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Investigation:

TG-07 (Keller / Oliveira)

LBA Dataset ID:

TG07_ROOT_MORTALITY_LONGTERM

Originator(s):

1. SILVER, W.L.
2. THOMPSON, A.W.
3. MCGRODDY, M.E.
4. VARNER, R.K.
5. ROBERTSON, J.R.
      6. DIAS, J.D.
7. SILVA, H.S.
8. CRILL, P.M.
9. KELLER, M.M.

Point(s) of Contact:

ORNL DAAC User Services Office Oak Ridge National Laboratory Oak Ridge, Tennessee 37 (ornldaac@ornl.gov)

Dataset Abstract:

This data set reports the results of an experiment that tested the effects of root mortality on the soil-atmosphere fluxes of nitrous oxide, nitric oxide, methane, and carbon dioxide in a tropical evergreen forest over the course of one year. The study site in the Tapajos National Forest (TNF) is near km 83 on the Santarem-Cuiaba Highway south of Santarem, Para, Brazil. Root mortality was induced by isolating blocks of land to 1 m depth using trenching and root exclusion screening. Gas fluxes were measured weekly for ten weeks following the trenching treatment and monthly for the remainder of the year.

Beginning Date:

2000-05-31

Ending Date:

2001-07-14

Metadata Last Updated on:

2012-09-14

Data Status:

Archived

Access Constraints:

PUBLIC

Data Center URL:

http://daac.ornl.gov/

Distribution Contact(s):

ORNL DAAC User Services Office Oak Ridge National Laboratory Oak Ridge, Tennessee 37 (ornldaac@ornl.gov)

Access Instructions:

PUBLIC

Data Access:

IMPORTANT: The LBA-ECO Project website is no longer being supported. Links to external websites may be inactive. Final data products from the LBA project can be found at the ORNL DAAC. Please follow the fair use guidelines found in the dataset documentation when using or citing LBA data.
Datafile(s):

LBA-ECO TG-07 Long-Term Soil Gas Flux and Root Mortality, Tapajos National Forest :  http://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=1116

Documentation/Other Supporting Documents:

LBA-ECO TG-07 Long-Term Soil Gas Flux and Root Mortality, Tapajos National Forest :  http://daac.ornl.gov/LBA/guides/TG07_Root_Mortality_Longterm.html

Citation Information - Other Details:

Silver, W.L., A.W. Thompson, M.E. McGroddy, R.K. Varner, J.R. Robertson, J.D. Dias, H. Silva, P. Crill, and M.M. Keller. 2012. LBA-ECO TG-07 Long-Term Soil Gas Flux and Root Mortality, Tapajos National Forest. 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/1116

Keywords - Theme:

Parameter Topic Term Source Sensor
BIOMASS BIOSPHERE VEGETATION FIELD INVESTIGATION WEIGHING BALANCE
NITROGEN LAND SURFACE SOILS FIELD INVESTIGATION AUTOANALYZER
NITROUS OXIDE LAND SURFACE SOILS LABORATORY GC-FID (GAS CHROMATOGRAPH/FLAME IONIZATION DETECTOR)
SOIL BULK DENSITY LAND SURFACE SOILS FIELD INVESTIGATION WEIGHING BALANCE
SOIL GAS/AIR LAND SURFACE SOILS FIELD INVESTIGATION IR CO2 ANALYZER
SOIL MOISTURE/WATER CONTENT LAND SURFACE SOILS FIELD INVESTIGATION WEIGHING BALANCE

Uncontrolled Theme Keyword(s):  CARBON DIOXIDE, METHANE, NITRIC OXIDE, NITROUS OXIDE, ROOT DECOMPOSITION, ROOT PRODUCTIVITY, ROOT RESPIRATION, ROOT TURNOVER

Keywords - Place (with associated coordinates):

Region
(click to view profile)
Site
(click to view profile)
North South East West
Pará Western (Santarém) km 83 Logged Forest Tower Site -3.01700 -3.01700 -54.97070 -54.97070

Related Publication(s):

Silver, W. L., A. W. Thompson, M. E. McGroddy, R. K. Varner, J. R. Robertson, J. D. Dias, H. Silva, P. Crill, and M. Keller. 2005. Fine roots dynamics and trace gas fluxes in two lowland tropical forest soils. Global Change Biology 11: 290-306.

