Seedling response of Nothofagus species to N and P: linking plant architecture to N/P ratio and resorption proficiency

Previous studies on mature forests of NW Argentinean Patagonia indicated that N is the main growth-limiting nutrient in most dominant tree species, while P limitation is uncommon, despite the soils’ volcanic origin. This pattern was inferred from leaf N/P ratios and resorption proficiencies, but has not been experimentally tested. We conducted a greenhouse trial with seedlings of two deciduous species of high timber quality, Nothofagus nervosa and N. obliqua, and soils characteristic of each species. Seedlings were fertilized with three levels of N (100, 200 and 400 mg kg−1 soil) with or without the concurrent application of a single P dose (60 mg kg−1 soil) during their second growing season. Response variables were morphological descriptors of shoot and root growth, N and P concentrations in green and senescent leaves and ectomycorrhizal infection. Both species were primarily limited by N: the addition of N resulted in higher shoot and root masses, an increased number of nodes, taller stems and greater basal and root diameters, while no effect of P was found. N/P ratios in green leaves and N and P resorption proficiencies indicate that with increased N availability P can become a secondary-limiting nutrient for N. nervosa. This was accompanied by the maintenance of ectomycorrhizal infection and mass allocation to roots in this species. The steep growth response of N. obliqua to N addition may signal a strong competitive capacity of this species when growing in soils of high N availability.Fil: Agüero, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Puntieri, Javier Guido. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Mazzarino, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Grosfeld, Javier Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Barroetaveña, Carolina. Centro de Investigación y Extensión Forestal Andino Patagónico; Argentina. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin