Oct 17, 2009 - The effect of conversion from forest-to-pasture upon soil carbon stocks has been intensively dis- cussed, but few studies focus on how this land- ...
Ecosystems (2009) 12: 1212–1221 DOI: 10.1007/s10021-009-9288-7 2009 Springer Science+Business Media, LLC
Soil Carbon Turnover Measurement by Physical Fractionation at a Forest-to-Pasture Chronosequence in the Brazilian Amazon Carolina C. Lisboa,1* Richard T. Conant,2 Michelle L. Haddix,2 Carlos Eduardo P. Cerri,1 and Carlos C. Cerri3 1
Department of Soil Science, Escola Superior de Agricultura ‘‘Luiz de Queiroz’’, Universidade de Sa˜o Paulo, Avenida Padua Dias, 11, Piracicaba, SP 13418-900, Brazil; 2Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado 805231499, USA; 3Centro de Energia Nuclear na Agricultura, Universidade de Sa˜o Paulo, Piracicaba, SP 13400-970, Brazil
ABSTRACT The microaggregate comprised the highest soil C content after the conversion from forest-to-pasture. The C content of the d-silt fraction decreased with time since conversion to pasture. Forest-derived C remained in all fractions with the highest concentration in the finest fractions, with the largest proportion of forest-derived soil C associated with clay minerals. Results from this work indicate that microaggregate formation is sensitive to changes in management and might serve as an indicator for management-induced soil carbon changes, and the soil C changes in the fractions are dependent on soil texture.
The effect of conversion from forest-to-pasture upon soil carbon stocks has been intensively discussed, but few studies focus on how this land-use change affects carbon (C) distribution across soil fractions in the Amazon basin. We investigated this in the 20 cm depth along a chronosequence of sites from native forest to three successively older pastures. We performed a physicochemical fractionation of bulk soil samples to better understand the mechanisms by which soil C is stabilized and evaluate the contribution of each C fraction to total soil C. Additionally, we used a two-pool model to estimate the mean residence time (MRT) for the slow and active pool C in each fraction. Soil C increased with conversion from forest-to-pasture in the particulate organic matter (>250 lm), microaggregate (53–250 lm), and d-clay ( 250 lm). Materials passing the 250 lm sieve were flushed by a continuous water flow out of the shaker onto a 53 lm sieve. The materials retained on the 53 lm sieve were wet sieved for 2 min at approximately 25 cycles per minute, and then finer material was gently washed off to isolate the microaggregate fraction (53–250 lm). The suspension passing the 53 lm sieve was centrifuged to isolate the easily dispersed silt-sized fraction (d-silt, 2–53 lm). The supernatant was then flocculated using 0.25 M MgCl2 and CaCl2 and centrifuged to isolate the easily dispersed clay-sized fraction (d-clay, 250 lm) (g soil fraction kg whole soil-1)
Microaggregate (53–250 lm) (g soil fraction kg whole soil-1)
d-Silt (2–53 lm) (g soil fraction kg whole soil-1)
d-Clay (250 lm) (&) 0.15 0.34 0.33 0.31
-28.6 -17.9 -18.6 -18.8
± ± ± ±
0.11 0.47 0.42 0.35
d13C Value for Bulk Soil Samples and Fractions The d13C value in the bulk soil increased from 27.9& in the forest to -17.7& in the oldest pasture (Table 3). The forest-to-pasture conversion and the increasing age of pasture resulted in progressive enrichment of 13C value in the bulk soil and microaggregate, d-silt, and d-clay fractions. Unexpectedly, the POM fraction was more enriched in 13C value for the youngest pasture follow by pasture converted in 1972 and 1911.