Data Characteristics (Entity and Attribute Overview):

Data Characteristics:

Data are presented in five comma-delimited ASCII files. The data files are organized as follows:



<pre>

File #1:

File name: TG07_trench_plot_gas_fluxes.csv



Column Column Variable description

# heading

1 Date Date (yyyy-mm-dd)

2 Day_year Day of the year January 1=1 and December 31=365

3 Day_expt Day since the start of the experiment

4 Soil_type Soil texture class: Soil or Clay. See documentation for more detail on soils.

5 Treatment Plot treatment: Control or Trench (indicating trenched to 1.5 meters depth)

6 Plot Plot identification number: 1 - 5

7 Rep Replicate within the plot: A or B

8 Flux_N2O Flux of nitric oxide reported in ng N per centimeter squared per hour (ng/cm2/hr): positive values indicate a flux from the soil to the atmosphere and negative values indicate a flux from the atmosphere into the soil

9 Flux_CH4 Flux of methane reported in mg CH4 per meter squared per day (mg/m2/day): positive values indicate a flux from the soil to the atmosphere and negative values indicate a flux from the atmosphere into the soil

10 Time Start of sampling time (hh:mm) for NO and CO2 in local time ( GMT+3)

11 T_air Air temperature measured at 30 cm above the ground in degrees Centigrade

12 T_soil Soil temperature taken at 2 cm depth in degrees Centigrade

13 Flux_NO Flux of nitrous oxide measured in nanograms of nitrogen in the form of NO per centimeter squared of soil surface per hour (ng N per cm2 per hr or ng/cm2/hr). Positive values indicate a flux from the soil to the atmosphere.

14 Flux_CO2 Flux of carbon dioxide measured in micromoles of carbon dioxide per meter squared of soil surface per second (umoles CO2 per m2 per s or umoles/m2/sec). Positive values indicate a flux from the soil to the atmosphere.



Example records from File #1: TG07_trench_plot_gas_fluxes.csv

Date,Day_year,Day_expt,Soil_type,Treatment,Plot,Rep,Flux_N2O,Flux_CH4,Time,T_air,T_soil,Flux_NO,Flux_CO2

2000-06-04,156,1,Clay,Control,1,A,31.39,2.8,12:41,26.7,25,0.7,3.43

2000-06-04,156,1,Clay,Control,1,B,14.87,-0.49,12:46,26.9,25.2,1.21,6.18

2000-06-04,156,1,Clay,Control,2,A,10.53,-0.43,10:27,26.5,24.7,8.42,3.85

2000-06-04,156,1,Clay,Control,2,B,4.68,-0.78,10:33,26.4,25,10.44,3.28

2000-06-04,156,1,Clay,Control,3,A,1.77,-9999,11:05,27.3,24.9,0.76,3.33

2000-06-04,156,1,Clay,Control,3,B,14.5,-0.97,11:17,26.7,24.9,1.33,4.44

2000-06-04,156,1,Clay,Control,4,A,16.33,-0.03,10:12,26.5,24.9,0.66,3.71

2000-06-04,156,1,Clay,Control,4,B,37.06,-0.32,10:18,26.2,24.1,0.83,3.51

2000-06-04,156,1,Clay,Control,5,A,16.59,-0.33,11:36,26.4,24.8,0.5,3.73

2000-06-04,156,1,Clay,Control,5,B,7.55,-0.67,11:42,26.5,24.8,0.81,4.78

2000-06-04,156,1,Clay,Trench,1,A,8.87,0.69,12:30,26.7,25,5.58,1.69



File #2:

