DOI: 10.5061/dryad.j9kd51c8h
title: High water use in desert plants exposed to extreme heat

description: Many plant water use models predict leaves maximize carbon assimilation
 while minimizing water loss via transpiration. Alternate scenarios may
 occur at high temperature, including heat avoidance, where leaves increase
 water loss to evaporatively cool regardless of carbon uptake; or heat
 failure, where leaves non-adaptively lose water also regardless of carbon
 uptake. We hypothesized that these alternative scenarios are common in
 species exposed to hot environments, with heat avoidance more common in
 species with high construction-cost leaves. Diurnal measurements of leaf
 gas exchange and temperature for 11 Sonoran Desert species revealed 37% of
 these species increased transpiration in the absence of increased carbon
 uptake. High leaf mass per area partially predicted this behavior
 (r2=0.39). These data are consistent with heat avoidance and heat failure,
 but failure is less likely given the ecological dominance of the focal
 species. These behaviors are not yet captured in any extant plant water
 use model.  
description: Field measurements occurred in 2018 between 4 June and 6 July in
 natural habitat at the Desert Botanical Garden (DBG) in Phoenix, Arizona,
 USA (33.46° N, 111.94° W, elevation 330 m). DBG is located in the northern
 Sonoran Desert and is characterized by hot and dry summers (June mean
 maximum Tair = 44 °C; average relative humidity (RH) = 18%), with mean
 annual precipitation (MAP) totaling 191 mm yr<sup>-1</sup>,
 35% of which falls during the summer monsoon. We
 selected 11 common Sonoran Desert woody plant species (three individuals
 per species = 33 plants). Selection was based on diversity of leaf and
 canopy architecture. Selected individuals were similar in size within
 species, fully exposed to sunlight, and occurred on similar terrain. All
 species were C3 with no known CAM expression, in order to focus on species
 that do not carry out nighttime gas exchange. Species
 measured and collected: <em>Chilopsis linearis</em>
 (Cav.); <em>Dodonaea viscosa</em> (L.)
 Jacq.; <em>Encelia farinosa</em> A. Gray ex
 Torr.; <em>Larrea tridentata</em> (DC.)
 Coville; <em>Olneya tesota</em> A. Gray.; <em>Populus
 fremontii</em> S. Watson; <em>Prosopis velutina</em>
 (Wooton) Sarg.; <em>Quercus turbinella</em>
 Greene; <em>Rhus ovata</em> S. Watson; <em>Simmondsia
 chinensis</em> (Link) C.K. Schneid.; <em>Vauquelinia
 californica</em> (Torr.) Sarg. Data collected:
 leaf gas exchange (net photosynthesis, transpiration and stomatal
 conductance); leaf traits (leaf area, leaf mass (dry and fresh)); leaf
 hydraulic traits (predawn and midday leaf water potential); microclimate
 (air temperature, relative humidity, vapor pressure deficit, wind speed);
 leaf temperature; soil temperature and moisture. Data
 processing was conducted using R software and manually using Microsoft
 Office Excel.
description: Each data file has a respective metadata file describing the data
 collected, units, and how sampling and collection occurred. Metadata files
 explained missing values (i.e., NA) when available. Data are uploaded as
 raw, processed, and/or filtered. Data are uploaded as
 *.csv (one data file, one metadata file per dataset) and as *.xlsx (one
 single file with a tab for data and another for metadata per
 dataset).