DOI: 10.5061/dryad.37pvmcvqz
title: Data from: Signatures of autumn deluges revealed during spring drought in a semi-arid grassland

description: Increases in extremely large precipitation events (deluges) and shifts in
 seasonal patterns of water availability with climate change will both have
 important consequences for ecosystem function, particularly in
 water-limited regions. While previous work in the semi-arid shortgrass
 steppe of northeastern Colorado has demonstrated this ecosystem’s strong
 sensitivity to growing season deluges, our understanding of ecosystem
 responses to deluges during the dormant season is limited. Here, we
 imposed experimental 100 mm deluges (~ 30% of mean annual precipitation)
 in either September or October in a native C4-dominated shortgrass steppe
 ecosystem to evaluate the impact of this post-growing season shift in
 water availability during the autumn and the following growing season.
 Soil moisture for both deluge treatments remained elevated compared with
 ambient levels through April as spring precipitation was atypically low.
 Despite overall low levels of productivity with spring drought, these
 deluges from the previous autumn increased aboveground net primary
 production (ANPP), primarily due to increases with C4 grasses. C3 ANPP was
 also enhanced, largely due to an increase in the annual C3 grass, Vulpia
 octoflora, in the October deluge treatment. While spring precipitation has
 historically been the primary determinant of ecosystem function in this
 ecosystem, this combination of two climate extremes – an extremely wet
 autumn followed by a naturally occurring spring drought – revealed the
 potential for meaningful carryover effects from autumn precipitation. With
 climate change increasing the likelihood of extremes during all seasons,
 experiments that create novel climatic conditions can provide new insight
 into the dynamics of ecosystem functioning in the future.
description: Methods Site Description
 Our study site was in the North American shortgrass steppe at the
 USDA Central Plains Experimental Range in northeastern Colorado, USA (N
 40.8422°, W 104.7156°). Mean annual temperature is 8.6°C (Lauenroth and
 Sala 1992), and mean annual precipitation is 342 mm with only ~20% of
 annual precipitation occurring during the autumn season (Sept. – Nov.;
 Hermance et al. 2015). Growing season precipitation (May – Aug.) accounts
 for majority (~75%) of the annual total. Long-term ANPP is ~75 g
 m<sup>-2</sup> with the majority comprised of perennial C4
 grasses (~75%, primarily <em>Bouteloua gracillis</em> and
 <em>Bouteloua dactyloides</em>) and the remainder including
 perennial C<sub>3</sub> grasses, cool-season annual grasses,
 forbs, and cacti (Hoover et al. 2021). Soil texture at the study site is
 sandy clay loam (Sala et al. 1992), and although the site has a history of
 moderate cattle grazing, the area where this experiment was conducted has
 been protected from large ruminant grazers since 2011 (Post and Knapp
 2020). Experimental Design At the
 beginning of Sept. 2021, we established thirty 1-m<sup>2
 </sup>plots separated by at least 3 m. Plots were randomly assigned
 to one of two deluge treatments or the ambient group (AMB), which received
 only ambient precipitation. Both deluge treatments included the addition
 of 100 mm of water applied over six days during the autumn of 2021 –
 either in Sept. (SEP) or in Oct. (OCT). The timing of these deluges, early
 and late fall, captured partial vs. complete senescence of the dominant
 grasses aboveground. Using long-term precipitation data from this site
 (Hoover and Derner 2020), this amount of precipitation is equivalent to
 two of the wettest autumn months on record (Sept. 1989 and 2013), each of
 which received approximately 100 mm of precipitation.
             Water was applied between Sept. 15-20 and Oct. 20-25
 for the SEP and OCT treatments, respectively, using a hand-held watering
 wand attached to a flow meter and water pump. Over the week, 8 mm of water
 was added on the first day, 24 mm on the second, 18 mm on the third, and
 then 50 mm was applied on day 6. This water application pattern is similar
 to a 7-day high rainfall period observed in Sept. 1989, where rain
 accumulated for seven days with 50 mm recorded on the final day. To
 prevent overland flow off the plots, water was applied several times each
 day with only 4-8 liters of water added at a time. Added water was tested
 for nitrogen levels (American Agricultural Laboratory, Inc., Nebraska,
 USA) and was below US EPA drinking water standards. Besides the deluge
 events, all plots received ambient precipitation (which was well below
 normal – see Results). Measured Responses
             From Sept. 2021 – Aug. 2022, we monitored soil
 moisture, soil CO<sub>2 </sub>efflux (soil respiration), and
 canopy greenness. From Sept. – Nov. 2021 and mid-Mar. – June 2022,
 measurements were made weekly, but during the winter, measurement
 frequency was more variable, ranging from biweekly to monthly intervals.