File name: TG07_trench_plot_root_mass.csv



Column Column heading Variable description

1 Date Sampling date (yyyy-mm-dd)

2 Soil_type Soil texture class: Soil or Clay. See documentation for more detail on soils.

3 Treatment Plot treatment: Control or Trench (indicating trenched to 1.5 meters depth)

4 Plot Plot identification number: 1 - 5

5 Rep Replicate number: there were three replicate samples per plot per sample date

6 Mass_live_rts Mass of live fine roots measured after oven drying at 60 degrees C reported in grams (g)

7 Mass_dead_rts Mass of dead fine roots measured after oven drying at 60 degrees C reported in grams (g)

8 Mass_medium_rts Mass of roots with diameters greater than 2 and less than or equal to 5 mm measured after oven drying at 60 degrees C reported in grams (g)

9 Mass_coarse_rts Mass of roots with diameters greater than 5 mm measured after oven drying at 60 degrees C reported in grams (g)

10 Density_live_rts Density of live fine roots calculated by dividing the measured mass of live fine roots by the volume of the sampling cylinder, expressed as grams per meter squared (g/m2)

11 Density_dead_rts Density of dead fine roots calculated by dividing the measured mass of dead fine roots by the volume of the sampling cylinder, expressed as grams per meter squared (g/m2)



Example records from File #2: TG07_trench_plot_root_mass.csv

Date,Soil_type,Treatment,Plot,Rep,Mass_live_rts ,Mass_dead_rts,Mass_medium_rts,Mass_coarse_rts,Density_live_rts ,Density_dead_rts

2000-06-04,Clay,Control,1,1,0.1022,0.6077,0.0789,0,36.15,214.96

2000-06-04,Clay,Control,1,2,0.1486,0.3664,0.0304,0,52.56,129.61

2000-06-04,Clay,Control,1,3,0.068,0.5625,0.238,0,24.05,198.97

2000-06-04,Clay,Control,2,1,0.021,0.2027,0.3003,0.1141,7.43,71.7

2000-06-04,Clay,Control,2,2,0.0332,0.8438,0.1206,1.1709,11.74,298.48

2000-06-04,Clay,Control,2,3,0.0431,0.198,0.3487,0.6135,15.25,70.04

2000-06-04,Clay,Control,3,1,0.2198,0.606,0.5935,0.3141,77.75,214.36

2000-06-04,Clay,Control,3,2,0.0439,0.3007,0.2199,0,15.53,106.37

2000-06-04,Clay,Control,3,3,0.1105,0.2515,0,0,39.09,88.96

2000-06-04,Clay,Control,4,1,0.069,0.4609,0.3594,0,24.41,163.04



File #3:

File name: TG07_trench_plot_root_chemistry.csv



Column Column heading Variable description

1 Date Sampling date (yyyy-mm-dd)

2 Soil Soil texture class: Soil or Clay. See documentation for more detail on soils.

3 Treatment Plot treatment: Control (none included in this data file) or Trench (indicating trenched to 1.5 meters depth).

4 Plot Plot identification number: 1 - 5

5 Rt_mass_remaining Oven dried root mass expressed as a percent of the mean fine root mass measured at the onset of the treatment

6 Ash Percent of root mass composed of inorganic compounds determined by ashing samples at 550 degrees C

7 Non_polar_ext Percent of root carbon composed of compounds extractable in non-polar solutions

8 Water_sol_C Percent of root carbon composed of compounds extractable in water

9 Acid_sol_C Percent of root carbon composed of compounds extractable in acid solutions

10 Tannins Percent of root carbon composed of tannins

11 Water_sol_glu Water soluble carbon from roots expressed as glucose equivalents

12 Acid_sol_glu Acid soluble carbon from roots expressed as glucose equivalents

13 Lignin Root lignin content calculated as the difference between total sample mass and the sum of the 3 extractable fractions

