Nitrous oxide emission and isotopic composition data from four dryland sites in Southern California

Metadata:
Identification_Information:
Citation:
Citation_Information:
Originator: Krichels, Alexander H.
Originator: Jenerette, G. Darrel
Originator: Shulman, Hannah B.
Originator: Piper, Stephanie
Originator: Greene, Aral C.
Originator: Andrews, Holly M.
Originator: Botthoff, Jon
Originator: Sickman, James O.
Originator: Aronson, Emma L.
Originator: Homyak, Peter M.
Publication_Date: 2023
Title:
Nitrous oxide emission and isotopic composition data from four dryland sites in Southern California
Geospatial_Data_Presentation_Form: tabular digital data
Publication_Information:
Publication_Place: Fort Collins, CO
Publisher: Forest Service Research Data Archive
Online_Linkage: https://doi.org/10.2737/RDS-2023-0021
Description:
Abstract:
This data publication includes in-situ nitrous oxide and nitric oxide emissions measured in four dryland sites in Southern California between June 2019 and August 2020. Emissions were measured from eight locations within each site every 15 minutes after experimentally adding water and ¹⁵N labeled nitrate or ammonium to the soils. We report nitrous oxide and nitric oxide emissions from two of the sites in 2019, and nitrous oxide from all four sites in 2020. Dry soils from three of the sites were used to measure the abundance of nitrate reducing genes and transcripts using quantitative polymerase chain reaction (qPCR). We also collected soils from the most arid site to conduct two lab experiments in 2022. In July 2022, we incubated a subset of the dry soils with chloroform to inhibit microbial activity. Then we added ¹⁵N labeled nitrate tracer to chloroform fumigated and control soils and measured the isotopic composition of nitrous oxide emitted from these soils every 20 minutes in response to experimental rewetting. In December 2022, we conducted a second lab experiment to measure the natural abundance isotopic composition of nitrous oxide produced in the lab. Data are provided as individual tabular files containing: field nitrous oxide fluxes, field nitric oxide fluxes, field nitric oxide isotopes, qPCR gene and transcript abundance, chloroform inhibition nitrous oxide data, and natural abundance isotope data.
Purpose:
The purpose of this study was to identify the processes that produce nitrous oxide (a potent greenhouse gas) and nitric oxide (an air pollutant) emissions from dryland ecosystems in Southern California.
Supplemental_Information:
For more information about this study and these data, see Krichels et al. (2023).

These data were originally published on 09/07/2023. On 12/07/2023, metadata was updated to include reference to the newly published Krichels et al. (2023).
Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 201906
Ending_Date: 202212
Currentness_Reference:
Ground condition
Status:
Progress: Complete
Maintenance_and_Update_Frequency: As needed
Spatial_Domain:
Description_of_Geographic_Extent:
Southern California
Bounding_Coordinates:
West_Bounding_Coordinate: -116.75770
East_Bounding_Coordinate: -115.72330
North_Bounding_Coordinate: 33.94400
South_Bounding_Coordinate: 33.89610
Bounding_Altitudes:
Altitude_Minimum: 1680
Altitude_Maximum: 2400
Altitude_Distance_Units: feet
Keywords:
Theme:
Theme_Keyword_Thesaurus: ISO 19115 Topic Category
Theme_Keyword: environment
Theme:
Theme_Keyword_Thesaurus: National Research & Development Taxonomy
Theme_Keyword: Climate change
Theme_Keyword: Ecology, Ecosystems, & Environment
Theme_Keyword: Soil
Theme:
Theme_Keyword_Thesaurus: None
Theme_Keyword: nitrous oxide
Theme_Keyword: denitrification
Theme_Keyword: chemodenitrification
Theme_Keyword: drylands
Place:
Place_Keyword_Thesaurus: None
Place_Keyword: California
Access_Constraints: None
Use_Constraints:
These data were collected using funding from the U.S. Government and can be used without additional permissions or fees. If you use these data in a publication, presentation, or other research product please use the following citation:

Krichels, Alexander H.; Jenerette, G. Darrel; Shulman, Hannah B.; Piper, Stephanie; Greene, Aral C.; Andrews, Holly M.; Botthoff, Jon; Sickman, James O.; Aronson, Emma L.; Homyak, Peter M. 2023. Nitrous oxide emission and isotopic composition data from four dryland sites in Southern California. Fort Collins, CO: Forest Service Research Data Archive. https://doi.org/10.2737/RDS-2023-0021
Point_of_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USDA Forest Service, Rocky Mountain Research Station
Contact_Person: Alexander Krichels
Contact_Position: Research Ecologist
Contact_Address:
Address_Type: mailing and physical
Address: 333 Broadway SE Suite 115
City: Albuquerque
State_or_Province: NM
Postal_Code: 87102
Country: USA
Contact_Voice_Telephone: 505-724-3665
Contact_Electronic_Mail_Address: alexander.krichels@usda.gov
Contact Instructions: This contact information was current as of original publication dates. For current information see Contact Us page on: https://doi.org/10.2737/RDS.
Data_Set_Credit:
This project was funded by the National Science Foundation (DEB 1916622 and DEB 1656062) and the USDA Forest Service, Rocky Mountain Research Station.


