DOI: 10.5061/dryad.cz8w9gjgx
title: Data from: Differential pulse sensitivity of nitric and nitrous oxide emissions to temperature, carbon, and nitrogen following wetting of desert soils

description: Infrequent soil wetting in deserts can induce large nitrogen (N) trace gas
 pulses; however, how other abiotic mechanisms interactively control the
 timing and magnitude of these pulses is not clear. In particular,
 production of nitric (NO) and nitrous (N2O) oxide may be differentially
 dependent on temperature, carbon, and nitrogen availability. At a desert
 field site in southern California, USA, we used an automated sensor system
 in four years of field campaigns to track NO and N2O pulse responses to
 experimental manipulations of carbon (C) and N across a range of ambient
 temperatures and shrub “islands of fertility”. We observed rapid onset and
 shorter duration of N2O pulses immediately after wetting compared to
 lagged and extended pulses of NO, suggesting preferential incorporation of
 N initially into N2O in anoxic microsites and then to NO as soils dry. We
 identified strong nitrogen limitation and exponential temperature
 dependence of NO pulses, particularly for soils located under shrubs. N2O
 pulses were less responsive to experimental manipulations but showed
 evidence of C and N co-limitation as well as seasonal temperature
 differences. As atmospheric N deposition and temperatures continue to
 increase in desert systems, we can expect larger losses of N from soils as
 pulse-based emissions.
description: <strong>2.1 Study site and focal
 species</strong> We conducted five field
 experiments, spanning four years and encompassing both summer and winter
 seasons, at Boyd Deep Canyon Desert Research Center (hereafter “BDC”; Palm
 Desert, California, USA; 33.6480° N, 116.3765° W, 290 meters ASL). BDC is
 situated in Southern California’s Colorado Desert, a subregion of the
 Sonoran Desert, and experiences a climate characterized by hot summers and
 mild winters. Up to 85% of the precipitation at this site occurs in the
 winter season and predominantly as rain, but sporadic heavy rainfall can
 occur in summer associated with North American monsoons. Monthly average
 temperatures in this area range from 12 °C in January and February to 35
 °C in July and August, with temperatures occasionally exceeding 45 °C
 during the summer months. Annual atmospheric nitrogen deposition averages
 4.2 kg ha<sup>-1</sup> yr<sup>-1</sup>, a
 relatively low rate for deserts in the southwestern United States (Schwede
 & Lear, 2014) and globally (Ackerman et al.,
 2019). BDC soils are alkaline with a pH of 8.36 ± 0.19 and are
 classified as stony sand Hyperthermic Typic Torriorthent soils in the
 Carrizo Series. Previous studies conducted at this location have
 identified high spatiotemporal variability of soil C and N pools (Krichels et
 al., 2022; Eberwein et
 al., 2020; Chatterjee and Jenerette, 2011), suggesting hotspots of biogeochemical processes even within experimental replicates. The primary shrub species at Boyd Deep Canyon and focal species in our wetting experiments was creosote bush (<em>Larrea tridentata</em>). These shrubs play a key role in creating fertile “islands” of herbaceous annual plants and soil organic matter amidst sandy interspaces (Schlesinger et al., 1996). In each field campaign, we used <em>L. tridentata</em> shrubs as experimental replicates. However, for each field campaign, we selected a different group of shrubs within BDC to avoid potential legacy effects from previous wetting and substrate modifications. In experiments where we compared soils under shrubs to soils in shrub interspaces, we chose sandy patches located at least 1.5 meters adjacent to focal shrubs as interspace treatments. All wetting experiments were performed when volumetric soil moisture content was below 10 % and the site had not received significant rain for at least three weeks prior. Therefore, it was assumed that differences in NO and N<sub>2</sub>O dynamics between seasons were more likely due to responses to soil temperature rather than antecedent soil moisture levels. <strong>2.2 Soil temperature, moisture, and N trace gas measurement system</strong>              Prior to each field campaign, pairs of polyvinyl chloride (PVC) soil collars measuring 20-cm in diameter were installed to 5-cm depth and adjacent to each other under <em>L. tridentata</em> canopies or in interspaces between shrubs. One collar per pair was designated for trace gas measurements and the other collar was used for soil temperature, moisture, and ancillary soil physicochemistry measurements, where similar climate and edaphic conditions were assumed between collars. Both collars in each pair received identical wetting treatments and collar pairs were situated at least 1.5 meters apart from other pairs. Beginning up to 24 hours prior to wetting, 15 minutes following wetting, and then at 30-minute intervals over the subsequent 24-45 hours, we measured soil temperature, moisture, and NO and N<sub>2</sub>O fluxes using a sensor array that has been previously described in Andrews et al. (2023) and is recounted briefly here. The array consisted of eight automated chambers (LI-8100-104; LI-COR Bioscience, Lincoln, NE, USA) installed on soil PVC collars and attached to soil temperature (LI-8150-203 thermistor probe; LI-COR Bioscience) and moisture (LI-GS1 probe; LI-COR Bioscience) probes. Probes were inserted into adjacent collars to 5 cm below the soil surface and provided integrated measurements of 3-5 cm soil depth. Each chamber measurement sequence included a 30-second pre-measurement purge, a 2.5-minute active measurement period of trace gas concentrations and soil temperature and moisture status, and a 30-second post-measurement purge, where concentrations of N<sub>2</sub>O and NO were measured simultaneously every 1 and 10 seconds, respectively. Air collected from an actively measuring chamber was passed through a multiplexer (LI-8150; LI-COR Bioscience) and delivered to a sequence of calibrated gas analyzers connected in a semi-closed loop: 1) a N<sub>2</sub>O/CO cavity-ringdown infrared spectrometer (Los Gatos Research, San Jose, CA, USA);  2) the LI-8100A; and 3) a coupled nitrogen dioxide (NO<sub>2</sub>) converter and NO monitor (Models 401/410, 2B Technologies, Boulder, CO, USA). The multiplexer, N<sub>2</sub>O/CO analyzer, and LI-8100 formed a closed loop that returned sample air to the active sampling chamber; however, the NO<sub>2</sub>/NO monitor is an open, chemiluminescence-based system, so a portion of air was siphoned from the sample loop through a one-way check valve and was measured as NO (and NO<sub>2</sub>, which was assumed negligible at this study site). Given small chamber volume and short measurement time, we assume a small but non-negligible amount of error introduced into flux calculations by incorporating a controlled NO "leak" in the sample loop (Andrews et al., 2022; Davidson et al., 2000; Davidson et al., 2008). <strong>2.3 Soil extractable carbon and nitrogen pools</strong> In four out of five field experiments, we collected 5-cm<sup>2</sup> x 10-cm deep soil cores from our “ancillary measurements” collars immediately prior to wetting and at 24-48 hours after wetting to track changes in N (ammonium NH<sub>4</sub><sup>+</sup> and the sum of nitrite+nitrate NO<sub>2</sub><sup>-</sup> + NO<sub>3</sub><sup>-</sup>). In Summer 2020, we additionally analyzed soil cores for water-extractable C (dissolved organic carbon DOC). Following standard extraction techniques (Carter and Gregorich, 2006), each core of fresh soil was homogenized in a plastic bag, sealed, and transported to the lab on ice. For inorganic N analysis, one subset of each soil sample was extracted in 1:10 soil weight:solution volume ratio of 2 M KCl solution. For DOC analysis, a second subset of each sample was extracted in 1:5 soil weight:solution volume ratio of deionized water. Extracts were shaken for 1 h, centrifuged, and gravity-filtered through 11-micron filter paper at room temperature. NH<sub>4</sub><sup>+</sup> quantification was performed via phenate method and NO<sub>2</sub><sup>-</sup>+NO<sub>3</sub><sup>-</sup> quantification was performed via acidification and automated cadmium coil reduction (AQ2 Discrete Analyzer, Seal Analytical Inc.; Mequon, Wisconsin). DOC quantification was performed via acidification and sparging methods (TOC-V, Shimadzu, Kyoto, Japan). All C and N extracted concentrations were normalized to gravimetric water content (GWC), which was measured as the difference between masses of field-moist soil and oven-dried soil, divided by dry soil mass. <strong>2.4 Experimental design</strong>              We conducted five field campaigns at BDC to identify temperature and substrate drivers of NO and N<sub>2</sub>O pulses at multiple temporal and spatial scales. These experiments have been previously described in Andrews et al. (2023), for which soil CO<sub>2</sub> pulse dynamics were reported, and will be recounted in brief. Four campaigns explicitly tested interactions among temperature and C and/or N limitation of N pulses at seasonal timescales. An additional summer campaign measured N pulse responses across a diel temperature range to explore fine-scale temperature controls over pulse responses to wetting. <strong>2.4.1 Interactive temperature-substrate manipulation experiments</strong> Four of five field experiments were substrate addition experiments conducted at BDC during 2018-2021 to evaluate individual and interactive seasonal temperature and substrate controls on soil NO and N<sub>2</sub>O flux responses to wetting. In 2018, two campaigns evaluated non-factorial combinations of wetting with water alone, with water plus N (Winter 2018 only), and with water plus C and N (Summer 2018 only). In Summer 2020 and Winter 2021, we extended these studies by conducting two fully-factorial experiments which quantified pulse responses to wetting alone, wet+C, wet+N, and wet+C+N amendments in summer and winter seasons. All wetting experiments began during mid-morning hours (8:30-10:00) and tracked soil temperature, moisture, and NO and N<sub>2</sub>O fluxes over subsequent 45-hour periods under 3-4 <em>L. tridentata</em> shrubs and in adjacent interspaces. All soils were wetted by hand to simulate a 2-cm rain event (1.5L), representing a medium-sized event for the site (5-year event size mean = 0.6 cm, min = 0.03 cm, max = 6.3 cm; WRCC, 2021). C and N amendments were added as aqueous dextrose (30 g/L; 2406.4 kg C ha<sup>-1</sup>) and ammonium-nitrate (13 g/L; 912 kg N ha<sup>-1</sup>) solutions, respectively. These C and N concentrations are much larger than naturally-occurring deposition rates and were chosen to help overcome C and N limitation, allowing us to compare the potential sensitivity of nitrification and denitrification between endpoints of resource availability. <strong>2.4.2 Fine-scale temperature manipulation experiment</strong> Expanding on observations of strong pulse responses to summer wetting in 2018, we conducted a fifth field experiment in Summer 2019 to explore temperature-pulse relationships at fine temporal scales. In this experiment, we wetted soils at different hours of the day and quantified how temperature at time of wetting influenced NO and N<sub>2</sub>O pulses. Soil collars were installed in cardinal directions around 8 focal <em>L. tridentata</em> shrubs, where 2 shrubs constituted a treatment replicate containing all hour-of-day treatments. Within each 2-shrub replicate, collars were wetted with water at 3-hour intervals (0:00, 3:00, 6:00, 9:00, 12:00, 15:00, 18:00, 21:00), one collar per hour treatment (collars were not wetted more than once), and were measured for 24 hours post-wetting. <strong>2.5 Data processing and statistical methods</strong> Raw NO and N<sub>2</sub>O concentration and soil probe measurements were batch processed into fluxes and associated soil temperature and moisture data using algorithms adapted from previous work using this chamber array (Andrews et al., 2023; Andrews et al., 2022; Krichels et al., 2022). Instantaneous fluxes of NO and N<sub>2</sub>O were calculated as the regression coefficient of linear increase in gas concentration data during the 2.5-minute active chamber measurement period, accounting for soil collar dimensions and atmospheric parameters following the Ideal Gas Law (Davidson et al., 2000). Fluxes were compiled and integrated with instantaneous soil temperature and moisture measurements using a publicly-available R script (Andrews and Krichels, 2021). Additional post-processing filtering steps were conducted when data failed to cross a threshold of data quality and control due to chamber or analyzer malfunctions. Our final five-campaign dataset consisted of 7972 NO and N<sub>2</sub>O fluxes with corresponding soil temperature and/or moisture measurements. From continuous measurements of each chamber, we constructed 24-hour time series following wetting and extracted the magnitude and timing of maximum instantaneous flux. We also calculated 24-hour total NO and N<sub>2</sub>O fluxes using linear trapezoidal integration of chamber observations which occurred at 30-minute intervals. 24-hour total flux measurements were removed from further analysis if, due to previous quality control steps, integration of a total flux was calculated using less than 5 instantaneous flux measurements. Statistical analyses were conducted in JMP 16 and data management and visualization were performed in R 4.1.3 and RStudio. All p-values are reported at ɑ = 0.05. NO and N<sub>2</sub>O fluxes were transformed using the Box-Cox family of transformation as needed to ensure normality of measurements. For boxplots describing pulse behavior following wetting, we included all field measurements. We compared temperature sensitivity of NO and N<sub>2</sub>O pulses from nutrient addition treatments using models (linear, quadratic, or exponential) that generated the highest AIC values. To evaluate interactive season and substrate effects on N pulses, we included field measurements from fully-factorial C and N amendment experiments (Summer 2020, Winter 2021). We constructed general linear models to describe peak and 24-hour total N fluxes as described by season, nutrient addition treatment (wet, wet+C, wet+N, wet+C+N), and their two-way interaction. Post-hoc Tukey’s HSD tests were used to evaluate pulse differences across individual treatments.
description: # Data for: Differential pulse sensitivity of nitric and nitrous oxide
 emissions to temperature, carbon, and nitrogen following wetting of desert
 soils --- Contains two NO and N2O flux files: 1.) N_rawfluxes.txt contains
 raw instantaneous NO and N2O fluxes and accompanying soil temperature,
 moisture, and other metadata measured for all experiments included in the
 associated manuscript. 2.) IntegratedN2ONOFluxes_BoydDeepCanyon.txt
 contains 24-hour integrated measurements of NO and N2O fluxes and
 accompanying soil temperature, moisture, and other metadata measured for
 experiments conducted at Boyd Deep Canyon. ## Description of data and file
 structure 1. N_fluxes.txt data columns: DateTime: Start time of each
 instantaneous measurement (YYYY-MM-DD HH:MM:SS) TSW: Time Since Wetting;
 negative values indicate dry soils prior to experimental wetting, positive
 values indicate amount of time in hours since experimental wetting
 occurred SoilTemp: Soil temperature (degrees Celsius) collected at ~3-5cm
 depth (measured with LI-8150-203 thermistor probe) SoilVWC: Soil
 volumetric water content (%) collected at ~3-5cm depth (measured with
 LI-GS1 probe). Treatment: Re-wetting treatment. All experimental wetting
 treatments were to simulate 2-cm rain event. Ambient = measurement from
 dry soil prior to re-wetting Natural = measurement taken following a
 natural storm event (Summer2018 campaign only) Wet = measurement taken
 following experimental wetting of dry soil with water only Rewet =
 measurement taken following a subsequent experimental wetting event with
 water only (i.e. dry soils were wetted, allowed to dry for a known
 duration, and then re-wetted again) Wet+C = measurement taken following
 experimental wetting of dry soil with aqueous solution of dextrose (30
 g/L) Wet+N = measurement taken following experimental wetting of dry soil
 with aqueous solution of ammonium-nitrate (13 g/L) Wet+C+N = measurement
 taken following experimental wetting of dry soil with aqueous solution of
 dextrose (30 g/L) and ammonium-nitrate (13 g/L) Experiment: Shorthand name
 of experimental campaign
 (Summer2018/Summer2019/Summer2020/Winter2018/Winter2021) ChamberID: Soil
 automated chamber identity (1-8) Location: Microsite location of
 measurement (Sand/Shrub), to delineate islands of fertility. Shrub cover
 was always creosote (Larrea tridentata). WetFreq: Interval in days at
 which soils were re-wetted (0,2,4,6,8), for campaigns where multiple
 re-wetting events took place (Winter2018 and Summer2018 only) WetTime:
 Time of day at which soils were wetted
 (00:00,03:00,06:00,09:00,12:00,15:00,18:00,21:00) for campaigns where
 wetting time was manipulated (Summer 2019) Season: Season in which
 experiments were conducted (summer/winter) NOflux: NO flux (ng NO-N m-2
 s-1), calculated as linear increase in [NO] (ppm) measured every 10
 seconds for 2.5-minute measurement period (measured with 2B Technologies
 combined 401/410 NO2 converter/NO monitor). Negative flux values are
 within instrument error and considered negligible. N2Oflux: N2O flux (µg
 N2O-N m-2 s-1), calculated as linear increase in [N2O] (ppb) measured
 every 1 second for 2.5-minute measurement period (measured with LGR N2O/CO
 cavity-ringdown spectrometer). Negative flux values are within instrument
 error and considered negligible. In this dataset, "NA" values in
 columns of categorical data indicate treatments that were not conducted as
 part of the experimental design for a particular experiment.
 "NA" values in columns of continuous data indicate measurements
 that either were not made at a particular time or measurements that were
 removed during QA/QC due to instrument malfunction. 1.