 This schedule allowed us to capture key phenological stages including
 autumn senescence and spring green-up with higher resolution. In addition,
 we also measured soil nitrogen availability during two separate sampling
 periods – the autumn and the spring – to assess both treatment and
 potential carryover of soil nitrate
 (NO<sub>3</sub><sup>-</sup>) and ammonium
 (NH<sub>4</sub><sup>+</sup><sub>)</sub>. Finally, above-ground net primary production (ANPP) was measured in mid-June to capture early-season plant growth responses.             Soil moisture (volumetric water content, % VWC) was measured using a 20 cm handheld soil moisture time-domain reflectometry probe (Campbell-Scientific Hydrosense II), which integrates soil moisture across the top 20 cm of soil. Because most of the root biomass in this ecosystem is within the upper 20 cm of soil (Milchunas and Lauenroth 1989; Gill et al. 1999; Nelson et al. 2004), this measurement provides a reliable indicator of water available for the dominant grasses. We also used a Sentek Diviner probe (Diviner 2000, Sentek Pty Ltd.) on a subset of the plots to observe soil moisture dynamics to greater depths (0-60 cm with measurements at 10 cm increments).             We monitored canopy phenology with digital repeat photography to estimate canopy greenness (following the methods of Post and Knapp 2019; 2020; Hoover et al. 2022). For each photograph, we placed an iPhone camera directly above a movable 50 x 50 cm frame positioned in the corner of each plot; this image was then cropped to only include the interior area of the frame. The cropped photos were then analyzed with the R package EBImage (Pau et al. 2010), which calculates the average green chromatic coordinate (GCC) index (Filippa et al. 2016). The GCC index accounts for variation in image lighting by computing the greenness relative to the total brightness of each pixel as green / (red + blue+ green) (Filippa et al. 2016).             To measure soil CO<sub>2</sub> efflux, we installed PVC collars (10 cm in diameter, n=5 per treatment) in bare areas between grasses at the beginning of September (2.4 cm belowground, 2 cm aboveground). If any plant growth occurred within the collars during the measurement period, it was removed (clipped to the base) before measurement. We used a 6400-09 soil flux chamber attached to an LI-6400XT (LiCor., Inc, Lincoln NE, USA) to measure soil respiration. Measurements were taken between 8:30hr – 12:30hr local time at ambient CO<sub>2</sub> concentration, humidity, and temperature             Nutrient availability was assessed using Plant Root Simulator probes (PRS, Western Ag Innovations Inc., Saskatoon, Canada) in both the autumn of 2021 and the spring of 2022. These 15 cm x 3 cm probes, buried in the soil with minimal disturbance, utilize either a cation or anion exchange membrane. For the autumn period, one set of probes (anion and cation) was inserted on Sept. 9 and removed on Dec. 3, 2021, in 23 plots (n=8 for SEP and OCT, n=7 for AMB). During the spring period, three sets of probes per plot were inserted on Mar. 16, 2022, and removed on June 22 in the same 23 plots. After removal, samples were washed using deionized water and sent to Western Ag Innovations for extraction. Probes were analyzed for ammonium (NH<sub>4</sub><sup>+</sup>) and nitrate (NO<sub>3</sub><sup>-</sup><sub> )</sub> with a Technicon Autoanalyzer. Values were reported in µgrams 10 cm-<sup>2 </sup>11 weeks<sup>-1.</sup>             Finally, ANPP was estimated in mid-June (June 14-16) in all plots to capture early-season growth (before potential mid- and late-summer rains fell). We harvested all aboveground vegetation within two 0.1 m<sup>2</sup> subplots to ground height, sorted by functional group (C<sub>3 </sub>grass, C<sub>4</sub> grass, forb, or annual C<sub>3</sub> grass). Vegetation was then dried at 60 °C for 48 hours before being weighed to the nearest 0.01g. The previous year’s growth was easily distinguishable from the current year's growth and was excluded.
