with contrasting Mediterranean climates and agroforestry practices. In ‘EGU general assembly conference abstracts’. p. 12711.

Ohno T, Heckman KA, Plante AF, Fernandez IJ, Parr TB (2017) 14C mean residence time and its relationship with thermal stability and molecular composition of soil organic matter: a case study of deciduous and coniferous forest types. Geoderma 308, 1-8.
| Crossref | Google Scholar |

Owji A, Landi A, Hojati S (2017) Studying soil clay mineralogy of soils in Dimeh rangelands of Khuzestan province. In ‘15th Iranian Soil Science Congress’, Iran.

Paul EA, Collins HP, Leavitt SW (2001) Dynamics of resistant soil carbon of Midwestern agricultural soils measured by naturally occurring 14C abundance. Geoderma 104(3-4), 239-256.
| Crossref | Google Scholar |

Paustian K, Lehmann J, Ogle S, Reay D, Robertson GP, Smith P (2016) Climate-smart soils. Nature 532(7597), 49-57.
| Crossref | Google Scholar | PubMed |

Poeplau C, Don A, Schneider F (2021) Roots are key to increasing the mean residence time of organic carbon entering temperate agricultural soils. Global Change Biology 27(19), 4921-4934.
| Crossref | Google Scholar | PubMed |

Rabbi SMF, Hua Q, Daniel H, Lockwood PV, Wilson BR, Young IM (2013) Mean residence time of soil organic carbon in aggregates under contrasting land uses based on radiocarbon measurements. Radiocarbon 55(1), 127-139.
| Crossref | Google Scholar |

Ramsey CB (2017) Methods for summarizing radiocarbon datasets. Radiocarbon 59(6), 1809-1833.
| Crossref | Google Scholar |

Reimer PJ, Bard E, Bayliss A, Beck JW, Blackwell PG, Ramsey CB, et al. (2013) IntCal13 and Marine13 radiocarbon age calibration curves 0–50,000 years cal BP. Radiocarbon 55(4), 1869-1887.
| Crossref | Google Scholar |

Rhoades JD (1996) Salinity: Electrical conductivity and total dissolved solids. In ‘Methods of soil analysis: Part 3 chemical methods, Vol. 5’. (Eds DL Sparks, AL Page, PA Helmke, et al.) pp. 417–435. (Soil Science Society of America, Inc., American Society of Agronomy, Inc.)

Schmidt MWI, Torn MS, Abiven S, Dittmar T, Guggenberger G, Janssens IA, Kleber M, Kögel-Knabner I, Lehmann J, Manning DAC, Nannipieri P, Rasse DP, Weiner S, Trumbore SE (2011) Persistence of soil organic matter as an ecosystem property. Nature 478(7367), 49-56.
| Crossref | Google Scholar | PubMed |

Schöning I, Morgenroth G, Kögel-Knabner I (2005) O/N-alkyl and alkyl C are stabilised in fine particle size fractions of forest soils. Biogeochemistry 73(3), 475-497.
| Crossref | Google Scholar |

Schweizer M, Fear J, Cadisch G (1999) Isotopic (13C) fractionation during plant residue decomposition and its implications for soil organic matter studies. Rapid Communications in Mass Spectrometry 13(13), 1284-1290.
| Crossref | Google Scholar | PubMed |

Shahzad T, Rashid MI, Maire V, Barot S, Perveen N, Alvarez G, Mougin C, Fontaine S (2018) Root penetration in deep soil layers stimulates mineralization of millennia-old organic carbon. Soil Biology and Biochemistry 124, 150-160.
| Crossref | Google Scholar |

Shen Y, Chapelle FH, Strom EW, Benner R (2015) Origins and bioavailability of dissolved organic matter in groundwater. Biogeochemistry 122(1), 61-78.
| Crossref | Google Scholar |

Shi Z, Allison SD, He Y, Levine PA, Hoyt AM, Beem-Miller J, Zhu Q, Wieder WR, Trumbore S, Randerson JT (2020) The age distribution of global soil carbon inferred from radiocarbon measurements. Nature Geoscience 13(8), 555-559.
| Crossref | Google Scholar |

Soil Survey Staff (2014) ‘Keys to soil taxonomy.’ 10th edn. p. 333. (U. S. Department of Agriculture -Natural Resources Conservation Service, U. S. Government Printing Office: Washington)

Souza GPd, Figueiredo CCd, Sousa DMGd (2016) Relationships between labile soil organic carbon fractions under different soil management systems. Scientia Agricola 73, 535-542.
| Crossref | Google Scholar |

