Revision date: August 15, 2011

Summary:

This data set contains carbon isotope signatures from soil organic matter collected from the following sites: the forests of the ZF-2 INPA reserve approximately 80 km north of the city of Manaus, Amazon; the Tapajos National Forest approximately 83 km south of the city of Santarem, Para; and the Fazenda Vitoria, a ranch near the city of Paragominas, Para. Samples from the Fazenda Vitoria were from degraded and managed pasture sites as well as mature and secondary forests. In addition, carbon isotope signatures from roots sorted by size class, hand-picked from soil pits in the Flona Tapajos and Fazenda Vitoria, are included, as are carbon isotope signatures from soil gases from samples collected at the Fazenda Vitoria. There are 4 ASCII data files with this data set.

Data Citation:

Cite this data set as follows:

Telles E.D.C., P.B. de Camargo, L.A. Martinelli, S.E. Trumbore, E.S. da Costa, J. Santos, N. Higuchi, R.C. Oliveira and D. Markewitz. 2011. LBA-ECO CD-08 Carbon Isotopes in Belowground Carbon Pools, Amazonas and Para, Brazil. Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. http://dx.doi.org/10.3334/ORNLDAAC/1025

Implementation of the LBA Data and Publication Policy by Data Users:

The LBA Data and Publication Policy [http://daac.ornl.gov/LBA/lba_data_policy.html] is in effect for a period of five (5) years from the date of archiving and should be followed by data users who have obtained LBA data sets from the ORNL DAAC. Users who download LBA data in the five years after data have been archived must contact the investigators who collected the data, per provisions 6 and 7 in the Policy.

This data set was archived in August of 2011. Users who download the data between August 2011 and July 2016 must comply with the LBA Data and Publication Policy.

Data users should use the Investigator contact information in this document to communicate with the data provider. Alternatively, the LBA Web Site [http://lba.inpa.gov.br/lba/] in Brazil will have current contact information.

Data users should use the Data Set Citation and other applicable references provided in this document to acknowledge use of the data.

Table of Contents:

• 1 Data Set Overview
• 2 Data Characteristics
• 3 Applications and Derivation
• 4 Quality Assessment
• 5 Acquisition Materials and Methods
• 6 Data Access
• 7 References

1. Data Set Overview:

Project: LBA(Large-Scale Biosphere-Atmosphere Experiment in the Amazon)

Activity: LBA-ECO

LBA Science Component: Carbon Dynamics

Team ID: CD-08 (Trumbore/ Camargo)

The investigators were Trumbore, Susan E.;Camargo, Plinio B. de ; Chambers, Jeffrey Q.; Costa, Enir Salazar da; Martinelli, Luiz Antonio; Perez Acosta, Tibisay Josefina; Southon, John R.; Telles, Everaldo de Carvalho Conceicao and Vieira, Simone Aparecida . You may contact Trumbore, Susan (setrumbo@uci.edu)

LBA Data Set Inventory ID: CD08_C_Isotopes_Belowground

Tropical forests play a key role in controlling the global carbon balance holding 26% of the carbon (C) stored globally in soil organic matter (SOM). Average residence time of C in these ecosystems is predicted to be less than that of other biomes such as boreal forests. Eddy flux measurements at various locations have suggested that tropical forests may act as important sinks of C though these findings are highly debated. Belowground carbon pools in tropical forests may be important to the role of these ecosystems as sinks or sources of C but our knowledge of their dynamics is limited. Two factors are key to understanding the potential for SOM to behave as a source or sink of CO2: the size and direction of the soil pool C flux and the residence time of C in this pool. Here we present data on belowground C pools from two lowland tropical forests in Amazonia. By measuring C pools in SOM and fine root pools as well as the radiocarbon signatures of each we use a model to predict the capacity of each soil to act as a sink for C.

2. Data Characteristics:

Data are presented in four ASCII comma-delimited (.csv) files:
File 1: C_isotopes_roots_and_SOM_Tapajos_and_Manaus.csv
File 2: C_isotopes_SOM_Paragominas_1996.csv
File 3: C_isotopes_roots_Paragominas.csv
File 4: C_isotopes_soil_CO2_Paragominas.csv

File #1: C_isotopes_roots_and_SOM_Tapajos_and_Manaus.csv

Example data records

File #2: C_isotopes_SOM_Paragominas_1996.csv

Example data records

File #3: C_isotopes_roots_Paragominas.csv

Example data records

File #4: C_isotopes_soil_CO2_Paragominas.csv

Example data records

Site boundaries: (All latitude and longitude given in decimal degrees)

