Experimental design and soil collection
Soils used in this study were collected from the 'Scrape Site' at
the Jornada Experimental Range (JER)/Jornada Basin Long-Term
Ecological Research site, New Mexico, USA. The Scrape Site was
first cleared of vegetation and the A and B Horizon in 1995 by
Brad Musick according to his specifications. Kris Havstad of USDA
Jornada Experimental Range may know more details. What is left is
a soil crust that is uniformly abrading down through wind erosion.
The scraping occurred on a 100 meter radius semi-circle. There are
three monitoring stations (East, Middle, West) in the semi-circle
of the Scrape Site. The West site is the windward site, the East
site is the leeward site, and the middle site is halfway between
the other two.
Soil analyses
Soils were classified according to the USDA guidelines. The
texture was determined by the hydrometer method. Soil pH and
electrical conductivity (EC) were measured in 1:1 soil to water
suspension (volume to volume; deionized water). Exchangeable
cations, including K+, Na+, Ca2+, and Mg2+ were analyzed in
ammonium acetate solution buffered to pH 8.5 using an inductively
coupled plasma optical emission spectrometry (ICP-OES, iCAP7200,
Thermo-Fisher, Freemont, CA, USA). Soil NO3− was extracted with 2
M KCl and analyzed by reduction to nitrite (NO2−) via cadmium
reduction. Soil PO43− was extracted using 0.5 M NaHCO3 adjusted to
pH 8.5. Both NO3− and PO43− were measured with a continuous flow
analyzer (San++, Skalar CFA, Skalar Analytical BV, Breda, the
Netherlands). Cation exchange capacity (CEC) was estimated as the
sum of exchangeable K+, Na+, Ca2+, and Mg2+. Exchangeable sodium
percentage (ESP) was calculated as ESP (%) = (exchangeable
Na+/CEC) × 100. Soil total C and total N were measured with a
C&N analyzer (LECO TruSpec, LECO Corporation, St. Joseph, MI,
USA). Mean values for a given soil variable are based on n = 10
replicates. To generate soil water retention curve for each soil
type, air-dried soil samples were sieved through 2 mm mesh and
rewetted with deionized water to create a range of water contents
(ranging from low [air-dried] to saturated in 0.025 g g−1
intervals; n = 6 per soil water content) per Campbell et
al. (2007). Water potentials of these soil samples were then
determined with a dewpoint water potential meter (WP4, Decagon,
Pullman, WA, USA). Following water potential measurements, soil
samples were oven-dried at 105oC for 24 h and weighed to derive
gravimetric water contents.
Pot trials
Pot trials were conducted in a greenhouse on the University of
Arizona campus in Tucson, AZ, USA. Small plastic pots (8 cm width
× 8 cm length × 6 cm height) were filled with either non-winnowed
or winnowed soil (n = 10 per species per soil type for a total of
120 pots). Pots had holes on bottoms to allow drainage of excess
water. Ten seeds per species were sown ~1 cm below the soil
surface in each pot for all species. Soils were brought to field
water capacity on the day of sowing and moistened with the same
amount of water daily thereafter. Seed germination, defined as
cotyledon emergence, was recorded daily. The experiment ceased
when zero cotyledon emergence was recorded in all pots for five
consecutive days. Two separate trials of the seedling growth
experiment were carried out: one in 2018 (04 March – 04 April, 31
days) and the other in 2019 (01 January – 17 March, 76 days). The
greenhouse received full sun exposure and contained no
supplemental lighting. The daytime temperature maximum was set at
32 degrees C and the nighttime minimum was 24 degrees C, which is
a favorable temperature range for the germination and growth of
the species in our experiment. During each experimental trial,
plants were grown in 26.5 cm tall × 3.15 cm diameter
"Cone-tainers" (Stuewe and Sons, Inc., Corvallis, OR,
USA). Pots (n = 12 per species per soil type for a total of 144
pots) had a 7.5 cm base layer of mineral wool (to prevent soil
from falling through drainage holes) overlain by 14 cm of play
sand. The sandy base layer was then topped (upper 5 cm) with
either non-winnowed or winnowed soil. Pots were spatially
randomized on the greenhouse bench. The pots were brought to field
capacity on the day of sowing and kept moist by adding the same
amount of water per pot daily thereafter. At the end of the
experiment, plant height and number of leaves were recorded.
Aboveground material was separated into leaf and stem categories
(for shrubs) and soils were gently washed away from roots. Plant
materials were oven-dried at 65oC for 48 h and weighed.
Please refer to Niu et al. (2021) for other details regarding
materials and methods.
References
Campbell GS, Smith DM, Teare BL (2007) Application of a dew point
method to obtain the soil water characteristic. In: Schanz T (ed)
Experimental unsaturated soil mechanics. Springer, Heidelberg, pp
71–75.
Niu, F., Pierce, N. A., Archer, S. R., & Okin, G. S. (2021).
Germination and early establishment of dryland grasses and shrubs
on intact and wind-eroded soils under greenhouse conditions. Plant
and Soil, 1-16.