14 Carbon Total root carbon content measured by combustion expressed as percent of total mass

15 Nitrogen Total root nitrogen content measured by combustion expressed as percent of total mass

16 C_to_N Carbon to nitrogen ratio of root tissue calculated on mass basis

17 Lignin_to_N Lignin to nitrogen ratio of root tissue calculated on a mass basis



Example records from File #3: TG07_trench_plot_root_chemistry.csv

Date,Soil,Treatment,Plot,Rt_mass_remaining,Ash,Non_polar_ext_C,Water_sol_C,Acid_sol_C,Tannins,Water_sol_glu,Acid_sol_glu,Lignin,Carbon,Nitrogen,C_to_N,Lignin_to_N

2000-06-04,Clay,Trench,1,1,6.59,3.94,6.19,50.4,1.41,0.98,29.42,39.46,50.32,1.55,32.46,25.46

2000-06-04,Clay,Trench,2,1,7.84,2.05,5.34,52.08,0.69,1.15,31.38,40.53,49.72,1.27,39.15,31.91

2000-06-04,Clay,Trench,3,1,6.93,7.67,5.88,45.92,1.14,0.9,28.69,40.54,52.28,1.5,34.85,27.03

2000-06-04,Clay,Trench,4,1,7.61,5.39,6.7,53.01,1.21,1.09,29.64,34.9,50.91,1.54,33.06,22.66

2000-06-04,Clay,Trench,5,1,8.32,4.99,7.64,55.85,1.63,1.16,33.68,31.52,48.87,1.42,34.42,22.2

2000-06-04,Sand,Trench,1,1,5.64,2.7,8.66,48.5,1.3,1.36,24.8,40.13,51.5,1.79,28.77,22.42

2000-06-04,Sand,Trench,2,1,7.95,2.43,6.19,43.24,1.23,1.16,19.67,48.15,50.75,1.38,36.78,34.89

2000-06-04,Sand,Trench,3,1,7.23,2.32,6.53,54.82,1,1.52,30.28,36.33,50.05,1.19,42.06,30.53



File #4

File name: TG07_trench_plot_soil_N.csv



Column Column heading Variable description

1 Date Sampling date (yyyy-mm-dd)

2 Soil_type Soil texture class: Soil or Clay. See documentation for more detail on soils.

3 Treatment Plot treatment: Control or Trench (indicating trenched to 1.5 meters depth)

4 Plot Plot identification number: 1 - 5

5 Rep Replicate number: there were three replicate samples per plot per sample date

6 Soil_moisture Soil moisture reported in percent by weight

7 Soil_NH4_initial Initial concentration of NH4-N extracted from the soil with 2M KCl reported in micrograms of N in the form of NH4 per gram dry weight of soil (ug N/gdw)

8 Soil_NO3_initial Initial concentration of NO3-N extracted from the soil with 2M KCl reported in micrograms of N in the form of NO3 per gram dry weight of soil (ug N/gdw)

9 Soil_NH4_final Final concentration of NH4-N extracted from the soil with 2M KCl reported in micrograms of N in the form of NH4 per gram dry weight of soil (ug N/gdw)

10 Soil_NO3_final Final concentration of NO3-N extracted from the soil with 2M KCl reported in micrograms of N in the form of NO3 per gram dry weight of soil (ug N/gdw)

11 Net_mineralization Calculated rate of net mineralization of N reported in micrograms of N per gram dry weight of soil per day (ug/gdw/day)

12 Net_nitrification Calculated rate of net nitrification reported in micrograms of N per gram dry weight of soil per day (ug/gdw/day)



Missing data is indicated by -9999



Example records from File #4: TG07_trench_plot_soil_N.csv

Date,Soil_type,Treatment,Plot,Rep,Soil_moisture,Soil_NH4_initial,Soil_NO3_initial ,Soil_NH4_final ,Soil_NO3_final,Net_mineralization,Net_nitrification