Author Information:

Alexander H. Krichels
USDA Forest Service, Rocky Mountain Research Station
https://orcid.org/0000-0002-6922-6476

G. Darrel Jenerette
University of California
https://orcid.org/0000-0003-2387-7537

Hannah B. Shulman
University of Tennessee
https://orcid.org/0000-0002-9959-9417

Stephanie Piper
University of California

Aral C. Greene
University of California
https://orcid.org/0000-0003-1009-5165

Holly M. Andrews
University of California
https://orcid.org/0000-0002-5173-0826

Jon Botthoff
University of California

James O. Sickman
University of California

Emma L. Aronson
University of California
https://orcid.org/0000-0002-5018-2688

Peter M. Homyak
University of California
https://orcid.org/0000-0003-0671-8358
Cross_Reference:
Citation_Information:
Originator: Krichels, Alexander H.
Originator: Jenerette, G. Darrel
Originator: Shulman, Hannah B.
Originator: Piper, Stephanie
Originator: Greene, Aral C.
Originator: Andrews, Holly M.
Originator: Botthoff, Jon
Originator: Sickman, James O.
Originator: Aronson, Emma L.
Originator: Homyak, Peter M.
Publication_Date: 2023
Title:
Bacterial denitrification drives elevated N₂O emissions in arid Southern California drylands
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Science Advances
Issue_Identification: 9(49)
Online_Linkage: https://doi.org/10.1126/sciadv.adj1989
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Data_Quality_Information:
Attribute_Accuracy:
Attribute_Accuracy_Report:
The authors are confident in the accuracy of these data. All instruments were calibrated with reference standards prior to use. The authors used a custom instrument array to measure trace gas emissions in the field. While the authors are confident in this setup, it has not been used by other researchers. The authors used published protocols for all lab experiments and are confident in their results. Unless otherwise noted, data should be accurate to three significant digits.
Logical_Consistency_Report:
All emission data were checked for linearity.
Completeness_Report:
"NA" values mean that data were not collected for a given measurement. This was usually due to instrument failure.

Data were not always measured on all sites, see methodology section for details.
Lineage:
Methodology:
Methodology_Type: Field and Lab
Methodolgy_Identifier:
Methodolgy_Keyword_Thesaurus:
None
Methodology_Keyword: isotopes
Methodology_Keyword: isotopocules
Methodology_Keyword: quantitative ploymerase chain reaction
Methodology_Keyword: chloroform inhibition
Methodology_Keyword: field trace gas emissions
Methodology_Description:
SITES DESCRIPTIONS

We studied four sites (site A = Morongo, site B = Oasis, site C = Wide Canyon, and site D = Pinto Basin) across an aridity gradient in Southern California, with site A being the wettest (299 millimeters [mm] mean annual precipitation, or MAP) and D the driest (101 mm MAP). Because of the proximity of our sites to the city of Los Angeles, USA, the sites also fall along an atmospheric nitrogen (N) deposition gradient with the highest N deposition rates occurring in site A. Creosote shrubs (Larrea tridentata) were the dominant vegetation at all sites. Soils were derived from similar granitic parent material but varied in pH, texture, and taxonomy, with site A being the least alkaline and D the most alkaline.


EXPERIMENTAL DESIGN

We measured nitrous oxide (N₂O) emissions from soils underneath eight Creosote shrubs at each of the four sites in July 2019, June 2020, and August 2020. We randomly chose an area that had at least 8 shrubs within a 10 meter (m) radius. Due to rainfall interrupting our rewetting experiments in 2019, we were unable to measure emissions from site B, and we only measured emissions in response to adding NO₃⁻ in site D. Emissions were measured in response to experimentally wetting soils underneath shrubs with 500 milliliters (mL) deionized water with different amounts of dissolved NO₃⁻ or NH₄⁺. The water addition amount was chosen to simulate a 7 mm rain event, approximately the average size of a summer rain event at our sites (https://deepcanyon.ucnrs.org/weather-data/). In 2019 and in site D in 2020, the N solutions were labeled with ¹⁵N-NO₃⁻ or ¹⁵N-NH₄⁺ enriched to 2 atom percent ¹⁵N. We used ascorbic acid to ensure the ¹⁵N-NO₃⁻ solution was free of NO₂⁻ contamination. For all other sampling campaigns, the N additions were not labeled with isotopically enriched ¹⁵N. Measurements were made underneath shrub canopies to capture “islands of fertility” where soil nutrients are concentrated. The shrubs were separated from one another by at least 1 m and were all within a 10 m radius. Under each shrub canopy, two pairs of polyvinyl chloride (PVC) collars (4 collars total; 20 centimeter [cm] diameter × 10 cm height) were inserted 5 cm into the ground at least 48 hours prior to starting measurements. One collar within each pair was wetted with NO₃⁻ solution, while the other was wetted with NH₄⁺ solution. Nitrogen concentrations in the wetting solutions corresponded to a range in annual N deposition rates observed in Southern California drylands so that each shrub received a different amount of N: 0, 10, 20, 30, 40, 50, 60, or 70 kilograms Nitrogen per hectare (kg-N ha⁻¹). Collar pairs were installed at least 1 m apart, limiting cross-contamination of isotope tracers between collars. N₂O emissions were measured from the collars that were amended with N. The collars that were not amended with N were wetted with 500 mL of water at the same time that the N solution was added to the other collar within each pair; these collars were used to measure soil temperature (Model 8150-203, LI-COR Biosciences) and moisture (Model 8150-205, LI-COR Biosciences) to avoid disturbing the soils under the collars that were used to measure N₂O emissions. The NO₃⁻ solution was added to soils at approximately 9:00 AM with N₂O emissions measured from each shrub every 30 minutes over 24 hours, starting 15 minutes after wetting. This was then repeated with the NH₄⁺ solution the following morning using the other pair of collars underneath each shrub.