Turnover The MRTs varied between 210 and more than 2500 years for the d-silt and d-clay fractions, respectively (Table 4). There was variation in MRT between all size fractions. The MRTs for whole soil was slightly lower than that of the microaggregate
Microaggregate (53–250 lm) (&) -27.6 -18.9 -17.9 -17.4
± ± ± ±
0.17 0.14 0.14 0.13
d-Silt (2–53 lm) (&) -27.5 -19.5 -18.8 -17.8
± ± ± ±
0.07 0.06 0.55 0.05
d-Clay (250 lm) Microaggregate (53–250 lm) d-silt (2–53 lm) d-clay (2500
r2
Eq. parameters a
ka
s
ks
0.52 0.14 0.67 1.52 1.17
0.800 1.327 0.800 0.800 0.802
0.430 0.138 0.328 1.240 1.054
0.002 0.001 0.002 0.005 1 9 10-8
0.999 0.676 0.941 0.979 0.860
MRTs mean residence time of slow pool, MRTa mean residence time of active pool, a active pool, ka decomposition rates of active pool, s slow pool, ks decomposition rate of slow pool.
Table 5.
Proportional Loss and Gain of Carbon Across Fractions
Treatment/sites (soil)
Forest Pasture 1989 Pasture 1972 Pasture 1911
Loss forest-derived C (%)
Gain pasture-derived C (%)
POM
Micro
d-Silt
d-Clay
POM
Micro
d-Silt
d-Clay
0 49 aB 35 bB 57 aB
0 43 bB 60 aA 58 aB
0 57 bA 66 aA 71 aA
0 44 bB 60 aA 47 bC
– 165 aA 142 aA 89 bB
– 114 bB 112 bB 146 aA
– 67 bC 68 bC 83 aB
– 85 bC 80 bC 154 aA
Values represent means of four replicates. Different lowercase letters indicate significant differences between soils (rows) within each fraction and different capital letters indicate significant differences between fractions within a soil (columns).
The greatest proportional gain of pasture-derived soil C was found for the POM fraction in the 1989 pasture soil. Pasture converted in 1911 had the greatest proportional gain of pasture-derived soil C in the d-clay fraction, and pastures converted in 1989 and 1972 had the lowest proportional gain of pasture-derived soil C in the microaggregate and dsilt fraction.
DISCUSSION Following conversion from forest to pasture, soil C content, and distribution across the physical fraction changed significantly, consistent with other studies (Feigl and others 1995; Moraes and others 1996; Cerri and others 2004) conducted at Nova Vida Ranch in the southwestern Amazon region. Our data indicate that increases or decreases in soil C source and soil C content at the soil fractions after conversion from forest to pasture seem to be dependent upon soil texture and the recalcitrance of soil C, and are consistent with results reported elsewhere (Neill and Davidson 2000; Davidson and Artaxo 2004; Cerri and others 2007). Our results show that an increase in microaggregate-associated C was the largest contributor to changes in total soil
C content. Microaggregates in these sandy-soils stabilized a large amount of pasture-derived C and retained a large portion of forest-derived microaggregate C. This is consistent with other data showing that physical protection has an important influence on sequestration of C in soils following land-use change (Edwards and Bremner 1967; Elliott 1986; Six and others 2002; Denef and others 2004). Studies published to-date using similar physical fractionation schemes in tropical soils also report that microaggregate formation is sensitive to changes in management and might serve as an indicator for management-induced soil organic carbon changes (Feller and Beare 1997; Denef and others 2004, 2007; Desjardins and others 2004; Zotarelli and others 2007). Our work confirms that microaggregates are important for maintaining native soil C stocks and for sequestering pasturederived soil C. In highly weathered tropical soils, the high concentration of very reactive Fe- and Aloxides foster the formation of mineral-organic matter complexes that are highly stabile, possibly enhancing the stability of newly formed microaggregates (Sørensen 1972; Boudot and others 1988; Dick and Schwertmann 1996; Feller and Beare 1997).
