DOI: 10.5061/dryad.vdncjsxxk
title: Intraspecific trait changes in response to drought lead to trait convergence between- but not within species

description: Drought is expected to increase in future climate scenarios. Although
 responses to drought of individual functional traits are relatively
 well-known, simultaneous changes across multiple traits in response to
 water scarcity remain poorly understood despite its importance to
 understand alternative strategies to resist drought. We grew 52 herbaceous
 species in monocultures under drought and control treatments and
 characterized the functional space using seven measured above- and
 belowground traits: plant height, leaf area, specific leaf area, leaf dry
 matter content, specific root length, average root diameter, and root dry
 matter content. Then, we estimated how each species occupied this space
 and the amount of functional space occupied in both treatments using trait
 probability density functions. We also estimated intraspecific trait
 variability (ITV) for each species as the dissimilarity in trait values
 between the individuals of each treatment. We then mapped drought
 resistance and ITV in the functional space using generalized additive
 models. The response of species to drought strongly depended on their
 traits, with species that invested more in root tissues and conserved
 small size being both more resistant to drought and having higher ITV. We
 also observed a significant trend of trait displacement towards less
 conservative strategies. However, these changes depended strongly on the
 trait values of species in the control treatment, with species with
 different traits having opposing responses to drought. These contrasting
 responses resulted in lower trait variability in the species pool in
 drought compared to control conditions. Our results suggest strong trait
 filtering acting on conservative species as well as the existence of an
 optimal part in the functional space to which species converge under
 drought. Our results show that changes in species trait-space occupancy
 are key to understand plant strategies to withstand drought, highlighting
 the importance of individual variation in response to environmental
 changes, and suggest that community-wide functional diversity and biomass
 productivity could decrease in a drier future. Knowing these shifts will
 help to anticipate changes in ecosystem functioning facing climate change.
description: Seeds of 52 species of herbaceous plants typical from European
 grassland ecosystems were obtained from a commercial supplier (Planta
 naturalis). When species germinated in Petri dishes the seedlings were
 then transplanted to plastic pots (11 x 11 x 12 cm height, 1L volume).
 Pots were filled with a mixture of a potting substrate (Biolan Murumuld)
 and sand. Pots were randomly placed in the greenhouse of the University of
 Tartu, Estonia. Then, we established monocultures with seven individuals
 of a single species per pot which were grown under well-watered
 conditions. One month after transplanting the seedlings to the pots, a
 drought treatment was applied to half of the pots (five pots per
 species). The experiment was harvested in late July 2020, when the first
 individuals started flowering, after month-long drought treatment. Plant
 traits related to drought responses and resource use strategies were
 selected and measured for each species following established
 protocols. These included seven above- and belowground traits: Vegetative
 plant height (H, cm), Leaf Area (LA, mm<sup>2</sup>), Specific
 Leaf Area (SLA, mm<sup>2</sup>
 mg<sup>-1</sup>), Leaf Dry Matter Content (LDMC, mg
 g<sup>-1</sup>), Specific Root Length (SRL, cm
 g<sup>-1</sup>), Average root Diameter (AvgD, mm), Root Dry
 Matter Content (RDMC, mg g-1). Before harvesting, we measured the plant
 height and collected one leaf per individual for three individuals per
 pot. Afterward, we collected the aboveground biomass and belowground
 biomass of all the individuals in each pot. Due to the difficulty in
 untangling the roots of the different individuals in a pot, root traits
 were estimated at the pot level. Roots were washed and a sample of finest
 roots (10-50mg) was collected. Leaves and fine roots were scanned at
 300dpi and 600dpi, respectively, using an Epson perfection 3200 Photo
 scanner for leaves and Epson V700 Photo scanner for fine roots. After
 scanning, leaves and roots were oven-dried at 60°C for 72h. AvgD and root
 length were determined using WinRHIZO Pro 2015 (Regent Instruments Inc.,
 Canada), and leaf area with ImageJ software. We averaged all traits values
 at the species level, attaining a single value for each trait in each
 treatment. The total aboveground biomass and total belowground biomass of
 each pot were oven-dried at 60°C for 72h and weighed.
description: The complete dataset is in the file.