FIELD N₂O EMISSIONS (\Data\2019_2020_Combined_N2O.csv)

An automated chamber system was used to simultaneously measure N₂O emissions from one of the collars under each of the eight shrubs. Each shrub was equipped with its own automated chamber (8100-104, LI-COR Biosciences, Lincoln, NE) connected to a multiplexer to automate the measurements (LI-8150, LI-COR Biosciences); chambers were measured sequentially so that fluxes were measured from each shrub every 30 minutes. While a given chamber was closed, gas was recirculated through a sample loop for two minutes. The sample loop connected the multiplexer to an infrared gas analyzer (IRGA; LI-8100, LI-COR Biosciences) and an isotope N₂O analyzer (Model 914-0027, Los Gatos Research, Inc., Mountain View, CA). The instruments were kept in an air-conditioned box made from insulation boards (5 cm thick; 5 x 2 x 2 m). A water trap was also included in the sample loop to prevent condensation inside tubing lines fed to instruments during the transition from ambient conditions into the air-conditioned box. The IRGA and N₂O analyzer sampled air from the recirculating sample loop and a vent in the chamber allowed for ambient air to enter the sample loop and prevent changes in chamber pressure (see supplementary information in Davidson et al. 1991 for full description of sample loop). Diluting the sample loop with ambient air did not appreciably affect flux measurements since the amount of air entering the chamber over the relatively short two-minute measurement was small relative to the volume of the sample loop (approximately 6 liters [L]) and the change in N₂O concentrations was linear (mean R² = 0.80 when N₂O flux > 1 nanogram N-N₂O per square meters per second [ng N-N₂O m⁻² s⁻¹]) throughout the measurements, especially when N₂O emissions were high (mean R² = 0.98 when N₂O flux > 10 ng N-N₂O m⁻² s⁻¹) (Davidson et al. 1991).

Field N₂O emissions were calculated as the linear change in concentrations over the last 90 seconds of the two-minute incubation (Andrews and Krichels 2022). Net emissions were reported as zero if the linear correlation between time and trace gas concentration was not statistically significant (p > 0.05). The isotopic N₂O analyzer measured δ¹⁵N but since our measurements were diluted with ambient air, we do not attempt to calculate absolute δ¹⁵N values. Rather, for our field measurements, we calculate the average δ¹⁵N during the final 10 seconds of each incubation (hereafter referred to as *δ¹⁵N and report this as an index of the time it took the ¹⁵N tracer to be oxidized or reduced into N₂O and detected by our analyzer. These processed data are included in \Data\2019_2020_Combined_N2O.csv.


FIELD NO EMISSIONS (\Data\2019_NO_data.csv and \Data\2020_Combined_NO_Ogawa_Isotopes.csv)

A nitric oxide (NO) analyzer (Model 410 and Model 401, 2B Technologies, Boulder CO) was connected to the field sample loop (described above) for the 2019 field campaign. The NO analyzer sampled air from the recirculating sample loop at a rate of 1 L per minute; the NO analyzer consumed NO and vented air to the atmosphere. A vent in the chamber allowed for ambient air to enter the sample loop and prevent changes in chamber pressure. Field NO emissions were calculated as the linear change in concentrations over the last 90 seconds of the two-minute incubation. Net emissions were reported as zero if the linear correlation between time and trace gas concentration was not statistically significant (p > 0.05). The change in NO concentrations was linear (mean R² = 0.86 for all measurements) especially when NO emissions were high (mean R² = 0.98 when emissions > 100 ng N-NO m⁻² s⁻¹). These processed data are included in \Data\2019_NO_data.csv.