Soil Carbon Turnover Measurement by Physical Fractionation Previous studies of forest-to-pasture conversion on soil C in the Amazon basin reported that large amounts of forest-derived C remained within all fractions even after several years (Chone´ and others 1991; Feigl and others 1995; Desjardins and others 1994, 2004). Desjardins and others (2004) reported that C derived from forest represented 58 to 52% depending on the fraction for the 0–5 cm layer in a sandy soil after 15 years of cultivation in the Eastern Amazon region. Our results showed that forest-derived C varied from 65 to 29% according to the fraction size and pasture age in the 0–20 cm layer. The large amount of forest-derived C we found in the POM fraction within pasture soils—even those converted nearly 100 years before sampling—suggests the presence of charcoal or other recalcitrant debris left after forest burning. The slash and burn methods used to clear the forest vegetation at Nova Vida Ranch (Feigl and others 1995) are commonly used for tropical forest-to-pasture conversion throughout the Amazon basin and beyond. Grac¸a and others (1999) studied charcoal formation from burning forest biomass at Nova Vida Ranch and found that the stock of charcoal formed immediately post-burn was 4.1 Mg C ha-1. Charcoal is considered to be a virtually permanent C stock (Grac¸a and others 1999). Our results indicated a forest-derived POM C stock of 1.13, 0.96, and 0.85 Mg C ha-1 for pastures converted in 1989, 1972, and 1911, respectively, all lower than those reported by Grac¸a and others (1999). We hypothesize that either (1) the charcoal formed post-burn is not a permanent C stock and it is lost through decomposition or erosion or, (2) the charcoal observed by Grac¸a and others (1999) could reside in fractions other than the POM fraction. In accordance with other literature studies (Desjardins and others 1994; Feigl and others 1995; Desjardins and others 2004; Denef and others 2007) our results showed that there was also persistence of forest-derived C in the mineral fractions, with lower forest-derived C content in the d-silt than in the dclay fraction. Additionally, our results showed that the d-clay and d-silt fractions contribute strongly to the increase in total soil C. These results suggest either that greater C input to the soil is preferentially stabilized in the microaggregate fraction or that pasture C inputs better facilitate formation of microaggregates. Tisdall and Oades (1982) mentioned that C contents determine the increase of aggregate formation. However, as found by Lehmann and others (2001) who studied clayey soils from the central Amazon basin, our results indicated that aggregates might not to be held together
1219
primarily by SOM, but might be strongly influenced by mineral particles (silt and clay) as binding agents. This mechanism has been described by Kleber and others (2007), who suggested that the most stable soil C is in the organo-mineral complexes. There is lack of data available for estimating how d13C values would vary among fractions, particularly for pasture soils in which d13C values are driven by a combination of environmental conditions (Krull and Skjemstad 2003). For instance, there is the spatial stratification of isotopic signatures in each fraction, which is a function of distinct discrimination of mixed plant material at different decomposition stages (Balesdent and others 1987; Bernoux and others 1998; Boutton and others 1999; Feigl and others 1995; Desjardins and others 2004). In fact, the dynamics of SOM isotopic fractionation is still not well-understood (Ehleringer and others 2000), contributing to the uncertainty in interpretation of results. The two-pool model with first-order kinetics (Paul and others 1999) has not been used to describe the MRT for SOM pools under tropical soils yet. Our results for this mathematical approach distinguished the MRT for the slow pool C between the POM, microaggregate, d-silt and d-clay fractions and whole soil. This two-pool model did not distinguish the MRT for the active pool C between microagreggate, d-silt, and d-clay or between those fractions and whole soil. The fact that the POM fraction had the longest MRTs suggested the presence of small particles of charcoal or the presence of recalcitrant C material in that fraction. In addition the greatest MRTs for the d-clay fraction suggests the presence of more refractory carbon in this fraction. There are studies with the assumption that different SOM pools have similar decomposition rates (Melillo and others 1995; Burke and others 2003; Friedlingstein and others 2006), whereas other studies (Andreux and others 1990; Bernoux and others 1998; Paul and others 1999; Giardina and Ryan 2000; Davidson and Janssens 2006; Conant and others 2007) have shown that the SOM pools have distinct decomposition rates. The different decomposition rates for SOM pools suggest that it is appropriate to use a two-pool model to estimate the MRT of SOM. We found differences in mass distributions between sites across fractions which reflect small textural differences. This fact is likely attributable to natural spatial variability of the fields because it is not related to pasture age (Moraes and others 1996; Bernoux and others 1998). There was relatively little influence of texture in each site on the weight distribution across fractions. Conversion
1220
C. C. Lisboa and others
from forest-to-pasture resulted in an increase in soil C content for all soil C fractions and altered the C distribution across soil C fractions. The stabilization of the organic matter from pasture vegetation was related to chemical and physical interactions of soil C with mineral soil particles. Loss of forest-derived C, gain of pasture-derived C, and whole soil C distribution across soil C fractions all varied as a function of soil age.