2000-06-04,Clay,Control,1,1,27.35,0.56,10.95,7.63,28.81,1.01,2.55

2000-06-04,Clay,Control,1,2,31.77,27.18,29.68,2.44,36.64,-3.53,0.99

2000-06-04,Clay,Control,1,3,32.58,1.69,12.61,4.35,70.36,0.38,8.25

2000-06-04,Clay,Control,2,1,32.4,1.45,15.94,1.34,38.73,-0.02,3.26

2000-06-04,Clay,Control,2,2,28.69,2.15,13.28,0.94,46.74,-0.17,4.78

2000-06-04,Clay,Control,2,3,34.07,0.7,17.43,2.49,45.18,0.26,3.96

2000-06-04,Clay,Control,3,1,28.32,1.22,15.84,1.77,37.03,0.08,3.03

2000-06-04,Clay,Control,3,2,28.59,4.8,21.93,6.41,45.83,0.23,3.41

2000-06-04,Clay,Control,3,3,27.1,18.45,21.67,5.17,51.13,-1.9,4.21

2000-06-04,Clay,Control,4,1,31.68,1.62,13.62,17.68,46.35,2.29,4.68

2000-06-04,Clay,Control,4,2,29.9,0.79,7.82,0.3,21.94,-0.07,2.02

2000-06-04,Clay,Control,4,3,29,4.42,11.23,5,59.22,0.08,6.86



File #5

File name: TG07_trench_plot_soil_moisture.csv



Column Column heading Variable description

1 Date Sampling date (yyyy-mm-dd)

2 Soil_type Soil texture class: Soil or Clay. See documentation for more detail on soils.

3 Treatment Plot treatment: Control or Trench (indicating trenched to 1.5 meters depth)

4 Plot Plot identification number: 1 - 5

5 Soil_moisture Gravimetric soil moisture calculated after drying the soil sample at 110 degrees C, expressed as percent (%)

6 WFPS Water filled pore space calculated from the soil moisture and soil texture measurements



Missing data are represented by -9999



Example records from File #5: TG07_trench_plot_soil_moisture.csv

Date,Soil_type,Treatment,Plot,Soil_moisture,WFPS

2000-05-31,Clay,Control,1,43.53,0.72

2000-05-31,Clay,Control,2,40.99,0.67

2000-05-31,Clay,Control,3,35.53,0.58

2000-05-31,Clay,Control,4,39.75,0.65

2000-05-31,Clay,Control,5,40.34,0.66

2000-05-31,Clay,Trench,1,44.6,0.73

2000-05-31,Clay,Trench,2,34.32,0.56

2000-05-31,Clay,Trench,3,46.72,0.77

2000-05-31,Clay,Trench,4,41.12,0.68

2000-05-31,Clay,Trench,5,37.21,0.61

2000-06-04,Clay,Control,1,44.17,0.73

2000-06-04,Clay,Control,2,46.61,0.77

2000-06-04,Clay,Control,3,38.9,0.64



</pre>

Data Application and Derivation:

From these measurements estimates of the decomposition rate of roots as well as the contribution of roots to soil-atmosphere gas exchange can be made.

Quality Assessment (Data Quality Attribute Accuracy Report):

Quality Assessment:

NO standards were run in the field at the beginning and end of 8 enclosure flux samples or approximately every hour. NO standard response calculated using a linear fit of the two standards encompassing the measurement period was compared to the frequent (generally hourly) standardization. A given hourly standard run varied by as much as 60% from the standard response calculated from the linear fit. On two dates of eight tested, at least 50% of the standards fall outside of the predicted standard response by at least 20% based on the starting and ending standards. On two other dates at least 10% of the standard runs fall outside of this +/-20% window. For additional QA, please see flux measurement section below.