We also measured the conversion of ¹⁵N-NO₃⁻ and ¹⁵N-NH₄⁺ to NO from all four sites in June 2020 using passive samplers (Ogawa pads; Ogawa USA, Pompano Beach, FL). Four separate pairs of collars were installed under four different shrubs. One collar was wet with ¹⁵N-NO₃⁻ solution on the first day of the experiment, and the other was wet with ¹⁵N-NH₄⁺ solution on the second day of the experiment. Passive NOₓ and nitrite (NO₂) sampling pads were installed within closed chambers for two discrete time periods post wetting: 0–15 minutes and 15 minutes–24 hours. Two sampling pads were left in sealed plastic bags throughout the experiment, these are referred to as “blanks”. The chambers were sealed with a rubber lid to prevent gas from escaping during the incubation. The passive sampling pads were stored in plastic bags and transported to the lab to measure NOₓ concentration and isotopic composition. The NOₓ from the pads was extracted as NO₂⁻ in 8 mL deionized water and the solution was analyzed for NO₂⁻ concentrations (SEAL method EPA-137-A, https://www.seal-analytical.com/Methods/Discrete-Methods/AQ2-EPA-Methods); no NO₂⁻ was detected on the NO₂ pads, suggesting the NOₓ pads exclusively collected NO. ¹⁵N-NO composition was then measured by converting the extracted NO₂⁻ to N₂O using Pseudomonas aureofaciens and analyzing the N₂O for δ¹⁵N using a Thermo Delta V isotope ratio mass spectrometer (Thermo Fisher Scientific, Woltham, MA) at the Facility for Isotope Ratio Mass Spectrometry (FIRMS; https://ccb.ucr.edu/facilities/firms) at the University of California, Riverside.


narG GENE AND TRANSCRIPT ABUNDANCE (\Data\cDNA_data.csv)

We extracted nucleic acids from approximately 2 grams (g) of soil collected underneath four shrubs from sites A and C in 2019, and site D in 2020. We did not sample site B because of limited resources; site B is relatively close to site C, so we omitted site B to maximize differences among sites. To ensure accurate capture of genes and transcripts, soils were collected in tandem with the automated chambers, immediately frozen in liquid nitrogen in the field, and stored at -80 degrees Celsius (°C) until further processing. The Qiagen RNeasy PowerSoil Total RNA kit was used to extract RNA, and then DNA was extracted from the supernatant using the PowerSoil DNA Elution Kit, both following manufacturer’s guidelines. To prepare nucleic acids for sequencing, RNA extracts were treated with RQ1 RNase-Free DNase (Promega) and reverse transcribed into cDNA using ProtoScrip II Reverse Transcriptase (New England Biolabs), both following manufacturer’s instructions. We used quantitative polymerase chain reaction (qPCR) to estimate the abundance of narG and napA genes and transcripts. We used the narG1960F/narG2650R primer set for narG (Philippot et al. 2002) and the napA-V17m/napA4R primer set for napA (Bru et al. 2007). The 10 microliter (µL) reactions consisted of 5 µL of Forget-Me-Not EvaGreen qPCR Master Mix (Biotium, Inc., Fremont, CA), 0.8 µL of 2 millimolar (mM) McCl2, 0.25 µL of 0.5 milligrams per milliliter (mg mL⁻¹) BSA, 0.125 µL of 0.25 micrometer (µM) forward and reverse primer, 2.5 µL water (H₂O), and 1.2 µL sample DNA. We used the CFX384 Touch Real-Time PCR Detection System to measure the quantity of narG and napA. All reactions were performed in triplicate. narG was amplified using the following protocol: 5 minutes at 95 °C, followed by 40 cycles of 45 seconds at 95 °C, 30 seconds at 50 °C and 60 seconds at 72 °C. napA was amplified using the following protocol: 4 minutes at 95 °C, followed by 40 cycles of 30 seconds at 95 °C, 45 seconds at 65 °C and 60 seconds at 72 °C.

We calculated the gene copy numbers per gram soil in each sample by running a standard curve in triplicate for each qPCR run. We synthesized known sequences of napA (NCBI Reference Sequence: NC_000913.3) and narG (NC_002945.4) using gBlocks HiFi gene fragments (Integrated DNA Technologies) to create the standards. We validated that the primers amplified the same size of PCR product in the standards and samples using gel electrophoresis. We prepared standard curves using serial dilutions for both narG (2 ng/µL - 0.00002 ng/µL) and napA (10 ng/µL - 0.00001 ng/µL). The narG standards had efficiencies of > 65% (R² = 0.999) and napA standards had efficiencies of > 76% (R² = 0.999).


CHLOROFORM INHIBITIONS EXPERIMENT (\Data\2022_Chloro_data.csv)

To assess the relative contribution of biological and abiotic processes to N₂O production, we slowed microbial activity with chloroform (CHCl₃; an effective soil sterilant that slows the growth and recolonization of microbial communities resuscitating after wetting) (Jenkinson and Powlson 1976) and compared N₂O fluxes between CHCl₃-fumigated and non-fumigated soils from site D - we chose this site because it produced the most N₂O after wetting dry soils in the field, facilitating comparisons between fumigated and non-fumigated samples. This experiment was conducted in July 2022. Briefly, eight soil samples (approximately 200 g; 0–10 cm depth) were collected from underneath eight shrubs representative of our field measurements. From each of the eight samples, we subsampled duplicate 50 g samples and placed them in mesocosms (4 ounce [oz] canning jar); eight were left under ambient conditions in the laboratory and the other eight were incubated in a vacuum-sealed chamber under a CHCl₃ atmosphere for 10 days. Soils inside the incubation chamber were kept under a constant CHCl₃ atmosphere by keeping a beaker with 100 mL of CHCl₃. To enhance the movement of CHCl₃ into soil pores, we created a vacuum inside the chamber for one minute and then allowed ambient air to flush into the chamber; this was repeated daily.