ACKNOWLEDGEMENTS We would like to thank Dan Reuss and Colin Pinney for laboratory assistance. This work was supported by Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico (CNPq) and National Science Foundation (NSF).
REFERENCES Andreux F, Cerri CC, Vose PB, Vitorello VA. 1990. Potential of stable isotopes 15N and 13C, methods for determining input and turnover in soils. In: Harrison P, Heal OW, Eds. Nutrient cycling in terrestrial ecosystems. Amsterdam: Elsevier. p 225– 75. 13
Balesdent JA, Mariotti A, Guillet B. 1987. Natural C abundance as a tracer for studies of soil organic matter dynamics. Soil Biol Biochem 19:25–30. Bastos TX, Diniz TD. 1982. Avaliac¸a˜o de clima do estado de Rondoˆnia para desenvolvimento Agrı´cola. Boletim de pesquisa No. 4, Bele´m: Embrapa-CPATU. 28 p. Bernoux M, Cerri CC, Neill C, Moraes JFL. 1998. The use of stable carbon isotopes for estimating soil organic matter turnover rates. Geoderma 82:43–58. Bonde TA, Christensen BT, Cerri CC. 1992. Dynamics of soil organic matter reflected by natural 13C abundance in particle size fractions of forested and cultivated Oxisols. Soil Biol Biochem 24:275–7. Boudot JP, Brahim BH, Chone´ T. 1988. Relative efficiency of complexed aluminium, noncrystalline Al hydroxide, alloplane and imogolite in retarding the biodegradation of citric acid. Geoderma 52:29–39. Boutton TW, Archer SR, Midwood AJ. 1999. Stable isotopes in ecosystem science: structure, function and dynamics of a subtropical savanna. Rapid Commun Mass Spectrom 13:1263–77. Brasil. 2004. Ministe´rio da Cieˆncia e Tecnologia. Comunicac¸a˜o Nacional Inicial do Brasil a Convenc¸a˜o-Quadro das Nac¸o˜es Unidas sobre Mudanc¸a do Clima. Brası´lia: Coordenac¸a˜o-Geral de Mudanc¸as Globais de Clima. p 74. Burke I, Kaye JP, Bird SP, Hall SA, McCulley RL, Sommerville GL. 2003. Evaluating and testing models of terrestrial biogeochemistry: the role of temperature in controlling decomposition. In: Canham C, Cole J, Laurenroth W, Eds. Models in ecosystem science. Princeton: Princeton University Press. p 225–53. Cerri CC, Balesdent J, Feller C, Victoria R, Plenecassagne A. 1985. Application du trac¸age isotopique natural en 13C a` l’e´tude de la dynamique de la matie`re organique dans les sols. C R Acad Sci Paris Serie II 300(9):423–8.
