Abstract

Embothrium coccineum (Proteaceae) is a pioneer endemic species from temperate forests of southern South America. This species have a root adaptation to improve phosphorus (P) acquisition called cluster roots (CR), which have been reported frequently in species growing in nutritionally poor soil. These CR exude organic acids and phosphatases that allow solubilize and mineralize P, which represent a high carbon cost for the plant. It is unknown how this plant adjust the formation and functioning of CR with the age of seedling and if this depends on the soil on which it develop. The aim of this study was to evaluate the physiological adjustments of Embothrium coccineum growing in two soil with different nutritional characteristics in two stages of development. We conducted a pot experiment where seedlings were randomly assigned to growth in young volcanic or organic soil for a period of 8 or 24 months. We evaluated relative growth rate (RGR), biomass distribution, P and nitrogen (N) concentration in leaves, photosynthetic use efficiency of nutrients (N and P), carboxylates and phosphatase exudation by roots, and P availability (P-Olsen) in the rizhospheric and non-rhizospheric soil. Seedlings under one year-old had higher growth rates, greater nutrients concentration and photosynthetic use efficiency of N and P. In addition, they had higher phosphatase activity and carboxylates exudation rates by roots compared with older plants. Likewise, the plants growing on volcanic soil have higher cluster roots formation and higher root exudation (phosphatase and carboxylates), as reflected in the further increase of P-Olsen in the rhizosphere and non-rhizosphere soil. We conclude that E. coccineum adjusts its growth and functioning (rate of photosynthesis, efficient use of nutrients and root exudation) depending on their ontogenetic state and type of soil. In nutritionally poor soils, younger seedlings intensified their strategies for nutrient uptake (e.g. Root exudation) compared with older seedlings. Together, these features allow this species to stablish successfully in disturbed areas as young volcanic soils.