After 10 days under CHCl₃, the mesocosms were removed from the chamber and net N₂O emissions were measured from fumigated and non-fumigated mesocosms over the course of an experimental wetting event. We also added ¹⁵N-NO₃⁻ to the mesocosms to assess if CHCl₃ fumigation decreased the conversion of NO₃⁻ to N₂O. The ¹⁵N-NO₃⁻ was dissolved in deionized water and mesocosms were wet with 10 mL of this solution (2 atom percent ¹⁵N; 10 µg N-NO₃⁻ g⁻¹ dry soil). Prior to wetting, mesocosms were placed in a 40 °C water bath to simulate summer temperatures at site D. To measure net N₂O emissions during the incubation, the headspace from each mesocosm was dried using a Nafion dryer (PD-200T-12MPS, Perma Pure LLC, Lakewood Township, NJ, USA) and recirculated through a sample loop connected to a multiplexer (LI-8150, LI-COR Biosciences) and an isotope N₂O analyzer (Model 914-0027, Los Gatos Research, Inc., Mountain View, CA). Gas was recirculated through the closed sample loop at a rate of 1.5 L per minute. Net N₂O emissions were calculated as the linear change in N₂O concentration over the 2-minute incubation period. Four jars were connected to the multiplexer at once and emissions were measured from each jar every 15 minutes, starting 5 minutes before wetting each mesocosm and continuing for at least 8 hours. The δ¹⁵Nᵇᵘᶥᵏ emitted from soil was measured using keeling plots; δ¹⁵Nᵇᵘᶥᵏ was calculated as the intercept when plotting the inverse of soil N₂O concentrations on the x-axis versus measured δ¹⁵N on the y-axis (Keeling 1958). We corrected δ¹⁵Nᵇᵘᶥᵏ values for known N₂O and carbon dioxide (CO₂) mass dependencies using instrument specific calibration curves developed using established methods (Harris et al. 2020). The calibration curves were created by analyzing δ¹⁵Nᵇᵘᶥᵏ of a certified standard referenced against USGS 51 and 52 isotope reference materials (Reston Stable Isotope Laboratory; Reston, Virginia, USA), while varying N₂O concentration between (0.4 to 5 parts per million [ppm]) across three different CO₂ concentrations (330, 660, and 990 ppm).


NATURAL ABUNDANCE N₂O ISOTOPE LAB EXPERIMENT (\Data\2022_Gas_Bag_Isotopes.csv)

We conducted a second laboratory incubation experiment to investigate the processes producing N₂O in soils from site D using the natural abundance isotopic composition of N₂O (SP, δ¹⁵Nᵇᵘᶥᵏ, and δ¹⁸O) over the course of an experimental wetting event. The lab experiment was conducted in December 2022. The isotopic composition of N₂O was measured after adding water to air-dried soils (50 g; n = 6) to raise the gravimetric water content to 20%, which is comparable to observed increases in soil moisture in response to wetting soils in the field. Soils were incubated in closed mesocosms (4 oz glass canning jar) at 40 °C; each mesocosm was purged with zero air and connected to a 1-L foil gas bag (Cali-5-Bond; Calibrated Instruments, LLC; McHenry, MD) filled with zero air for the duration of the incubation. Following the six-hour incubation, gas from the mesocosm headspace and gas bag were thoroughly mixed by pumping the mesocosm headspace for one minute with a 60 mL syringe. After mixing, the gas bag was detached from the mesocosm and attached to our LGR N₂O isotope analyzer for analysis.

The LGR isotope analyzer was set to withdraw sample air from each 1-L gas bag at 80 mL minute-1 for ~12 minutes, recording N₂O concentrations and isotope values every second. To avoid interferences caused by CO₂, volatile organic compounds (VOCs), and water vapor on N₂O isotope measurements, the gas passed through a CO₂ trap (Carbosorb; Elemental Microanalysis, Okehampton, UK), a VOC trap (silica gel and activated charcoal; Sigma-Aldrich, St Louis, MO, USA) and a Nafion water trap (PD-200T-12MPS, Perma Pure LLC, Lakewood Township, NJ, USA) before entering the N₂O analyzer (Stuchiner et al. 2021). To calculate isotope values (SP, δ¹⁵Nᵇᵘᶥᵏ, and δ¹⁸O), we averaged the last approximately 3 minutes of our 1-second observations from each gas bag. We corrected our data using a standard curve made with USGS 51 (δ¹⁵N = 1.32 ‰, δ¹⁵Nα = 0.48, δ¹⁵Nβ = 2.15, SP = -1.67 ‰, δ¹⁸O = 41.23 ‰) and USGS 52 (δ¹⁵N = 0.44 ‰, δ¹⁵Nα = 13.52, δ¹⁵Nβ = -12.64, SP = 26.15 ‰, δ¹⁸O = 40.64 ‰) N₂O isotope reference materials (Reston Stable Isotope Laboratory; Reston, Virginia, USA). Individual standard curves were made for three isotopocules of N₂O: ¹⁵N¹⁴N¹⁶O, ¹⁴N¹⁵N¹⁶O, and ¹⁴N¹⁴N¹⁸O (Stuchiner et al. 2021). The standard curves were highly linear (R² > 0.99) between 0.6 and 7 ppm N₂O; the final N₂O concentration in all the gas bags was within this range. The corrected concentration of each isotopocule was converted into delta notation for interpretation. As a measure of uncertainty, averaging 1-second values for 3 minutes (n = 180) at the N₂O concentration range of our samples (630-8072 parts per billion [ppb]), produced coefficients of variation < 2.9 % for all measured isotopes. The data reported in \Data\2022_Gas_Bag_Isotopes.csv shows the corrected N₂O concentration (SP, δ¹⁵Nᵇᵘᶥᵏ, δ¹⁵Nᵅ, δ¹⁵Nᵝ, and δ¹⁵O) from each jar during the incubation.


