DOI: 10.5061/dryad.5mkkwh7g4
title: Data from: Rooting depth and specific leaf area modify the impact of experimental drought duration on temperate grassland species

description: Due to climate change, temperate grasslands are being exposed to
 increasingly severe droughts. Concurrently, land-use intensification is
 altering grasslands’ functional composition by promoting fast-growing,
 resource-acquisitive species with high specific leaf area (SLA). How SLA
 affects the ability of grassland species to resist and recover from
 increasingly severe droughts and if deep roots improve their drought
 performance remains unclear. To investigate this, we established a common
 garden field experiment including temperate grassland species with SLAs of
 17.9–39.3 mm2g-1 and maximal rooting depths of 16–252 cm. After 1.5 years,
 we simulated droughts for 0, 79, 134, 177 and 220 days. Drought effects on
 plant performance increased with drought length, reducing the survival of
 green tissue and annual biomass by up to ~50% across all 32 species
 considered. As plant-available water remained in deep soil layers by the
 end of all treatments, deep roots mitigated the negative effect of
 increasing drought length on productivity in the later stage of drought
 and favoured productivity after long drought. The low-to-high SLA trait
 gradient among the 16 graminoid species seemed to represent alternative
 survival strategies ranging from dehydration tolerance to dehydration
 avoidance, rather than drought sensitivity. Variable drought responses
 along the SLA gradient of forbs imply that multiple other traits are
 related to drought resistance across evolutionarily distant species.
 Synthesis: Our results suggest that deep roots are beneficial for
 temperate grassland species subjected to longer periods without rainfall
 when plant-available water is lacking in shallow soil layers but remaining
 in deep soil layers. In the face of increasing drought severity, we thus
 recommend (1) fostering deep-rooted species in intensive grasslands on
 deep, productive soil and (2) directing further studies towards
 identifying management practices that support deep rooting in semi-natural
 grasslands.
description: We selected 48 plant species from four functionally different
 seminatural or agricultural Swiss grasslands. In our common garden field
 experiment, these study species were allocated to four subplot types
 according to their prevalence in the reference grasslands. This should
 avoid that species chosen from the more productive reference grasslands
 would overgrow species from the less productive grasslands. In March 2021,
 which was 1.5 years after establishement, we covered the whole
 experimental site with a greenhouse plastic and simulated droughts for 0,
 79, 134, 177 and 220 days by omitting the regular watering of the
 respective plots.  We measured specific leaf area (SLA)
 on 12–14 relatively young but fully expanded leaves without obvious signs
 of herbivory, pathogens, or senescence of 6–12 adult individuals per
 species growing in control plots in May 2021. For species with both
 rosette and stem leaves, we measured stem leaves if available and we
 included all petioles and stipules into the measurements. We checked and
 completed our SLA measurements in June 2022. Further plant traits were
 compiled from literature and databases (see references in the README
 file) To measure plant performance under and after
 drought, we measured the biomass of each species in each subplot in three
 harvests in the year of drought and in one harvest in the post-drought
 season (file Biomass_data). We further recorded the abundance of each
 species in each subplot at the start of the experiment, at the start and
 the end of the respective drought treatment and in spring after the
 drought (Abundance_data). For these abundance records, we used a frame
 with 24 15 × 15 cm grid squares at fixed positions and recorded for each
 species in each subplot the grid squares in which the species
 rooted. Out of the 48 selected species, eleven species
 had only poorly established, for two species adequate maximal rooting
 depth values were not available, for two species we could not measure SLA
 adequately and one species had to be weeded when it started to overgrow
 other species in the subplot. Our analyses are thus based on the 32
 species with sla values in the file Species_traits_data
description: # Data from: Rooting depth and specific leaf area modify the impact of
 experimental drought duration on temperate grassland species ## File:
 Species\_traits\_data **Description:** Trait data of study species used in
 analyses. We measured specific leaf area (SLA) on 12--14 relatively young
 but fully expanded leaves without obvious signs of herbivory, pathogens,
 or senescence of 6--12 adult individuals per species growing in control
 plots in May 2021. For species with both rosette and stem leaves, we
 measured stem leaves if available and we included all petioles and
 stipules into the measurements. We checked and completed our SLA
 measurements in June 2022. Further plant traits were compiled from
 literature and databases (see references below). ### Variables * species:
 scientific species' name * species.abbr: abbreviation of scientific
 species' name * MRD: maximal rooting depth (cm) compiled from the TRY
 database (Kattge et al., 2011), Kutschera and Lichtenegger (1982,1992) and
 references cited therein, and from Fort et al. (2017) and Guerrero-Campo
 et al. (2006). For species with n/a no adequate MRD values were available
 * SLA: specific leaf area (mm2/g) measured on plants in control plots.