description: # Data associated with "Signatures of autumn deluges revealed during
 spring drought in a semi-arid grassland" --- Abstract: Increases in
 extremely large precipitation events (deluges) and shifts in seasonal
 patterns of water availability with climate change will both have
 important consequences for ecosystem function, particularly in
 water-limited regions. While previous work in the semi-arid shortgrass
 steppe of northeastern Colorado has demonstrated this ecosystems strong
 sensitivity to growing season deluges, our understanding of ecosystem
 responses to deluges during the dormant season is limited. Here, we
 imposed experimental 100 mm deluges (~ 30% of mean annual precipitation)
 in either September or October in a native C4- dominated shortgrass steppe
 ecosystem to evaluate the impact of this post-growing season shift in
 water availability during the autumn as well the following growing season.
 Soil moisture for both deluge treatments remained elevated compared with
 ambient levels through April as spring precipitation was atypically low.
 Despite overall low levels of productivity with spring drought, these
 deluges from the previous autumn increased aboveground net primary
 production (ANPP), primarily due to increases with C4 grasses. C3 ANPP was
 also enhanced, largely due to an increase in the annual C3 grass, Vulpia
 octoflora, in the October deluge treatment. While spring precipitation has
 historically been the primary determinant of ecosystem function in this
 ecosystem, this combination of two climate extremes an extremely wet
 autumn followed by a naturally-occurring spring drought revealed the
 potential for meaningful carryover effects from autumn precipitation. With
 climate change increasing the likelihood of extremes during all seasons,
 experiments which create novel climatic conditions can provide new
 insights into the dynamics of ecosystem functioning in the future.
 Contact: Olivia Hajek () Data collection
 location: USDA-ARS Central Plains Experimental Range (N 40.8422,
 W104.7156) Data collection time period: 2021-09-10 2022-06-28 File
 information: 9 files are included in this folder. 1. README. Contains
 detailed information regarding files 2-7. File format: .pdf 2. ANPP.
 Aboveground net primary production of the experimental plots collected
 from June 14-16. File format: .csv Variables: Plot: Plot number of sample
 (Plots 1-30, Plot 17 missing) Rep: Experimental replication of sample (0.1
 m2, 2 reps/plot) Trt: Treatment (AMB = Ambient, SEP = September deluge,
 OCT = October deluge) C3: Mass of C3 perennial grasses in sample, in grams
 C4: Mass of C4 perennial grasses in sample, in grams Forb: Mass of forbs
 in sample, in grams Annual: Mass of C3 annual grasses in sample, in grams
 Cactus: Percent cover of cactus in the sample C3_total: Mass of C3
 perennial grasses and C3 annual grasses in sample, in grams Total_biomass:
 Total mass of entire sample, in grams ANPP_total: Aboveground net primary
 production in g m-2 (total_biomass converted to an area) 3. Canopy
 greenness. Plot greenness from repeat digital photography, as calculated
 with the green chromatic coordinate (GCC), capturing the growing season
 phenology dynamics (2021-09-10 2022-06-28). File format: .csv Variables:
 Date: Date of measurement (dd-mm-yy) Plot: Plot number of sample (Plots
 1-30) Trt: Treatment (AMB = Ambient, SEP = September deluge, OCT = October
 deluge) Greenness: Average green chromatic coordinate of the pixels for
 each plot image 4. Soil moisture 20cm. Soil moisture values integrated
 across the upper 20 cm from 2021-09-10 2022-06-28. File format: .csv
