Study site and plant species
The study site is located at the Río Mayo Experimental Field Station of
INTA (Instituto Nacional de Tecnología Agropecuaria) in South Central
Patagonia (45º24′11″S 70º17′37″W, 500 m a.s.l.). The historical mean
annual temperature (1982-2018) is 9.4°C, with a mean monthly temperature
in January of 15°C and in July of 2°C. The historical mean annual
precipitation (1982-2018) is 130 mm, with an annual range between 50 and
250 mm. Most precipitation occurs in the autumn and winter, while summer
precipitation events are isolated and unpredictable. Most of the
precipitation events are less than 5 mm (88% of the total), and 55% of
them are less than 1 mm (Cavallaro et al., 2020). Soils are coarse
textured (sandy), have a high gravel content and a calcareous layer at a
depth of 45-150 cm. Soil nitrogen content is low, around 0.05%
(Carbonell Silletta et al., 2022). Soil water content varies seasonally
in the shallowest layers down to 1 m depth, increasing from about 5 to
20% between May and September, while remaining relatively constant and
close to 10% throughout the year at higher depths (Pereyra et al.,
2017).
The study site corresponds to a grass-shrub steppe in the southern end
of the Western District of the Patagonian Province. The major land use
in the region is sheep grazing (Golluscio et al., 1998). The Patagonian
steppes are arid to semiarid ecosystems characterized by a low plant
species diversity and a low plant density, with a vegetation cover of 30
to 40% (Pereyra et al., 2017). The vegetation is distributed in patches
composed of shrubs and grasses on a bare soil matrix (Soriano et al.,
1994). The dominant shrub species in the study area are Azorella
prolifera (Cav.) G.M. Plunkett & A.N. Nicolas (ex Mulinum
spinosum ), Adesmia volckmannii Phil. and Senecio
filaginoides DC. Dominant grass species, which are C3, includePappostipa speciosa (Trin. & Rupr.) Romasch., Pappostipa
humilis (Cav.) Romasch. and Poa ligulari s Nees ex Steud (Table
1). The dominant life forms of the Patagonian steppe have root systems
that collectively explore the entire soil profile down to at least 2 m
depth (Bucci et al., 2011) (Table 1).