| Summary: | Nothofagus antarctica (G. Forster) Oerst. (ñire) occupies a latitudinal gradient ranged from 36° 30´ to 56° 00’ S, and extends from sea level to 2,000 m a.s.l. It is the species with widest ecological amplitude in Nothofagus spp. from south-America covering in southern Patagonia (Argentina) 431,000 ha and growing mainly between the N. pumilio forests and steppe where water conditions are limiting. Productivity and different ecological issues of ñire forests have been previously assessed. However, specific studies related to the functional response to water stress of species are scarce. Therefore, the main subject of present study was to evaluate the functional response and growth of ñire seedlings under the interaction of water stress and two light conditions. Ten seedlings were grown during 6 months in a climatic chamber under a photoperiod 14/10 hours of light/darkness, a temperature range of 25ºC day / 20ºC night, and 65% relative humidity. One shoot on each seedling was shaded from the beginning of the experiment with a shading mesh (transmittance of 5 % of full light). The rest of plant received at the top 800 µmolm-2s-1 PPFD. After five months of well-watering conditions, half of seedlings were submitted to a water stress cycle by one additional month. By the end of experiment, diameter growth at the base of stem seedling was measured. In addition, different leaf functional parameters were recorded: specific leaf área (SLA), net photosynthesis (An), stomatal conductance to water vapor (gwv), and different parameters from building P-V curves: osmotic potential at maximum and zero turgor (Π100; Π0), relative water content at zero turgor (RWC0), maximum modulus of elasticity (Emax), and dry/fullhydrated weight ratio (DW/TW). Plant water status was recorded measuring predawn water potential (Ψpd). Light and water stress affected most leaf functional parameters with synergic to antagonistic impacts depending on a particular trait. EEA Santa Cruz Fil: Bahamonde, Héctor Alejandro. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Fil: Bahamonde, Héctor Alejandro. Universidad Nacional de la Patagonia Austral; Argentina. Fil: Sánchez-Gómez D. Instituto Nacional de Investigaciones y Tecnologías Agrarias y Alimentarias. Centro de Investigación Forestal (INIA-CIFOR); Chile. Fil: Gyenge Javier. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce. Agencia de Extensión Rural Tandil; Argentina. Fil: Gyenge Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina. Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Aranda, I. Instituto Nacional de Investigaciones y Tecnologías Agrarias y Alimentarias. Centro de Investigación Forestal (INIA-CIFOR); Chile.
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