Time period:

• The data set covers the period 1992/05/01 to 1999/07/05.
• Temporal Resolution: Annual

Platform/Sensor/Parameters measured include:

• LABORATORY / CHN ANALYZER / CARBON
• LABORATORY / MASS SPECTROMETER / SOIL GAS/AIR
• LABORATORY / MASS SPECTROMETER / CARBON
• LABORATORY / MASS SPECTROMETER /ISOTOPES

3. Data Application and Derivation:

Understanding the dynamics of the soil C pools requires an accurate measurement of the size of the pools and the fluxes in and out of each pool as well as the residence time of C in each. The rate of incorporation of nuclear weapons testing 14C into the soil C reservoir provides a useful tool for deciphering C turnover in soils on timescales of decades to hundreds of years. Using the radiocarbon signature of the current atmosphere and steady state assumptions, the decomposition rate of each C pool can be determined. There are few data on the age of C in the fine root pool in tropical forests. Surface litter inputs into the soil C pools generally reflect the atmospheric radiocarbon signature of the current year, however, for roots the average time elapsed since the material from which it was constructed was fixed from the atmosphere by photosynthesis may vary significantly.

4. Quality Assessment:

The data have been reviewed and there are no known problems with them.

Radiocarbon data are reported in delta notation (per mil deviation from 95% of the 14C/12C ratio of oxalic acid I standard, decay corrected to 1950). All samples have been corrected for mass-dependent fractionation of 14C using the 13C data.

The analytical uncertainty associated with these radiocarbon analyses is plus/minus 5 per mil based on repeated determinations of secondary standards. The Delta 14C data were measured in the year of sampling.

The precision of 13C analysis was plus/minus 0.1 per mil.

5. Data Acquisition Materials and Methods:

Data were collected from the following sites: ZF-2 INPA reserve approximately 80 km north of the city of Manaus, Amazon; the Tapajos National Forest approximately 83 km south of the city of Santarem, Para; and  the Fazenda Vitoria, a ranch near the city of Paragominas, Para.

The Manaus site is characterized by kaolinite clay rich Oxisols on the plateaus, and intermittently flooded, sandy textured soils (Spodosols) in the lowland sites along the small streams that dissect the plateau areas. At the Tapajos site there are similar clay rich Oxisol dominated plateaus and sandier (Oxisols) soils in local depressions though these soils are well drained unlike what is found in Manaus. 

The Fazenda Vitoria site is a ranch in Paragominas with pasture sites, secondary and mature forests. This site experiences seasonal drought with less than 250 mm of the total annual precipitation of 1,750 mm falling between June and November. Despite the extended dry season, the forests in this region are evergreen. To compare soil carbon cycling in pastures and forests, study plots were set up in 3 mature forest sites, 2 degraded pasture sites and 2 managed pasture sites. The degraded pasture site was originally cleared in 1969, planted with Panicum maximum and later Brachiaria humidicola, and has been heavily grazed to the present. Woody shrubs and treelets now dominate the site and it supports little grazing. The managed pasture shared a similar land use history until 1987 when it was disk-harrowed, fertilized with phosphorus, and reseeded with a more productive C4 grass. It currently has no woody shrubs.

Soil sample collections:
Soil samples were collected from all sites. Sixteen soil profiles in each of the four soil types were sampled to a depth of 50 cm for C stocks. Three pits for each soil were sampled to 2 m depth. Samples from one representative 2 m pit were analyzed for radiocarbon and stable isotopes and these data are presented here. In addition to soil samples, bulk charcoal samples were separated from soil and run for radiocarbon and stable isotopes using the same methodology.

Root sample collections:
Fine root samples were collected in 1999 from deep soil pits in a sandy loam soil at the km 83 site within the Tapajos National Forest (Telles et al., 2003). Roots were not separated into live and dead categories. Soil cores were subsampled for fine roots at 0-10, 40-60, 135-155, 285-305 cm depth intervals, using the same methods by which fine roots were sampled in Paragominas between 1993 and 1996.

