DOI: 10.5061/dryad.rn8pk0pn7
title: Nitrogen enrichment drives accelerative effect of soil heterogeneity on the flowering phenology of a dominant grass

description: Plant phenology is affected by both abiotic conditions (ie. temperature,
 nitrogen enrichment, drought) and biotic conditions (ie. species
 diversity). The degree of spatial heterogeneity in soil resources is known
 to influence community assembly and dynamics, but the relationship between
 resource heterogeneity and phenology, or the potentially interactive
 effects of soil resources on phenology, are less understood. We leveraged
 a tallgrass prairie restoration experiment that has manipulated soil
 nitrogen availability and soil depth over 20 years to test the effects of
 environmental heterogeneity, nutrient enrichment, and potentially
 interactive effects of global change drivers (nutrient enrichment and a
 drought manipulation) on the phenology of a highly dominant prairie grass
 (Andropogon gerardii). We recorded the timing of major developmental
 stages of A. gerardii in plots containing four soil heterogeneity
 treatments (control, soil depth heterogeneity, nutrient/depth
 heterogeneity, and nutrient/precipitation heterogeneity). We found that
 the boot, first spikelet, and emerged spikelet stages of A. gerardii
 occurred earlier in treatments with greater heterogeneity of soil
 nitrogen, and this effect was driven by the accelerative effect of
 nitrogen enrichment on phenology. Reduced precipitation increased the
 flowering length of A. gerardii, but did not otherwise affect
 developmental phenology. There were no interactive effects among any soil
 resource treatments on phenology. These results advance our understanding
 of the relationship between plant phenology and global change drivers,
 which is important for understanding and predicting the timing of plant
 resource use and the provision of resources to higher trophic levels by
 plants under varying levels of resource availability.
description: # Nitrogen enrichment drives accelerative effect of soil heterogeneity on
 the flowering phenology of a dominant grass
 [https://doi.org/10.5061/dryad.rn8pk0pn7](https://doi.org/10.5061/dryad.rn8pk0pn7) ## Description of the data and file structure ### Files and variables **DATA:** Data are provided in one file (Krause et al 2024.xlsx) corresponding to the long-term experiment designated as the “Prairie Restoration Heterogeneity Plots” located at the Konza Prairie Long Term Ecological Research site in Manhattan, KS USA. Data collected in 2021 on phenology of *Andropogon gerardii*, nitrogen availability, soil moisture, and light availability are located in four tabs (pages) within the Excel file. Missing data are represented by values of “NA” (not available) and “null” (not applicable). Data correspond to an experiment in which 6-m x 8-m plots (n = 16 plots) were assigned to four soil heterogeneity treatments according to a randomized complete block design (n = 4 blocks). Within each block, plots were randomly assigned to one of four heterogeneity treatments: soil depth heterogeneity, nutrient/depth heterogeneity, nutrient/precipitation heterogeneity, or control treatment. All plots were further divided into twelve 2-m x 2-m subplots, each containing two 0.5-m x 0.5-m permanent sampling quadrats. Plots assigned to the soil depth heterogeneity treatment contained alternating 2-m x 6-m strips of deep and shallow soil (3 subplots/strip). Plots assigned to the nutrient/depth heterogeneity treatment contained 2-m x 8-m strips of reduced nitrogen, ambient nitrogen, and enriched nitrogen soil (4 subplots/strip) assigned perpendicular to 2-m x 6-m strips of deep and shallow soil (3 subplots/strip). Plots assigned to the nutrient/precipitation heterogeneity treatment consisted of 4-m x 6-m strips of ambient PPT and reduced PPT (6 subplots/strip) assigned to half of plots, perpendicular to the 2-m x 8-m strips of reduced nitrogen, ambient nitrogen, and enriched nitrogen soil (4 subplots/strip). **TAB: Phenology** DETAILS: These data pertain to Figures 2, 3, 4, and 5 Phenology life stage observations of *A. gerardii* were conducted weekly during the growing season of 2021 from May through November. Start date (Julian day) was the date of the first observation of each life stage within two 0.25-m2 permanent sampling quadrats in each 2-m x 2-m subplot (*n* = 24 per plot). Four stages of perennial grass phenology defined by Moore et al. (1991) were used to categorize *A. gerardii* phenology: boot (flowering structure begins to develop, marking the start of reproduction), first spikelet (first full emergence of flowering structure), emerged spikelet (all flowering structures fully emerged), anthesis (anther emergence), and senescence. Column description | COL | LABEL | DESCRIPTION | | :-- | :--------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | A | Heterogeneity | There were four plot-level heterogeneity treatments: nutrient/depth heterogeneity (=Maximum), soil depth heterogeneity (=Soil Depth), nutrient/precipitation heterogeneity (=Nutrient), and control (=Control). | | B | Nutrient | There were three subplot-level nitrogen treatments: Enriched N, Control, and Reduced N. | | C | Soil depth | There were two subplot-level soil depth treatments: shallow and deep. | | D | Precipitation | There were two subplot-level precipitation treatments: ambient PPT and reduced PPT. | | E | Block | The experiment contained 4 blocks. | | F | Plot | The experiment contained 16 plots. | | G | Subplot | Each plot contained 12 subplots. | | H | Quadrat | Each subplot was divided into two replicates (a and b). | | I | First Leaf | First Julian date observation of a leaf | | J | Elongation | First Julian date observation of elongation of leaf | | K | Boot | First Julian date observation of boot development | | L | First spikelet | First Julian date observation of full emergence of a flowering structure. | | M | Emerged spikelet | First Julian date observation of emergence of all flowering structures for an individual. | | N | Anthesis | First Julian date observation of anthesis | | O | Senescence | First Julian date observation of senescence. | **TAB: Nitrogen** DETAILS: These data pertain to Table S1 Relative availability of nitrate (NO3-N) was quantified using buried ion-exchange resins in 2021. Resin bags were constructed of nylon and contained 5 g of strongly basic anion exchange resins. Two resin bags were buried in the surface 10 cm of each subplot in May and retrieved in October. Nitrate passively collected on resins throughout the growing season. Nitrate was extracted from resin bags by shaking each bag in 75 mL of 2 mol/L KCl. Solutions were filtered through 0.4-μm polycarbonate membranes. Resin-collected NO3-N was determined on an OI Flow Solution IV autoanalyzer (OI Analytical, College Station, TX). Resin-collected NO3-N units are μg/bag. | COL | LABEL | DESCRIPTION | | :-- | :------------ | :---------------------------------------------------------------------------------------------------------- | | A | Heterogeneity | Four plot-level heterogeneity treatments. | | B | Nutrient | Three subplot-level soil nitrogen treatments were enriched N, ambient N, and reduced N. | | C | Soil depth | Two subplot-level soil depth treatments were shallow and deep. | | D | Precipitation | Two subplot-level precipitation treatments were ambient PPT and reduced PPT. | | E | Block | The experiment contained 4 blocks. | | F | Plot | The experiment contained 16 plots. | | G | Subplot | Each plot contained 12 subplots. | | I | Resin\_NO3 | Resin collected nitrate over the growing season (μg/bag). Values represent the average of two bags/subplot. | **TAB: GSM** DETAILS: These data pertain to Figure S1 Gravimetric soil moisture (GSM) was measured in nutrient/precipitation heterogeneity treatments every 2-3 weeks following rainout shelter installation (May 2021). In each plot, soil cores of 2-cm diameter and 20-cm were taken in two subplots with an identical treatment combination. The two soil cores were homogenized through a 4 mm sieve. A 20-g sample of soil was weighed, dried at 105°C for at least 48 hours, and reweighed. | COL | LABEL | DESCRIPTION | | :-- | :------------------ | :-------------------------------------------------------------------------------------------------------------------- | | A | Block | The experiment contained 4 blocks. | | B | Plot | The experiment contained 16 plots. | | C | Subplot combination | Sampled and homogenized subplots noted as “subplot.subplot.” | | D | Precipitation | Subplot-level precipitation (PPT) treatments were AMBIENT (ambient precipitation) and RAINOUT (reduced precipitation) | | E | Date | Date of soil collection (YYMMDD). | | F | AVG GSM | Mean gravimetric soil moisture content (%). | **TAB: Percent cover** DETAILS: These data pertain to Table S2 The maximum percent cover *of A. gerardii* was observed in two 0.5-m x 0.5-m permanent quadrats located in the center of each subplot during early September 2021. Maximum cover was then averaged across the two quadrats in each subplot for cover analysis. | COL | LABEL | DESCRIPTION | | :-- | :------------ | :-------------------------------------------------------------------------------------- | | A | Heterogeneity | Four plot-level heterogeneity treatments | | B | Nutrient | Three subplot-level soil nitrogen treatments were enriched N, ambient N, and reduced N. | | C | Soil depth | Two subplot-level soil depth treatments were shallow and deep. | | D | Precipitation | Two subplot-level precipitation treatments were ambient PPT and reduced PPT. | | E | Block | The experiment contained 4 blocks. | | F | Plot | The experiment contained 16 plots. | | G | Subplot | Each plot contained 12 subplots. | | I | Percent cover | Percent cover (%) of *Andropogon gerardii*. | **TAB:** **PAR** Photosynthetically active radiation (PAR, µmol/(m2s)) was measured in two 0.5-m x 0.5-m permanent quadrats located in the center of each subplot in June 2021 using a 50-cm ceptometer (Decagon Devices, Pullman, Washington, USA). Measurements were taken 2-m above rainout shelters and 2-m below rainout shelters, and at soil surface. Measurements represent an average of 5 values logged by the ceptometer. | COL | LABEL | DESCRIPTION | | :-- | :---------- | :------------------------------------------------------------------ | | A | Plot | The experiment contained 16 plots. | | B | Subplot | Each plot contained 12 subplots. | | C | Date | Date of data collection (YYMMDD). | | D | SW above RO | PAR collected above rainout shelter (µmol/(m2s), southwest quadrat. | | E | SW below RO | PAR collected below rainout shelter (µmol/(m2s), southwest quadrat. | | F | SW surface | PAR collected at soil surface (µmol/(m2s), southwest quadrat. | | G | NE above RO | PAR collected above rainout shelter (µmol/(m2s), northeast quadrat. | | H | NE below RO | PAR collected below rainout shelter (µmol/(m2s), northeast quadrat. | | I | NE surface | PAR collected at soil surface (µmol/(m2s), northeast quadrat. |