Effect of heating on mineral components of the soil organic horizon from a Spanish juniper (Juniperus thurifera L.) woodland

Spanish juniper (Juniperus thurifera L.) grows optimally on high (1000–1100 m) Iberian moorland (Central Spain), in the French Alps, and in the High Atlas mountains of Morocco, where it must withstand adverse climatic conditions. These plants are characterized by their great resistance to the droughts and cold winter spells of the Mediterranean basin. Nowadays, the species is in clear decline due to intensive grazing and its slow growth rate; juniper plants are also susceptible to fire damage due to the resin in their leaves. To avoid soil degradation, however, the conservation of this species is essential. This paper reports the effect of temperature on the mineralogical composition and the dynamics of the soluble cations and anions in the organic horizon of a soil under this type of plant cover. The mineral components of this horizon and of the leaves of J. thurifera were determined, and their transformations recorded when subjected to different temperatures in the laboratory. Whewellite, a mineral that turns into calcite at around 400 °C was detected by X-ray diffraction in both the organic horizon and the leaves. Boehmite, goethite, CT opal, manganese oxide (birnessite), potassium sulphate and mixed sulphates of potassium and ammonium were also found in both types of sample at 300 °C. Maximum mineralogical transformation occurred between 200 and 300 °C. The dynamics of the soluble cations and anions largely explains the presence of calcite, birnessite and sulphates. The tendency of soluble phosphate anions to disappear with increasing temperature would lead to the reduced leaching of P. Nitrates accumulated with increasing temperature, meaning their losses through leaching might increase.