Nitrogen nutrition of bromeliads

Abstract

Epiphytic bromeliads have no contact with the pedosphere, so they need to withdraw their nutrients from the atmosphere as well as from the host tree and animal debris, while terrestrial bromeliads, as Ananas comosus, generally depend on the soil as the main nutrient source. The aim of this study was to investigate and compare some aspects of the nitrogen metabolism of two bromeliads with different growth habits: Ananas comosus, a terrestrial bromeliad, and Vriesea gigantea, an epiphytic tank bromeliad. Nitrogen-starved plants were grown in vitro for 3, 7, 15, 30 and 60 days, either with 5 mM ammonium [(NH4)2SO4] or urea as the sole nitrogen source.When NH4+ was supplied to the plants, increase of chlorophyll content in A. comosus was faster than in V. gigantea. In the presence of urea, there was a significant increase in tissue free-NH4+ and total amino acids only for V. gigantea, after 15 days of the plants in culture. V. gigantea presented a higher level of total free amino acids than A. comosus when nitrogen was supplied to the plants. Asparagine was the main amino acid accumulated in both bromeliads when plants were transferred to the medium with nitrogen. When comparing the ratio of the main individual free amino acids between the bromeliads grown in NH4+ and urea, values (nmol g−1 FW) were 7.2 for asparagine, 5.3 for glutamate and 1.8 for aspartate in A. comosus, whereas the respective values in V. gigantea amounted to 2.3 for asparagine, 1.1 for glutamate and 0.7 for aspartate,. This indicates that the latter species assimilates urea more efficiently. The results prompted us to support the idea that V. gigantea, an epiphytic tank bromeliad, is better adapted to absorb and assimilate organic nitrogen, such as urea, whilst A. comosus, a terrestrial plant, is better adapted to inorganic nitrogen forms, such as ammonium.