Cerri CC, Moraes JFL, Volkof B. 1992. Dinaˆmica do carbono orgaˆnico em solos vinculados a pastagens da Amazoˆnia Brasileira. Rev INIA Inv Agr 1(I):95–102. Cerri CEP, Paustian K, Bernoux M, Victoria RL, Mellilo J, Cerri CC. 2004. Modeling changes in soil organic matter in Amazon forest to pasture conversion with century model. Glob Change Biol 10:815–32. Cerri CEP, Easter M, Paustian K, Killian K, Coleman K, Bernoux M, Falloon P, Powlson DS, Batjes NH, Milne E, Cerri CC. 2007. Predicted soil organic carbon stocks and changes in the Brazilian Amazon between 2000 and 2030. Agric Ecosyst Environ 122:58–72. Chone´ T, Andreux F, Correa JC, Volkof B, Cerri CC. 1991. Changes in organic matter in an Oxisol from the Central Amazonian forest during eight years as pasture, determined by 13C isotopic comparison. In: Berthelin L, Ed. Diversity of environmental biogeochemistry. New York: Elsevier. p 391– 405. Conant RT, Drijber RA, Haddix ML, Parton WJ, Paul EA, Plante AF, Six J, Steinweg JM. 2007. Sensitivity of organic matter decomposition to warming varies with its quality. Glob Change Biol 14:868–77. Davidson EA, Artaxo P. 2004. Globally significant changes in biological processes of the Amazon Basin: results of the largescale biosphere–atmosphere experiment. Glob Change Biol 10:519–29. Davidson EA, Janssens IA. 2006. Temperature sensitivity of soil carbon decomposition and feedbacks to climate change. Nature 408:165–73. Denef K, Six J, Merckx R, Paustian K. 2004. Carbon sequestration in microaggregates of no-tillage soils with different clay mineralogy. Soil Sci Soc Am J 50:1935–44. Denef K, Zotarelli L, Boddey RM, Six J. 2007. Microaggregateassociated carbon as a diagnostic fraction for managementinduced changes in soil organic carbon in two Oxisols. Soil Biol Biochem 39:1165–72. Desjardins T, Andreux F, Volkof B, Cerri CC. 1994. Organic carbon and 13C contents in soils and soils size-fractions, and their changes due to deforestation and pasture installation in eastern Amazonia. Geoderma 61:103–18. Desjardins T, Barros E, Sarrazian M, Giardina C, Mariotti A. 2004. Effects of forest conversion to pasture on soil carbon content and dynamics in Brazilian Amazon. Agric Ecosyst Environ 103:365–73. Dick DP, Schwertmann U. 1996. Microaggregates from Oxisols and Inceptisols: dispersion through selective dissolutions and physicochemical treatments. Geoderma 74:49–63. Edwards AP, Bremner JM. 1967. Microaggregates in soils. J Soil Sci 18:64–73. Ehleringer JR, Buchmann N, Flanagan LB. 2000. Carbon isotope ratios in below ground carbon cycle processes. Ecol Appl 10:412–22. Elliott ET. 1986. Aggregate structure and carbon, nitrogen, and phosphorus in native and cultivated soils. Soil Sci Soc Am J 50:627–33. Fearnside PM, Barbosa RI. 1998. Soil carbon from conversion of forest to pasture in Brazilian Amazon. For Ecol Manag 108:147–66. Feigl BJ, Mellilo JM, Cerri CC. 1995. Changes in the origin and quality if soil organic matter after pasture introduction in Rondoˆnia (Brazil). Plant Soil 175:21–9.
Soil Carbon Turnover Measurement by Physical Fractionation Feller C, Beare MH. 1997. Physical control of soil organic matter dynamics in the tropics. Geoderma 79:69–119. Friedlingstein P, Cox P, Betts R, Bopp L, Von Bloh W, Brovkin V, Cadule P, Doney S, Eby M, Fung I, Bala G, John J, Jones C, Joos F, Kato T, Kawamiya M, Knorr W, Lindsay K, Mathews HD, Raddatz T, Rayner P, Reick C, Roeckner E, Schnitzler KG, Schnur R, Strassmann K, Weaver AJ, Yoshikawa C, Zeng N. 2006. Climate-carbon cycle feedback analysis: results from the (CMIP)-M-4 model intercomparison. J Clim 19:3337–53. Gearing JN. 1991. The study of diet and trophic relationships through natural abundance 13C. In: Coleman DC, Fry B, Eds. Carbon isotope techniques. San Diego: Academic press. p 201–18. Giardina CP, Ryan MG. 2000. Soil warming and organic carbon content—reply. Nature 408:790. Grac¸a PMLA, Fearnside PM, Cerri CC. 1999. Burning of Amazonian forest in Ariquemes, Rondoˆnia, Brazil: biomass, charcoal formation and burning efficiency. For Ecol Manag 120:179–91. Gullison R, Frumhoff PC, Canadell JG, Field CB, Nepstad DC, Hayhoe K, Avissar R, Curran LM, Friedlingstein P, Jones CD, Nobre C. 2007. Tropical forests and climate policy. Science 316:985–6. Institute SAS. 1990. SAS user’s guide. Statistics, Vol. 2. 