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Intraspecific variation in surface water uptake in a perennial desert shrub

Citation

Zaiats, Andrii et al. (2020), Intraspecific variation in surface water uptake in a perennial desert shrub, Dryad, Dataset, https://doi.org/10.5061/dryad.pk0p2ngjm

Abstract

  1. Despite broad recognition that water is a major limiting factor in arid ecosystems, we lack an empirical understanding of how this resource is shared and distributed among neighboring plants. Intraspecific variability can further contribute to this variation via divergent life-history traits, including root architecture. We investigated these questions in the shrub Artemisia tridentata and hypothesized that the ability to access and utilize surface water varies among subspecies and cytotypes.
  2. We used an isotope tracer to quantify belowground zone of influence in A. tridentata, and tested if spatial neighborhood characteristics can alter plant water uptake. We introduced deuterium-enriched water to the soil in plant interspaces in a common-garden experiment and measured deuterium composition of plant stems. We then applied spatially-explicit models to test for differential water uptake by A. tridentata, including intermingled populations of three subspecies and two ploidy levels. 
  3. The results suggest that lateral root functioning in A. tridentata is associated with intraspecific identity and ploidy level. Subspecies adapted to habitats with deep soils generally had a smaller horizontal reach, and polyploid cytotypes were associated with greater water uptake compared to their diploid variants. We also found that plant crown volume was a weak predictor of water uptake, and that neighborhood crowding had no discernable effect on water uptake. 
  4. Intraspecific variation in lateral root functioning can lead to differential patterns of resource acquisition, an essential process in arid ecosystems in the contexts of changing climate and seasonal patterns of precipitation. Altogether, we found that lateral root development and activity is more strongly related to genetic variability within A. tridentata than to plant size. Our study highlights how intraspecific variation in life strategies is linked to mechanisms of resource acquisition.

Methods

Deuterium isotope ratios in plant stems

The experiment included the addition of high-concentration deuterium solution into the soil with subsequent sampling of plants around the injection point. In the dataset, the 'id' variable marks individual plants of big sagebrush (Artemisia tridentata) in the common garden. The 'subspecies' variable indicates the subspecies identity of A. tridentata, including A.t. tridentataA.t. vaseyanaA.t. wyomingensis, and 'ploidy' indicates the number of homologous sets of chromosomes. The 'size_m3' corresponds to the shrub crown volume in cubic meters, measured as three perpendicular dimensions of the crown (height, longest width, perpendicular width). The volume was calculated using a standard ellipsoid volume equation using the three measurements. The 'd_D_diff_permil' variable corresponds to the difference between post-tracer addition and pre-treatment deuterium concentration (=natural abundance) in plant stems. The measurement units are in [permil, ], where zero indicates no change (i.e., tracer uptake) in deuterium ratios between post- and pre-experiment. The common garden was divided into 14, 6 x 6 m meter square plots,  'subplots' variable, with one deuterium injection location in the center of each subplot. The 'D_dist_m' variable then shows the proximity of each plant to the nearest injection location (=within the same subplot). artr_deuterium_data_fe.csv

Plant water status

The data include pre-dawn and mid-day leaf water potentials, measured during the time of the experiment using a Scholander Pressure Chamber (see manuscript for details). The variables, including 'id', 'subspecies', and 'ploidy', correspond to the unique plant identifier, subspecies identity, and ploidy level respectively for each big sagebrush plant (Artemisia tridentata). The 'treatment' variable indicates the time of the day when the measurement was obtained. The pre-dawn measurements were obtained from between 3:30 am and 5:00 am, and the mid-day values from between 2:00 pm and 3:00 pm. The 'p_mpa' variable indicates leaf water potential in [MPa] units. artr_deuterium_water_pot_data_fe.csv

Usage Notes

The common garden is location in NRCS Orchard Range Site in south-eastern Idaho, USA (43° 19' 19"N, 115° 59' 49"W). The leaf water pontetial measurements were taken from a subsample of plants that were measured for deuterium isotope abundance.

Funding

NSF Idaho EPSCoR, Award: OIA‐1757324