Soil sample preparation and analysis:
Soil samples were sieved to less than 2 mm diameter and homogenized. Fine roots and charcoal were removed and the soils were ground for analysis. Gravimetric C content and C stable isotopic composition, expressed as delta 13C, were measured using an elemental analyzer coupled to a continuous flow stable isotope ratio mass spectrometer at the USP CENA campus in Piracicaba, Sao Paulo state. Samples for radiocarbon analysis were sealed in evacuated quartz tubes with cupric oxide wire and combusted at 900 degrees C for 2 hours. Evolved CO2 was purified cryogenically and then reduced to graphite by the zinc reduction method (Vogel 1992) for analysis accelerator mass spectrometry at the Center for AMS at the Lawrence Livermore National Laboratory, Livermore CA or at the WM Keck Carbon Cycle AMS facility at UC Irvine.

Root sample preparation and analysis:
Roots were separated from bulk soil by flotation (Nepstad et al., 1994) and separated into two size fractions (less than 1 mm and between one and 2 mm diameter). For the samples from the clay Oxisol live and dead fine root pools were separated by hand using texture and color criteria to distinguish roots. Separated roots were weighed and then stored in alcohol. Samples for radiocarbon were pretreated following Gaudinski et al. (2001). Fine roots were washed sequentially in 1 N HCl, 1N NaOH and 1N HCl with distilled water rinses after each step. Pretreated samples were then oven dried at 60 degrees C and ground. Ground root tissue was combusted in quartz tubes with cupric oxide wire and combusted at 900 degrees C for 2 hours. Evolved CO2 was purified cryogenically, subsampled for 13C analysis and then reduced to graphite by the zinc reduction method (Vogel 1992) for analysis by accelerated mass spectrometry at the Center for AMS at the Lawrence Livermore National Laboratory, Livermore CA. Stable C isotopes were measured using dual inlet isotope ratio mass spectrometry in the CENA laboratory.

Soil gas sample collection:
Soil gases were collected from stainless steel tubes perforated at one end and installed into the walls of soil pits, as described in Davidson and Trumbore (1995). Tubes were capped with septa and syringes were used to draw ~10 ml samples for concentration measurements. For isotope samples, tubes were either connected to pre-evacuated 500 cc steel canisters (for depths up to 100 cm) or 60 cc syringe samples were used to fill serum vials sealed with butyl rubber septa (for depths >100 cm). Samples were transported to the isotope laboratory at CENA for purification of CO2 and preparation of graphite and AMS measurement as above.

6. Data Access:

This data is available through the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Data Archive Center:

Contact for Data Center Access Information:
E-mail: uso@daac.ornl.gov
Telephone: +1 (865) 241-3952

7. References:

Davidson, E.A. and S.E. Trumbore. 1995. Gas diffusivity and production of CO2 in deep soils of the eastern Amazon, Tellus Series B-Chemical and Physical Meteorology 47B(5): 550-565.

Gaudinski, J.B., S.E. Trumbore, E.A. Davidson, A.C. Cook, S. Markewitz and D.D. Richter. 2001. The age of fine-root carbon in three forest of the eastern United States measured by radiocarbon. Oecologia 129: 420-429

Nepstad, D.C., C.R. Decarvalho, E.A. Davidson et al. 1994. The role of c: 666-669.

Stuiver, M. and Polach, H.A. 1977. Discussion: Reporting of 14C Data.  Radiocarbon 19(3), 1977, p. 355–363.

Telles, E.D.C., P.B. de Camargo, L.A. Martinelli, S.E. Trumbore, E.S. da Costa, J. Santos, N. Higuchi, and R.C. Oliveira. 2003. Influence of soil texture on carbon dynamics and storage potential in tropical forest soils of Amazonia. Global Biogeochemical Cycles 17(2):1040, 2003 May 2.

Vogel, J.S. 1992. A rapid method for preparation of biomedical targets for AMS. Radiocarbon 34: 344-350.

Related Publications

• Trumbore, S., E.S. da Costa, D.C. Nepstad, P.B. de Camargo, L.I.Z.A. Martinelli, D. Ray, T. Restom, and W. Silver. 2006. Dynamics of fine root carbon in Amazonian tropical ecosystems and the contribution of roots to soil respiration. Global Change Biology 12(2):217-229.
• Brando P.M., D.C. Nepstad, E. A. Davidson, S. E. Trumbore,D. Ray and P. Camargo. 2008. Drought effects on litterfall, wood production and belowground carbon cycling in an Amazon forest: results of a throughfall reduction experiment. Phil. Trans. Royal Society B, 363(1498): 1839-1848.
• de Camargo, P.B., S.E. Trumbore, L.A. Martinelli, E.A. Davidson, D.C. Nepstad, and R.L. Victoria. (1999) Soil carbon dynamics in regrowing forest of eastern Amazonia. Global Change Biology 5(6):693-702