6th edn. Cary, NC: SAS Inst. Jastrow J, Miller RM. 1997. Soil aggregate stabilization and carbon sequestration: feedbacks through organomineral associations. In: Lal R et al., Eds. Soil processes and the carbon cycle. Boca Raton: CRC Press. p 207–23. Kleber M, Sollins P, Sutton R. 2007. A conceptual model of organo-mineral interactions in soils: self-assembly of organic molecular fragments into zonal structures on mineral surfaces. Biogeochemistry 85:9–24. Krull ES, Skjemstad JO. 2003. d13C and d14N profiles in 14Cdated Oxisol and Vertisol as a function of soil chemistry. Geoderma 112:1–29. Lal R. 2004. Soil carbon sequestration to mitigate climate change. Geoderma 123:1–22. Lehmann J, Cravo MS, Zech W. 2001. Organic matter stabilization in a Xanthic Ferrasol of central Amazon as affected by single trees: chemical characterization of density, aggregate, and particle size fractions. Geoderma 99:147–68. Melillo JM, Borchers J, Chaney J, Fisher H, Fox S, Haxeltine A, Janetos A, Kicklighter DW, Kittel TGF, Mcguire AD, Mckeown
1221
R, Neilson R, Nemani R, Ojima DS, Painter T, Pan Y, Parton WJ, Pierce L, Pitelka L, Prentice C, Rizzo B, Rosenbloom NA, Running S, Schimel DS, Sitch S, Smith T, Woodward I. 1995. Vegetation ecosystem modeling and analysis project—comparing biogeography and biogeochemistry models in a continental-scale study of terrestrial ecosystem responses to climate-change and CO2 doubling. Global Biogeochem Cycles 9:407–37. Moraes JFL, Cerri CC, Mellilo JM. 1995. Soil carbon stocks of the Brazilian Amazon Basin. Soil Sci Soc Am J 59:244–7. Moraes JFL, Volkof B, Cerri CC, Bernoux M. 1996. Soil properties under Amazon forest change due to pasture installation in Rondoˆnia, Brazil. Geoderma 70:63–81. Neill C, Davidson EA. 2000. Soil carbon accumulation or loss following deforestation for pasture. In: Lal R, Kimble JM, Stewart BA, Eds. Global climate change and tropical ecosystems. Boca Raton: CRC Press. p 197–211. Neill C, Melillo JM, Steudler PA, Cerri CC, deMoraes JFL, Piccolo MC, Mrito M. 1997. Soil carbon and nitrogen stocks following forest clearing for pasture in the southwestern Brazilian Amazon. Ecol Appl 7:1216–25. O’Leary MH. 1981. Carbon isotope fractionation in plants. Phytochemistry 20:553–67. Oades JM. 1988. The retention of organic matter in soils. Biogeochemistry 5:35–70. Paul EA, Harris D, Collins HP, Schulthess U, Robertson GP. 1999. Evolution of CO2 and soil carbon dynamics in biologically managed, row-crop agroecosystems. Appl Soil Ecol 11:53–65. Six J, Conant RT, Paul EA, Paustian K. 2002. Stabilization mechanisms of soil organic matter: implications for C-saturation of soils. Plant Soil 241:155–76. Sørensen LH. 1972. Stabilization of newly formed amino-acid metabolites in soil by clay minerals. Soil Sci 114:5–11. Steudler PA, Mellilo JM, Feigl BJ, Neil C, Piccolo MC, Cerri CC. 1996. Consequence of forest-to-pasture conversion on CH4 fluxes in the Brazilian Amazon Basin. J Geophys Res 101:18547–54. Tisdall JM, Oades JM. 1982. Organic matter and water-stable aggregates in soils. J Soil Sci 33:141–63. Zotarelli L, Alves BJR, Urquiaga S, Boddey RM, Six J. 2007. Impact of tillage and crop rotation on light fraction and intraaggregate soil organic matter in two Oxisols. Soil Tillage Res 95:196–206.