Staddon PL (2004) Carbon isotopes in functional soil ecology. Trends in Ecology & Evolution 19(3), 148-154.
| Crossref | Google Scholar | PubMed |

Stevenson BA, Kelly EF, McDonald EV, Busacca AJ (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(1-2), 37-47.
| Crossref | Google Scholar |

Thomas GW (1996) Soil pH and soil acidity. In ‘Methods of soil analysis, Part 3: chemical methods’. SSSA Book Series Number 5. (Ed. DL Sparks) pp. 475–490. (Soil Science Society of America: Madison, WI)

Torn MS, Kleber M, Zavaleta ES, Zhu B, Field CB, Trumbore SE (2013) A dual isotope approach to isolate soil carbon pools of different turnover times. Biogeosciences 10, 8067-8081.
| Crossref | Google Scholar |

Trumbore S (2009) Radiocarbon and soil carbon dynamics. Annual Review of Earth and Planetary Sciences 37(1), 47-66.
| Crossref | Google Scholar |

Trumbore SE, Vogel JS, Southon JR (1989) AMS 14C measurements of fractionated soil organic matter: an approach to deciphering the soil carbon cycle. Radiocarbon 31(3), 644-654.
| Crossref | Google Scholar |

Vance ED, Brookes PC, Jenkinson DS (1987) An extraction method for measuring soil microbial biomass C. Soil Biology and Biochemistry 19(6), 703-707.
| Crossref | Google Scholar |

Van Oost K, Quine TA, Govers G, De Gryze S, Six J, Harden JW, Ritchie JC, McCarty GW, Heckrath G, Kosmas C, Giraldez JV, da Silva JRM, Merckx R (2007) The impact of agricultural soil erosion on the global carbon cycle. Science 318(5850), 626-629.
| Crossref | Google Scholar | PubMed |

Veum KS, Goyne KW, Motavalli PP, Udawatta RP (2009) Runoff and dissolved organic carbon loss from a paired-watershed study of three adjacent agricultural watersheds. Agriculture, Ecosystems & Environment 130(3–4), 115-122.
| Crossref | Google Scholar |

Walkley A, Black IA (1934) An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Science 37(1), 29-38.
| Crossref | Google Scholar |

Wang Y, Amundson R, Trumbore S (1999) The impact of land use change on C turnover in soils. Global Biogeochemical Cycles 13(1), 47-57.
| Crossref | Google Scholar |

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. Journal of Environmental Sciences 24(3), 387-395.
| Crossref | Google Scholar |

Wattel-Koekkoek EJW, Buurman P, Van Der Plicht J, Wattel E, Van Breemen N (2003) Mean residence time of soil organic matter associated with kaolinite and smectite. European Journal of Soil Science 54(2), 269-278.
| Crossref | Google Scholar |

Wedin DA, Tieszen LL, Dewey B, Pastor J (1995) Carbon isotope dynamics during grass decomposition and soil organic matter formation. Ecology 76(5), 1383-1392.
| Crossref | Google Scholar |

Wei J-B, Xiao D-N, Zeng H, Fu Y-K (2008) Spatial variability of soil properties in relation to land use and topography in a typical small watershed of the black soil region, northeastern China. Environmental Geology 53(8), 1663-1672.
| Crossref | Google Scholar |

Wiesmeier M, Schad P, Von Lützow M, Poeplau C, Spörlein P, Geuß U, Hangen E, Reischl A, Schilling B, Kögel-Knabner I (2014) Quantification of functional soil organic carbon pools for major soil units and land uses in southeast Germany (Bavaria). Agriculture, Ecosystems & Environment 185, 208-220.
| Crossref | Google Scholar |

Wiesmeier M, Lützow MV, Spörlein P, Geuß U, Hangen E, Reischl A, Schilling B, Kögel-Knabner I (2015) Land use effects on organic carbon storage in soils of Bavaria: the importance of soil types. Soil and Tillage Research 146, 296-302.
| Crossref | Google Scholar |

Wilson MJ (1999) The origin and formation of clay minerals in soils: past, present and future perspectives. Clay Minerals 34(1), 7-25.
| Crossref | Google Scholar |

World Reference Base for Soil Resources (2014) ‘A framework for international classification, correlation and communication.’ (World Reference Base for Soil Resources: Rome, Italy)

Yoo K, Amundson R, Heimsath AM, Dietrich WE (2006) Spatial patterns of soil organic carbon on hillslopes: integrating geomorphic processes and the biological C cycle. Geoderma 130(1–2), 47-65.
| Crossref | Google Scholar |