In situ measurements of carbon and nitrogen distribution and composition, photochemical efficiency and stable isotope ratios in Araucaria angustifolia

Araucaria angustifolia (Bertol.) Kuntze is an indigenous conifer restricted to the southern region of South America. In this on-site field study, we provide a detailed description of the nitrogen compounds and sugars allocated to the different plant compartments in tall adult trees, young trees about 2-3 m tall and small seedlings at its northernmost occurrence in the mountains of Itatiaia (20 degrees 25'S; 44 degrees 50'W; 2,000 m a.s.l.), SE Brazil. We determined C and N contents, soluble sugars, soluble non-protein N-compounds and delta(15)N-signatures in leaves, roots, wood of stems, xylem- and phloem- sap. We also measured chlorophyll a fluorescence of photosystem II and carbon isotope discrimination reflecting photosynthetic activity and water-use efficiency. The high C and N concentrations in fine roots suggest that they are important reservoirs of N and C. Most nitrogen taken up from the soil was metabolised in the roots. The only inorganic nitrogen form detectable in the xylem sap was a small amount of ammonium. Glutamine was the dominant transport form of nitrogen in the xylem, while glutamate and the amides glutamine and asparagine were the most abundant soluble N compounds in the phloem. Total soluble non-protein N and sugar concentrations were significantly higher in the phloem of adult trees. In this particular site, A. angustifolia was apparently not exposed to water stress, as indicated by the high values of carbon isotope discrimination. The three developmental stages were clearly separated in terms of photosynthetic performance. Indeed, effective quantum yield of photosystem II increased from seedlings to adult trees under ambient irradiance.