 Values are given for those species that were included in the analyses
 (others: n/a). * storage.org: presence (yes) or absence (no) of noticeable
 storage organs like root swellings, thick rhizomes, hypocotyl tubers,thick
 lignified main roots, or many thick non-lignified roots, compiled from
 Flora indicativa (Landolt & Bäumler, 2010) * veg.disp: category of
 vegetative dispersal compiled and summarized to long distance (longdist),
 short distance (shortdist) and no (none) vegetative dispersal organs from
 Flora indicativa (Landolt & Bäumler, 2010). * max.height: maximal
 height (cm) compiled from Flora Helvetica (Lauber et al., 2018). n/a: no
 adequate data available ### References Fort, F., Volaire, F., Guilioni,
 L., Barkaoui, K., Navas, M.‑L., & Roumet, C. (2017). Root traits are
 related to plant water‐use among rangeland Mediterranean species.
 Functional Ecology, 31(9), 1700--1709.
 [https://doi.org/10.1111/1365-2435.12888](https://doi.org/10.1111/1365-2435.12888) Guerrero-Campo, J., Palacio, S., Pérez-Rontomé, C., & Montserrat-Martí, G. (2006). Effect of root system morphology on root-sprouting and shoot-rooting abilities in 123 plant species from eroded lands in North-east Spain. Annals of Botany, 98(2), 439--447. [https://doi.org/10.1093/aob/mcl122](https://doi.org/10.1093/aob/mcl122) Kattge, J., Díaz, S., Lavorel, S., Prentice, I., Leadley, P., Bönisch, G., Garnier, E., Westoby, M., Reich, P., Wright, I., Cornelissen, J., Violle, C., Harrison, S., Van Bodegom, P., Reichstein, M., Enquist, B., Soudzilovskaia, N., Ackerly, D., Anand, M., . . . Wirth, C. (2011). TRY \-- a global database of plant traits. Global Change Biology, 17(9), 2905--2935. [https://doi.org/10.1111/j.1365-2486.2011.02451.x](https://doi.org/10.1111/j.1365-2486.2011.02451.x) Kutschera, L., Lichtenegger, E., & Sobotik, M. (1982). Wurzelatlas mitteleuropäischer Grünlandpflanzen Band 1: Monocotyledoneae: Gustav Fischer. Kutschera, L., Lichtenegger, E., & Sobotik, M. (1992). Wurzelatlas mitteleuropäischer Grünlandpflanzen: Gustav Fischer. Landolt, E., & Bäumler, B. (2010). Flora indicativa: Ökologische Zeigerwerte und biologische Kennzeichen zur Flora der Schweiz und der Alpen (2., völlig neu bearbeitete und erweiterte Auflage der Ökologischen Zeigerwerte zur Flora der Schweiz (1977)): Haupt. Lauber, K., Wagner, G., & Gygax, A. (2018). Flora Helvetica - Illustrierte Flora der Schweiz. 6., vollständig überarbeitete Auflage. ## File: Abundance\_data **Description:** Data from abundance records, used for analyses on abundance-based response variables. We recorded species' abundances in each subplot at the start of the experiment, at the start and the end of the respective drought treatment and in spring post drought. We used a frame with 24 contiguous 15 × 15 cm grid squares at fixed positions and recorded for each species in each subplot the grid squares in which the species rooted. Squares were only counted if plants of the respective species rooted therein had some green tissue left. Seedlings were not counted. ### Variables * plot: plot ID, plot was the unit of irrigation * treatment: category of drought length treatment. t0: control; t1: 79 days; t2: 134 days; t3: 177 days; t4; 220 days) * drought.length: length of simulated drought in days without precipitation or watering * ref.treat: reference treatment for the timing of a.startdrought and a.enddrought records, records in control plots were taken at the start and end of t1, t3 and t4 treatments * subplot.type: category of subplot type. Species were assigned to four different subplot types according to the reference grassland from which they were selected: steppe grassland, *Festucion valesiacae* (FES), semi-dry meadow, *Bromion