DOI: 10.5061/dryad.q2bvq83j6
title: Data from: Plant functional types broadly describe water use strategies in the Caatinga, a seasonally dry tropical forest in northeast Brazil

description: In seasonally dry tropical forests, plant functional type can be
 classified as deciduous low wood density, deciduous high wood density, or
 evergreen high wood density species. While deciduousness is often
 associated with drought-avoidance and low wood density is often associated
 with tissue water storage, the degree to which these functional types may
 correspond to diverging and unique water use strategies has not been
 extensively tested.  We examined (1) tolerance to water stress,
 measured by pre-dawn and mid-day leaf water potential; (2) water use
 efficiency, measured via foliar δ13C; and (3) access to soil
 water, measured via stem water δ18O. We found that deciduous low
 wood density species maintain high leaf water potential and low water use
 efficiency. Deciduous high wood density species have lower leaf water
 potential and variable water use efficiency. Both groups rely on shallow
 soil water. Evergreen high wood density species
 have low leaf water potential, higher water use
 efficiency, and access alternative water sources. These findings indicate
 that deciduous low wood density species are drought avoiders, with a
 specialized strategy for storing root and stem water. Deciduous high wood
 density species are moderately drought tolerant, and evergreen high wood
 density species are the most drought tolerant group. 
 Synthesis. Our results broadly support the plant functional type
 framework as a way to understand water use strategies, but also highlight
 species-level differences. 
description: Leaf water potential was measured using a Scholander pressure
 chamber (1505D, PMS Instrument Company, Albany, OR) for leaves collected
 at pre-dawn (4:30–6:00 AM) and at mid-day (11:30–1:00 PM). The leaves were
 bagged and kept in cooler with ice, then immediately measured in-situ. 
 For foliar δ<sup>13</sup>C analysis, the additional leaves
 collected at pre-dawn  were oven-dried in the lab at 75°C to 80°C for at
 least 48 hours, then transported to the Stable Isotopes for Biosphere
 Science (SIBS) Laboratory at Texas A&M University, College
 Station, for grinding, weighing, and packing. These samples were analyzed
 for δ<sup>13</sup>C with an <em>Elemental
 Analyzer</em> (Costech Analytical Technologies, Valencia, CA)
 coupled to
 a <em>Thermo Scientific Delta V Isotope Ratio Mass
 Spectrometer (EA-IRMS; Thermo Fisher Scientific, Waltham,
 MA). </em>Soil and stem samples representing wet conditions were
 collected on April 10, 2018, and those representing dry conditions were
 collected on June 12, 2018. Samples for the evergreen species group were
 collected separately on September 19, 2018. The soil samples from seven
 pits at three integrated depths: 5–15 cm, 20–30 cm, and 40–50 cm. Soil and
 stem water was extracted via cryogenic vacuum distillation at
 100°C. Rainwater and throughfall samples were collected
 approximately bi-weekly from January 18, 2018 until June 9, 2018 (Fig. 1)
 in collectors wrapped with aluminum foil filled with a thin layer of
 paraffin oil to reduce evaporation (IAEA, 2014). Groundwater and surface
 water samples were also collected from the surrounding area. Water samples
 containing debris were filtered (0.2 μm) to remove particles. All water
 samples were analyzed using a High Temperature
 Conversion/Elemental Analyzer coupled to a Delta V Advantage Isotope Ratio
 Mass Spectrometer (TC/EA-IRMS). Please see corresponding publication for
 more details. 
description: Missing data is marked as NA. Data has been summarized (mean and
 standard deviation) by date and tree species or sample ID.