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Native forests in southern South America are constantly subjected to natural disasters such as volcanic eruptions. Soil affected by volcanic ash contain large amounts of total P but low P availability, as this element is strongly adsorbed to soil colloids (i.e. allophane). This lack of available P is one of the main limitations to plant growth. In this context, it is necessary an in-deep study of plant species that have developed some root physiological strategies for P acquisition. An example of this is the formation of cluster roots by Proteaceae species. Recently, information has been reported that aids to our understanding of the functioning of Proteaceae species growing in volcanic soils. The aim of this review is to discuss the ecophysiological role of Proteaceae species growing in young volcanic soils, with a special emphasis on Embothrium coccineum, a pioneer species of extremely disturbed environments. In summary, we reveal here that E. coccineum has several features that make it suitable for recovering degraded soils in south-central Chile. Some of these characteristics include its ability to survive and successfully establish in poor soils due to its specialized roots adaptation and its ability to shed its leaves under stressful conditions. According to recent evidence, E. coccineum has relatively low foliar nutrient resorption leaving at least half of the nutrients in its senescent leaves; this, in turn, promotes nutrient cycling via mineralization of its leaves. Finally, we conclude that the cluster roots of E. coccineum promote P solubilization and mineralization in the rhizosphere soil allowing for increased P availability for the plant itself and potentially also for neighbouring species.

This paper reviews the literature related to total and organic P (Po) levels present in both agricultural and forest soils from southern Chile. Different reports have demonstrated the high contents of total P (Pt) found in agricultural soils (1,000-3,000 mg kg-1) even in unfertilized soils. In most soils Po represents more than 50% of Pt, mainly as inositol penta- and hexaphosphates linked to Fe and/or Al. Lipid-P has been found in very small quantities suggesting very fast cycling. When phosphate fertilizers are applied to these soils, the bulk of P is accumulated as macromolecular-P complexes closely associated with soil organic matter. Close relationships have been found between organic C and Po and between Po and P associated with humic acids (HA-P). When applying Hedley's chemical fractionation procedure to these soils some significant P fractions or pools of high lability are obtained suggesting a potential plant availability of some forms of accumulated P, which can be manipulated by agricultural management. On the other hand, Pt in forest soils has been found in smaller quantities than in agricultural soils but Po also represents more than 50% of total P. The higher levels of labile P found in forest soils in comparison to agricultural ones together to higher C/Po ratios are suggesting a faster P cycling in forest ecosystems Se realizó una revisión de la literatura relacionada con los niveles de P encontrados en suelos agrícolas y forestales del sur de Chile. Diferentes reportes señalan el alto contenido de P total (Pt) en suelos agrícolas (1.000-3.000 mg kg-1) incluyendo suelos no fertilizados. En la mayor parte de los suelos el P orgánico (Po) constituye más del 50%, asociado muy íntimamente a la materia orgánica, principalmente a ácidos húmicos. Los inositol penta- y hexafosfatos asociados a Fe y Al constituyen la mayor parte de este tipo de P. El P lipídico constituye tan sólo pequeñas cantidades sugiriendo una rápido ciclado. La acumulación del P en los suelos producto de la fertilización se produce mayoritariamente a través de la formación de complejos macromoleculares con la materia orgánica. Cuando se aplica a estos suelos el fraccionamiento químico de Hedley se encuentran fracciones de diferente labilidad, lo que sugiere que un adecuado manejo de estos suelos puede inducir a un aumento en la disponibilidad de P. Los suelos forestales, en cambio, poseen menor cantidad de P aunque el Po también supera el 50% del Pt. Los mayores contenidos de formas lábiles de este elemento y una relación C/Po mayor señalan un ciclado más rápido del P en estos ecosistemas boscosos