erecti* (BRO), French ryegrass meadow, *Arrhenatherion elatioris* (ARR) and English ryegrass mowing pasture, *Cynosurion cristati* (CYN). This should avoid that species typically growing in more productive habitats overgrow species typically growing in less productive habitats. * subplot: subplot ID, each subplot measured 45 × 120cm. Each plot contained four subplots (one per subplot type) per plot * species.abbr: abbreviation of scientific species' name (see file "Species_traits_data" for full names) * func.group: functional group. Grass: graminoids; forb: non-leguminous forbs; legume: leguminous forbs) * a21: number of squares in which the species occurred at the start of experiment (integer) * date.a21: date of abundance record at the start of the experiment (year-month-day) * a.startdrought: number of squares in which the species occurred at the start of the drought treatment (integer) * date.startdrought: date of abundance record at the start of the drought treatment (year-month-day) * a.enddrought: number of squares in which the species occurred at the end of the drought treatment (integer) * date.enddrought: date of abundance record at the end of the drought treatment (year-month-day) * a22: number of squares in which the species occurred in spring post drought (integer) * date.22: date of abundance record in spring post drought (year-month-day) * gain.drought: number of squares in which the species did not occur at the start of the drought treatment but at the end of the drought treatment (integer) * loss.pd: number of squares in which the the species occurred at the end of the drought treatment but not anymore in spring post drought (integer) ## File: Biomass\_data **Description:** Data from biomass harvests, used for analyses of biomass-based response variables. The first three harvests took place in the year of the simulated droughts (2021), the fourth harvest in the post-drought season (2022). We cut the plants 4 cm above ground and dried them at 80° C for at least 24 h before weighing. We did not measure biomass in plots with t1 (79 days) drought treatment.  ### Variables * plot: plot ID, plot was the unit of irrigation. * treatment: category of drought length treatment. t0: control; t2: 134 days; t3: 177 days; t4; 220 days * drought.length: length of simulated drought in days without precipitation or watering * subplot.type: category of subplot type. Species were assigned to four different subplot types according to the reference grassland from which they were selected: steppe grassland, *Festucion valesiacae* (FES), semi-dry meadow, *Bromion erecti* (BRO), French ryegrass meadow, *Arrhenatherion elatioris* (ARR) and English ryegrass mowing pasture, *Cynosurion cristati* (CYN). This should avoid that species typically growing in more productive habitats overgrow species typically growing in less productive habitats. * subplot: subplot ID, each subplot measured 45 × 120cm. Each plot contained four subplots (one per subplot type) per plot * species.abbr: abbreviation of scientific species name (see file "Species_traits_data" for full names) * func.group: functional group. Grass: graminoids; forb: non-leguminous forbs; legume: leguminous forbs) * date.h1: date of first biomass harvest (year-month-day) * biomass.h1: biomass (g) per species and subplot in first harvest * date.h2: date of second biomass harvest (year-month-day) * biomass.h2: biomass (g) per species and subplot in second harvest * date.h3: date of third biomass harvest (year-month-day) * biomass.h3: biomass (g) per species and subplot in third harvest * date.h4: date of fourth biomass harvest (year-month-day) * biomass.h4: biomass (g) per species and subplot in fourth harvest (= post-drought biomass)