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).