Process Description:

Data Acquisition Materials and Methods:

Site Description

The region receives approximately 2000 mm of precipitation per year and has an annual mean temperature of 25 C [Silver et al., 2000]. Vegetation at the site is evergreen, mature tropical forest with a total biomass of about 372 Mg ha-1 [Keller et al., 2001]. Experimental plots were located on contrasting soils, a clay textured Oxisol (80% clay, 18% sand, 2% silt) and a sand textured Ultisol (60% sand, 38% clay, 2% silt) [Silver et al., 2000].



Experimental Design

The experiment was a randomized complete block design (Varner et al., 2003). For each soil type, 5 pairs of 2.5 x 2.5 m plots were located so that there were no trees greater than 10 cm diameter at breast height (DBH; 1.3 m) on the plots. One plot in each pair was randomly selected for trenching. In the trenched plots, trenches were dug to 1-m depth and were lined with a fine stainless steel mesh (<0.5 mm) to prevent the penetration of roots while allowing the movement of water and gases. All vegetation was clipped from the trenched plots at the time of trenching and every two weeks thereafter to prevent colonization of the plot by live roots. The trenching operations were completed in the period from Julian day 147 through 156 in 2000 (May 27 through June 4). For all plots, measurements were made in an interior square region, 2 x 2 m that was surrounded by a 0.5-m wide buffer strip.



Trace Gas Flux Measurements

The soil-atmosphere fluxes of CO2, NO, N2O and CH4 were measured weekly for approximately 10 weeks following the trenching treatment and N2O and CH4 wee measured monthly after that until July 2001. After the weekly sampling ended CO2 and NO were measured monthly at these plots for 5 months and then every 2.5 months through May 2001. Two chamber bases were inserted approximately 2 cm depth in the soil at randomly selected points in the sampled plots within 30 minutes of the weekly flux measurement. These chamber bases were removed immediately after flux measurements were completed. Dynamic flow-through chambers were used for measurement of NO and CO2 and static vented chambers were used for measurements of N2O and CH4 [Keller and Reiners, 1994]. The measurement of these two pairs of gases was sequential after lifting the chamber top to equilibrate the headspace with ambient air.



An integrated backpack system was used to measure NO and CO2 over 3 to 10 minutes from enclosures. The flow through the chamber was regulated to about 300 cm3 min-1. Air entered the chamber through a chimney-like air-gap that was specifically designed to minimize exchange with the outside air and to avoid pressure fluctuations within the chamber.

Air flowed from the soil enclosure through a Teflon-lined polyethylene sample line 30 m in length and then it entered an infrared gas analyzer (Li-Cor 6262) for CO2 measurement. From the Li-6262, the sampled air then passed through a flow control manifold where it was mixed with a make-up air flow of about 1200 cm3 min-1 and a flow of NO (1 ppm) standard gas that varied from 3 to 10 cm3 min-1 as measured on an electronic mass flowmeter (Sierra Top-Trak). The make-up air and standard addition maintain optimum and linear performance of the NO2 chemiluminescent analyzer (Scintrex LMA-3). The mixed sample stream passed through a Cr2O3 catalyst for conversion of NO to NO2 [Levaggi et al., 1974]. The NO2 chemiluminescent analyzer was standardized by a two-point calibration approximately hourly. The intra-day stability of the calibration on each sampling date was checked by comparison of each standard run to a linear interpolation between the standards runs at the beginning and end of the daily measurement period. The concentration of the field NO standard was compared periodically with laboratory standards to assure that they did not drift [Veldkamp and Keller, 1997]. Signals from the CO2 and NO2 analyzers and the mass flow meter for the NO standard gas were recorded on a datalogger (Campbell CR10). Fluxes were calculated from the linear increase of concentration versus time.



Static enclosure measurements were made for CH4 and N2O fluxes using the same bases and vented caps [Keller and Reiners, 1994]. Four enclosure headspace samples were taken over a 30-minute sampling period with 20-ml nylon syringes. Analysis of grab samples for CH4 and N2O were completed within 36 hours by FID and ECD gas chromatography. Gas concentrations were calculated by comparing peak areas for samples to those for standards.