 Variables: Date: Date of measurement (dd-mm-yy) Plot: Plot number of
 sample (Plots 1-30) Trt: Treatment (AMB = Ambient, SEP = September deluge,
 OCT = October deluge) VWC: soil moisture measured as the % volumetric
 water content integrated over the upper 20 cm of soil 5. Sentek Soil
 moisture. Soil moisture measured integrated across the upper 20 cm from
 2021-09-10 2022-06-28. File format: .csv Variables: Date: Date of
 measurement (dd-mm-yy) Plot: Plot number of sample (Plots 1-7) Trt:
 Treatment (AMB = Ambient, SEP = September deluge, OCT = October deluge)
 d_10: soil moisture measured as the % volumetric water content at 10 cm
 soil depth d_20: soil moisture measured as the % volumetric water content
 at 20 cm soil depth d_30: soil moisture measured as the % volumetric water
 content at 30 cm soil depth d_40: soil moisture measured as the %
 volumetric water content at 40 cm soil depth d_50: soil moisture measured
 as the % volumetric water content at 50 cm soil depth d_60: soil moisture
 measured as the % volumetric water content at 60 cm soil depth 6. Soil
 respiration. Soil CO2 efflux of the plot in mol CO2 m-2 s-1 from
 2021-09-10 2022-06- 28. File format: .csv Variables: Date: Date of
 measurement (dd-mm-yy) Plot: Plot number of sample (Plots 1-30) Trt:
 Treatment (AMB = Ambient, SEP = September deluge, OCT = October deluge)
 Efflux: CO2 efflux (soil respiration) of the plot in mol CO2 m-2 s-1. 7.
 Nutrient Availability. Availability of different nutrients in the autumn
 (treatment period) and the following spring (response period), measured
 using in-situ PRS cation and anion probes. File format: .csv Variables:
 Season: Corresponds to the season of measurement (either Autumn or Spring)
 Burial Date: Date of probe burial (mm/dd/yy) Retrieval Date: Date of probe
 burial (mm/dd/yy) Plot: Plot number of sample (Plots 1-30) Trt: Treatment
 (AMB = Ambient, SEP = September deluge, OCT = October deluge) * [ ] NO3:
 Nitrate (NO3-) availability in grams 10 cm-2 11 weeks-1. Method detection
 limit is 2 grams 10 cm-2 11 weeks-1. NH4: Ammonium (NH4+) availability in
 grams 10 cm-2 11 weeks-1. Method detection limit is 2 grams 10 cm-2 11
 weeks-1. Ca: Calcium availability in grams 10 cm-2 11 weeks-1. Method
 detection limit is 2 grams 10 cm-2 11 weeks-1. Mg: Magnesium availability
 in grams 10 cm-2 11 weeks-1. Method detection limit is 4 grams 10 cm-2 11
 weeks-1. K: Potassium availability in grams 10 cm-2 11 weeks-1. Method
 detection limit is 4 grams 10 cm-2 11 weeks-1. P: Phosphorus availability
 in grams 10 cm-2 11 weeks-1. Method detection limit is 0.2 grams 10 cm-2
 11 weeks-1. Fe: Iron availability in grams 10 cm-2 11 weeks-1. Method
 detection limit is 0.4 grams 10 cm-2 11 weeks-1. Mn: Manganese
 availability in grams 10 cm-2 11 weeks-1. Method detection limit is 0.2
 grams 10 cm-2 11 weeks-1. Cu: Copper availability in grams 10 cm-2 11
 weeks-1. Method detection limit is 0.2 grams 10 cm-2 11 weeks-1. Zn: Zinc
 availability in grams 10 cm-2 11 weeks-1. Method detection limit is 0.2
 grams 10 cm-2 11 weeks-1. B: Boron availability in grams 10 cm-2 11
 weeks-1. Method detection limit is 0.2 grams 10 cm-2 11 weeks-1. S: Sulfur
 availability in grams 10 cm-2 11 weeks-1. Method detection limit is 2
 grams 10 cm-2 11 weeks-1. Pb: Lead availability in grams 10 cm-2 11
 weeks-1. Method detection limit is 0.2 grams 10 cm-2 11 weeks-1. Al:
 Aluminum availability in grams 10 cm-2 11 weeks-1. Method detection limit
 is 0.4 grams 10 cm-2 11 weeks-1. Cd: Cadmium availability in grams 10 cm-2
 11 weeks-1. Method detection limit is 0.2 grams 10 cm-2 11 weeks-1.