Climatic Data and Edaphic Properties

For each plot, long-term high resolution (∼1 km²) climate data were extracted from the CHELSA database (Karger et al., 2017), including average monthly (T_i) and annual temperature (T_A), total monthly (P_i) and annual precipitation (P_A), and total precipitation during the driest quarter of the year (P_dq).

In the lab, composite soil samples (from the five pits) were air dried, crushed and 2 mm sieved, prior to determination of soil particle size by the hydrometer method (Bouyoucos, 1962). Soil pH and electrical conductivity were also estimated in a suspension of 1:1 water:soil (Doran et al., 1996), organic C determined by the Walkley–Black wet oxidation method (Nelson and Sommers, 1982), and total N by Kjeldahl wet-oxidation (Bremner and Mulvaney, 1982). Soil total P was determined by wet-acid digestion with HNO₃ and H₂O₂ (Jones et al., 1991).

The exchangeable cations K, Ca, and Mg were extracted with 1N ammonium acetate at pH 7 (Thomas, 1982), with K concentrations subsequently measured by Corning 410 flame photometer, and Ca and Mg, by Varian AA400 Plus atomic absorption. Carbonate content was determined using the Bernard method by measuring the evolved CO₂ after addition of HCl (Nelson, 1982). Maximum water holding capacity (WHC) was measured for each soil sample (Gardner, 1986): each soil sample was saturated with water in a cylinder, and WHC was calculated based on the weight of the water held in the sample vs. the sample dry mass (dried at 105°C for 24 h). By measuring WHC without taking into account stone and/or rock content, we refer to the intrinsic ability of mineral soils to hold water regulated mainly by pedogenetic factors that determines soil type and soil organic matter dynamics.