Root biomass

Roots were sampled using a root corer with a 6-cm internal diameter [Vogt and Persson, 1991]. Roots were sorted and dried at 65 degree C and weighed.



Root chemistry

Root C chemistry was measured using sequential extractions (Ryan et al., 1989) at the Center for Water and the Environment of the Natural Resources Research

Institute, University of Minnesota, Duluth, MN. One bulked root sample was used per plot and date. The C fractions measured were nonpolar extractives, water soluble and acid soluble extracts, tannins, and water and acid soluble fractions expressed as glucose equivalents. Lignin was determined as the difference between the whole sample and the sum of the nonpolar extractives, and water and acid soluble fractions. Total C and N were measured on a CN analyzer (CE Elantec, Lakewood, NJ, USA) at UC Berkeley. All root data are

expressed on an oven dry equivalent, ash-free basis.



Soil moisture and N pools and fluxes

For this study, we measured gravimetric soil moisture, soil temperature, soil N pools, and net N mineralization and nitrification rates from trench plots

and controls. Soil moisture was sampled in close proximity to the surface flux chambers using three 2.5cm diameter by 10cm deep soil cores. Samples were collected during 15 dates (all but four of the trace gas sampling periods). Soils were dried at 105 degrees C until reaching a constant weight and then weighed to determine moisture loss. Water-filled pore space (WFPS) was estimated from soil moisture and porosity (porosity x bulk density/particle density)for trench plots and controls. Bulk density values were

taken from Silver et al. (2000) and particle density was assumed to be 2.65 g cm-3. Soil N pools were determined on fresh samples (0 to 10cm depth) during the five dates that we sampled the trench plots for root biomass. We took three replicate samples per plot with a 2.5cm diameter corer to 10cm depth (n= 20 plots and 60 samples per time period). Soils were extracted with 2M

KCl the same day of collection. Soil extract N concentrations were determined at U.C. Berkeley on a Lachat QC 8000 autoanalyzer (Lachat Instruments,

Loveland, CO, USA). Net N mineralization and nitrification rates were estimated for the first three measurement periods according to Hart et al. (1994).

References:

Hart SC, Stark JM, Davidson EA et al. (1994) Nitrogen mineralization, immobilization, and nitrification. In: Methods of Soil Analysis, Part 2. Microbiological and Biochemical Properties(ed.Weaver RW pp. 985-1018. Soil Science Society of America, Madison.



Keller, M., et al., (2001) Biomass in the Tapajos National Forest, Brazil: Examination of sampling and allometric uncertainties, Forest Ecol. Manage., 154, 371-382. doi:10.1016/S0378-1127(01)00509-6



Keller, M., and W. A. Reiners, (1994). Soil-atmosphere exchange of nitrous oxide, nitric oxide, and methane under secondary succession of pasture to forest in the Atlantic lowlands of Costa Rica, Global Biogeochem. Cycles, 8, 399-410. doi:10.1029/94GB01660



Levaggi, D., et al., (1974). Quantitative analysis of nitric oxide in presence of nitrogen dioxide at atmospheric concentrations, Environ. Sci. Tech., 8, 348-350. doi:10.1021/es60089a003



Ryan MG, Melillo JM, Ricca A (1989) A comparison of methods for determining proximate carbon fractions of forest litter. Canadian Journal of Forest Research, 20, 166�171.



Silver, W. L., et al., (2000). Effects of soil texture on belowground carbon and nutrient storage in a lowland Amazonian forest ecosystem, Ecosystems, 3, 193-209. doi:10.1007/s100210000019



Varner, R.K., M. Keller, J.R. Robertson, J.D. Dias, H. Silva, P.M. Crill, M. McGroddy and W.L. Silver, (2003). Experimentally induced root mortality increased nitrous oxide emission from tropical forest soils, Geophys. Res. Letts., 30, 10.1029/2002GL016164.



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