For additional details see Krichels et al. (2023).
Methodology_Citation:
Citation_Information:
Originator: Andrews, Holly M.
Originator: Krichels, Alexander H.
Publication_Date: 2022
Title:
Handr003/TraceGasArray: v1.1
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Publication_Information:
Publisher: Zenodo
Online_Linkage: https://doi.org/10.5281/zenodo.7246428
Methodology_Citation:
Citation_Information:
Originator: Bru, D.
Originator: Sarr, A.
Originator: Philippot, Laurent
Publication_Date: 2007
Title:
Relative abundances of proteobacterial membrane-bound and periplasmic nitrate reductases in selected environments
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Applied and Environmental Microbiology
Issue_Identification: 73(18): 5971–5974
Online_Linkage: https://doi.org/10.1128/AEM.00643-07
Methodology_Citation:
Citation_Information:
Originator: Davidson, Eric A.
Originator: Vitousek, Peter M.
Originator: Matson, Pamela A.
Originator: Riley, Ralph
Originator: García-Méndez, Georgina
Originator: Maass, J. Manuel
Publication_Date: 1991
Title:
Soil emissions of nitric oxide in a seasonally dry tropical forest of México
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Journal of Geophysical Research: Atmospheres
Issue_Identification: 96(D8): 15439-15445
Online_Linkage: https://doi.org/10.1029/91JD01476
Methodology_Citation:
Citation_Information:
Originator: Harris, Stephen J.
Originator: Liisberg, Jesper
Originator: Xia, Longlong
Originator: Wei, Jing
Originator: Zeyer, Kerstin
Originator: Yu, Longfei
Originator: Barthel, Matti
Originator: Wolf, Benjamin
Originator: Kelly, Bryce F. J.
Originator: Cendón, Dioni I.
Originator: Blunier, Thomas
Originator: Six, Johan
Originator: Mohn, Joachim
Publication_Date: 2020
Title:
N₂O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Atmospheric Measurement Techniques
Issue_Identification: 13(5): 2797-2831
Online_Linkage: https://doi.org/10.5194/amt-13-2797-2020
Methodology_Citation:
Citation_Information:
Originator: Jenkinson, D.S.
Originator: Powlson, D.S.
Publication_Date: 1976
Title:
The effects of biocidal treatments on metabolism in soil—VI. Fumigation with chloroform
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Soil Biology and Biochemistry
Issue_Identification: 8(5): 375-378
Online_Linkage: https://doi.org/10.1016/0038-0717(76)90036-5
Methodology_Citation:
Citation_Information:
Originator: Keeling, Charles D.
Publication_Date: 1958
Title:
The concentration and isotopic abundances of atmospheric carbon dioxide in rural areas
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Geochimica et Cosmochimica Acta
Issue_Identification: 13(4): 322-334
Online_Linkage: https://doi.org/10.1016/0016-7037(58)90033-4
Methodology_Citation:
Citation_Information:
Originator: Krichels, Alexander H.
Originator: Jenerette, G. Darrel
Originator: Shulman, Hannah B.
Originator: Piper, Stephanie
Originator: Greene, Aral C.
Originator: Andrews, Holly M.
Originator: Botthoff, Jon
Originator: Sickman, James O.
Originator: Aronson, Emma L.
Originator: Homyak, Peter M.
Publication_Date: 2023
Title:
Bacterial denitrification drives elevated N₂O emissions in arid Southern California drylands
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Science Advances
Issue_Identification: 9(49)
Online_Linkage: https://doi.org/10.1126/sciadv.adj1989
Methodology_Citation:
Citation_Information:
Originator: Philippot, Laurent
Originator: Piutti, Séverine
Originator: Martin-Laurent, Fabrice
Originator: Hallet, Stéphanie
Originator: Germon, Jean Claude
Publication_Date: 2002
Title:
Molecular analysis of the nitrate-reducing community from unplanted and maize-planted soils
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Applied and Environmental Microbiology
Issue_Identification: 68(12): 6121–6128
Online_Linkage: https://doi.org/10.1128/AEM.68.12.6121-6128.2002
Methodology_Citation:
Citation_Information:
Originator: Stuchiner, Emily R.
Originator: Weller, Zachary D.
Originator: von Fischer, Joseph C.
Publication_Date: 2021
Title:
An approach for calibrating laser-based N₂O isotopic analyzers for soil biogeochemistry research
Geospatial_Data_Presentation_Form: journal article
Series_Information:
Series_Name: Rapid Communications in Mass Spectrometry
Issue_Identification: 35(3): e8978
Online_Linkage: https://doi.org/10.1002/rcm.8978
Process_Step:
Process_Description:
See methodology section
Process_Date: Unknown
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Entity_and_Attribute_Information:
Overview_Description:
Entity_and_Attribute_Overview:
Below you will find a list and description of the files included in this data publication.