 IntegratedN2ONOFluxes_BoydDeepCanyon.txt data columns: Chamber: Soil
 automated chamber identity (1-8). Experiment: Shorthand name of
 experimental campaign
 (Summer2018/Summer2019/Summer2020/Winter2018/Winter2021). Wet_Time: Time
 of day at which soils were wetted
 (00:00,03:00,06:00,09:00,12:00,15:00,18:00,21:00) for campaigns where
 wetting time was manipulated (Summer 2019). Treatment: Re-wetting
 treatment. All experimental wetting treatments were to simulate 2-cm rain
 event. Ambient = measurement from dry soil prior to re-wetting Natural =
 measurement taken following a natural storm event (Summer2018 campaign
 only) Wet = measurement taken following experimental wetting of dry soil
 with water only Rewet = measurement taken following a subsequent
 experimental wetting event with water only (i.e. dry soils were wetted,
 allowed to dry for a known duration, and then re-wetted again) Wet+C =
 measurement taken following experimental wetting of dry soil with aqueous
 solution of dextrose (30 g/L) Wet+N = measurement taken following
 experimental wetting of dry soil with aqueous solution of ammonium-nitrate
 (13 g/L) Wet+C+N = measurement taken following experimental wetting of dry
 soil with aqueous solution of dextrose (30 g/L) and ammonium-nitrate (13
 g/L) Location: Microsite location of measurement (Sand/Shrub), to
 delineate islands of fertility. Shrub cover was always creosote (Larrea
 tridentata). Wet_Freq: Interval in days at which soils were re-wetted
 (0,2,4,6,8), for campaigns where multiple re-wetting events took place
 (Winter2018 and Summer2018 only). avgTemp: 24-hour post-wetting mean soil
 temperature (degrees Celsius) collected at ~3-5cm depth (measured with
 LI-8150-203 thermistor probe). maxTemp: 24-hour post-wetting maximum soil
 temperature (degrees Celsius) collected at ~3-5cm depth (measured with
 LI-8150-203 thermistor probe). minTemp: 24-hour post-wetting minimum soil
 temperature (degrees Celsius) collected at ~3-5cm depth (measured with
 LI-8150-203 thermistor probe). avgMoisture: 24-hour post-wetting mean soil
 volumetric water content (%) collected at ~3-5cm depth (measured with
 LI-GS1 probe). maxMoisture: 24-hour post-wetting maximum soil volumetric
 water content (%) collected at ~3-5cm depth (measured with LI-GS1 probe).
 minMoisture: 24-hour post-wetting minimum soil volumetric water content
 (%) collected at ~3-5cm depth (measured with LI-GS1 probe). netN2O:
 24-hour cumulative post-wetting N2O flux (mg N2O-N m-2), calculated using
 area-under-the-curve integration (measured with LGR N2O/CO spectrometer).
 maxN2O: 24-hour maximum post-wetting instantaneous N2O flux (µg N2O m-2
 s-1; measured with LGR N2O/CO spectrometer). minN2O: 24-hour minimum
 post-wetting instantaneous N2O flux (µg N2O m-2 s-1; measured with LGR
 N2O/CO spectrometer). T0Temp: Soil temperature (degrees Celsius) collected
 at ~3-5cm depth immediately prior to wetting (measured with LI-8150-203
 thermistor probe). T0Moisture: Soil volumetric water content (%) collected
 at ~3-5cm depth immediately prior to wetting (measured with LI-GS1 probe).
 TempAtMaxN2O: Soil temperature (degrees Celsius) collected at ~3-5cm depth
 simultaneously with maximum instantaneous N2O flux within each pulse
 (measured with LI-8150-203 thermistor probe). MoistureAtMaxN2O: Soil
 volumetric water content (%) collected at ~3-5cm depth simultaneously with
 maximum instantaneous N2O flux within each pulse (measured with LI-GS1
 probe). maxN2OTSW: Time post-wetting (in hours post-wetting) of maximum
 instantaneous N2O flux within each pulse. Season: Mediterranean climatic
 season in which N pulses were measured (Summer/Winter). netNO: 24-hour
 cumulative post-wetting N2O flux (mg NO-N m-2), calculated using
 area-under-the-curve integration (measured with 2B Technologies combined
 401/410 NO2 converter/NO monitor). maxNO: 24-hour maximum post-wetting
 instantaneous NO flux (ng NO m-2 s-1; measured with 2B Technologies
 combined 401/410 NO2 converter/NO monitor). minNO: 24-hour minimum
 post-wetting instantaneous NO flux (ng NO m-2 s-1; measured with 2B
 Technologies combined 401/410 NO2 converter/NO monitor). TempAtMaxNO: Soil
 temperature (degrees Celsius) collected at ~3-5cm depth simultaneously
 with maximum instantaneous NO flux within each pulse (measured with
 LI-8150-203 thermistor probe). MoistureAtMaxNO: Soil volumetric water
 content (%) collected at ~3-5cm depth simultaneously with maximum
 instantaneous NO flux within each pulse (measured with LI-GS1 probe).
 maxNOTSW: Time post-wetting (in hours post-wetting) of maximum
 instantaneous NO flux within each pulse. maxTSW: Total measurement time
 for each wetting experiment. maxCO2TSW: Time post-wetting (in hours
 post-wetting) of maximum instantaneous CO2 flux within each pulse. In this
 dataset, "NA" values in columns of categorical data indicate
 treatments that were not conducted as part of the experimental design for
 a particular experiment. "NA" values in columns of continuous
 data indicate integrated measures that were not able to be calculated due
 to either low number of measurements (&lt; 3-5 measurements per pulse) or
 measurements that did not pass QA/QC filtering.