Soil P availability along a catena located at the Sierra de Gata Mountains, Western Central Spain Marı ´a-Bele ´n Turrio ´n a, * , Knut Schneider b , Juan F. Gallardo b a Area of Soil Science and Soil Chemistry, E.T.S.I.I.A.A., University of Valladolid, Palencia 34004, Spain b Consejo Superior de Investigaciones Cientı ´ficas, Apt. 257, Salamanca 37071, Spain Received 22 August 2007; received in revised form 20 January 2008; accepted 23 January 2008 Abstract The main objective of this study was to know the soil P availability in Quercus pyrenaica (deciduous oak) forests at the ‘‘Sierra de Gata’’ Mountains (Central Western Spain) and determine the factors controlling the availability of P in these soils. Twelve different oak stands along a rainfall gradient were selected, differentiating underlying geological materials: granites and schist-greywackes. Samples from selected soil horizons were taken and the available soil P was determined using an anion exchange membrane (P AEM ). P retention capacity (P RC ) was used as a rapid measure of soil P adsorption. P mineralization rate and acid phosphatase activity (APA) were determined in samples of the epipedons. Sites developed over schist-greywacke materials showed significantly lower contents of P AEM than sites over granites. Soil P RC was related positively to the contents of organically complexed Al + Fe and negatively to P AEM contents, confirming that metal–organic complexes play an important role in the solubility and availability of soil P. The APA did not show any direct relationship neither with the net P mineralization rate nor with P AEM , but did with the soil organic carbon (SOC) content. P mineralization did not only depend on the biochemical mineralization, but also on the biological mineralization of SOC by heterotrophic micro-organisms, which activity is favoured by the SOC content. # 2008 Elsevier B.V. All rights reserved. Keywords: Forest soils; Available soil P; P soil adsorption; P mineralization; Acid phosphatase activity 1. Introduction P limitations of forest growth are usually associated rather with forest ecosystems of old Tropical land surfaces than with those of temperate zones (Herbert et al., 2003), which grow mainly on relatively recent soils due to the lower intensity of weathering and the impact of Pleistocene glaciations in higher latitudes; according to the model of Walker and Syers (1976), with the intensification of soil formation a gradual shift in the nutrient limitation for biomass production is usually occurring, moving from N to other pedogenic nutrients, such as P. Although the forests of Quercus pyrenaica in the ‘‘Sierra de Gata’’ Mountains (Western Central Spain) belong to the temperate deciduous forest type of medium latitudes, no glaciation took place in this area and land surface, therefore, had not been subjected to the drastic rejuvenation or changes and of many zones from the northern countries. Climatic changes during the Holocene have altered the direction of soil formation; as an example, the geological parent material of soils shows signs of Tropical paleo- weathering in great extensions of the Western Iberian Peninsula (Molina et al., 1987; Molina et al., 1990). The presence of Al-rich clay minerals (as kaolinite and gibbsite) in soils of the ‘‘Sierra de Gata’’ Mountains points out an influence of that paleo-weathering (Gallardo et al., 1980; Gallardo and Gonza ´lez, 2004). Consequently, many soils component formed on these substrates may be considered inherited from past Geological times and, because of that, intermediate between old residual Tropical (paleo-soils) and temperate forest soils. This fact may explain the possible P limitations of the forests of this area (Schneider et al., 2001) in spite of the relatively high contents in soil organic matter (SOM), in contrast to the generalised global tendency that N limitation occurs typically in the younger surfaces of temperate latitudes. Therefore, that situation could be similar www.elsevier.com/locate/foreco Available online at www.sciencedirect.com Forest Ecology and Management 255 (2008) 3254–3262 * Corresponding author. Tel.: +34 979 108331; fax: +34 979 108301. E-mail addresses: bturrion@agro.uva.es (M.-B. Turrio ´n), jgallard@usal.es (J.F. Gallardo). 0378-1127/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2008.01.076