VARIABLE DESCRIPTION FILE (1)

1. \Data\_variable_descriptions.csv: Comma-separated values (CSV) file containing a list and description of variables found in all data files. (A description of these variables is also provided in the metadata below.)

Columns include:

Filename = Name of data file
Variable = Name of variable
Units = Units (if applicable)
Precision = Precision (if applicable)
Description = Description of variable


DATA FILES (6)

1. \Data\2019_2020_Combined_N2O.csv: CSV file containing field N₂O emission, soil temperature, soil moisture, and ¹⁵N-N₂O data collected from sites A, C, and D in 2019 and all four sites in 2020.

Variables include:

Port = Port number of the multiplexor (1-8). Each port was connected to a different chamber, which was underneath a different shrub. Port 1 received the lowest N addition amount and pot 8 received the highest.

Date = Date and time when a given measurement ended (mm/dd/yyyy hh:mm:ss)

TimeSinceWetting = Time that elapsed since water was added to a given collar (s). Negative values indicate that a measurement took place before soils were wet.

ChamberTemp = Temperature inside the chamber at the given time (degrees Celsius [°C])

Moisture = Volumetric water content at 10 centimeters (cm) depth from an adjacent collar at the given time

rCO2 = Coefficient of determination for the relationship between time and CO₂ conentration over the last 90 seconds the chamber was closed

rN2O = Coefficient of determination for the relationship between time and N₂O conentration over the last 90 seconds the chamber was closed

CO2flux = Emission of carbon dioxide from the collar (micrograms of carbon – carbon dioxide per square meters per second [ugC-CO₂/m²/s])

N2Oflux = Emission of nitrous oxide from the collar (micrograms of nitrogen – nitrous oxide per square meters per second [ugN-N₂O/m²/s])

Site = Site that was measured (A = Morongo, B = Oasis, C = Wide Canyon, D = Pinto Basin)

N_form = Wjether nitrate (NO₃) or ammonium (NH₄) was added to a given collar

SoilTemp = Soil temperature at approximately 5 cm depth from an adjacent collar at the given time (°C)

Year = General time when the measurements were conducted (month and year)

d15N = Isotopic composition of the N₂O emitted during the incubation (parts per thousand [per mil])


2. \Data\2019_NO_data.csv: CSV file containing field NO emission, soil temperature, and soil moisture collected from sites A and C in 2019.

Variables include:

Port = Port number of the multiplexor (1-8). Each port was connected to a different chamber, which was underneath a different shrub. Port 1 received the lowest N addition amount and pot 8 received the highest.

Date = Date and time when a given measurement ended (mm/dd/yyyy hh:mm:ss)

TimeSinceWetting = Time that elapsed since water was added to a given collar (s). Negative values indicate that a measurement took place before soils were wet.

ChamberTemp = Temperature inside the chamber at the given time (°C)

Moisture = Volumetric water content at 10 centimeters (cm) depth from an adjacent collar at the given time

NOflux = Emission of nitric oxide from the collar (nanograms of nitrogen – nitric oxide per square meters per second [ngN-NO/m²/s])

SoilTemp = Soil temperature at approximately 5 cm depth from an adjacent collar at the given time (°C)

Site = Site that was measured (A, C)


3. \Data\2020_Combined_NO_Ogawa_Isotopes.csv: CSV file containing ¹⁵N isotopic composition of nitric oxide (NO) emitted from all field sites in 2020.

Variables include:

ID = Unique ID for each shrub where NO isotopes were measured

Site = Site that was measured (A, B, C, D)

N_Form = Whether nitrate (NO₃) or ammonium (NH4) was added to the soil. N additions were enriched to 2 atom percent ¹⁵N.

Tracer Amount = How much Nitrogen (N) (0 or 15 kilograms of Nitrogen per hectare [kgN/ha]) was added to the collar. N was dissolved in 500 milliters (mL) H₂O.

Time = Time since adding water to the soil (0.25Hr = 0.25 hours, 24Hr = 24 hours, Blank = sampling pads that were left in plastic bags during the experiment to quantify contamination of the sampling pads)

d15N = How much ¹⁵N was detected in nitric oxide (per mil)

d18O = How much ¹⁸O was detected in nitric oxide (per mil)


4. \Data\2022_Chloro_data.csv: CSV file containing N₂O emissions and isotopic composition data from soils from site D where microbial activity was inhibited with chloroform in the lab in 2022.

Date = Date and time when a given measurement ended (mm/dd/yyyy hh:mm:ss)

N2Oflux = Emission of nitrous oxide from each jar incubation (micrograms of nitrogen – nitrous oxide per gram dry soil per second [ugN-N₂O/g/s])

d15N = Isotopic composition of the N₂O emitted during the incubation (per mil)

TimeSinceWetting = Time that elapsed since water was added to a given collar (seconds [s]). Negative values indicate that a measurement took place before soils were wet.

Site = Site that was measured (D)

Rep = Identifies each individual jar incubation (1-8)

Treatment = Which jars were treated with chloroform (Chloro) and which were not (Control)


5. \Data\2022_Gas_Bag_Isotopes.csv: CSV file containing natural abundance N₂O isotope data from soils collected from site D that were incubated in the lab in 2022.

Variables include:

ID = Replicate number for a given jar incubation (all soils are from Site D)

N2O = Concentration of N₂O in the gas bag (parts per million [ppm])

d15NA = Isotopic composition of N in the alpha position of the N₂O molecule (per mil)

d15NB = Isotopic composition of N in the beta position of the N₂O molecule (per mil)

d18O = Isotopic composition of O in the N₂O molecule (per mil)

d15N = Isotopic composition of the N₂O emitted during the incubation (per mil)

SP = Site preference of N₂O (per mil)


6. \Data\cDNA_data.csv: CSV file containing nitrate reducing gene and transcript copy number data (napA and narG genes) from dry soils collected in the field from sites A, C, and D.

Variables include:

Shrub = ID for the shrub where soil was collected from within a given site (S1, S6, S7, S8)

Site = Site where soil was collected (A, C, D)

narG = How many narG transcripts were in the sample per grams (g) dry soil (copy per g of soil)

narG = How many narG genes were in the sample per g dry soil (copy per g of soil)

napA = How many napA genes were in the sample per g dry soil (copy per g of soil)
Entity_and_Attribute_Detail_Citation:
Krichels, Alexander H.; Jenerette, G. Darre; Shulman, Hannah B.; Piper, Stephanie; Greene, Aral C.; Andrews, Holly M.; Botthoff, Jon; Sickman, James O.; Aronson, Emma L.; Homyak, Peter M. 2023. Bacterial denitrification drives elevated N₂O emissions in arid Southern California drylands. Science Advances. 9(49). https://doi.org/10.1126/sciadv.adj1989
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Distribution_Information:
Distributor:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USDA Forest Service, Research and Development
Contact_Position: Research Data Archivist
Contact_Address:
Address_Type: mailing and physical
Address: 240 West Prospect Road
City: Fort Collins
State_or_Province: CO
Postal_Code: 80526
Country: USA
Contact_Voice_Telephone: see Contact Instructions
Contact Instructions: This contact information was current as of December 2023. For current information see Contact Us page on: https://doi.org/10.2737/RDS.
Resource_Description: RDS-2023-0021
Distribution_Liability:
Metadata documents have been reviewed for accuracy and completeness. Unless otherwise stated, all data and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. However, neither the author, the Archive, nor any part of the federal government can assure the reliability or suitability of these data for a particular purpose. The act of distribution shall not constitute any such warranty, and no responsibility is assumed for a user's application of these data or related materials.

The metadata, data, or related materials may be updated without notification. If a user believes errors are present in the metadata, data or related materials, please use the information in (1) Identification Information: Point of Contact, (2) Metadata Reference: Metadata Contact, or (3) Distribution Information: Distributor to notify the author or the Archive of the issues.
Standard_Order_Process:
Digital_Form:
Digital_Transfer_Information:
Format_Name: CSV
Format_Version_Number: see Format Specification
Format_Specification:
Comma-separated values file
Digital_Transfer_Option:
Online_Option:
Computer_Contact_Information:
Network_Address:
Network_Resource_Name: https://doi.org/10.2737/RDS-2023-0021
Fees: None
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Metadata_Reference_Information:
Metadata_Date: 20231207
Metadata_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USDA Forest Service, Rocky Mountain Research Station
Contact_Person: Alexander Krichels
Contact_Position: Research Ecologist
Contact_Address:
Address_Type: mailing and physical
Address: 333 Broadway SE Suite 115
City: Albuquerque
State_or_Province: NM
Postal_Code: 87102
Country: USA
Contact_Voice_Telephone: 505-724-3665
Contact_Electronic_Mail_Address: alexander.krichels@usda.gov
Contact Instructions: This contact information was current as of original publication dates. For current information see Contact Us page on: https://doi.org/10.2737/RDS.
Metadata_Standard_Name: FGDC Biological Data Profile of the Content Standard for Digital Geospatial Metadata
Metadata_Standard_Version: FGDC-STD-001.1-1999
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