INFLUENCE OF NITROGEN FORMS ON THE GROWTH AND NITROGEN METABOLISM OF BROMELIADS

Abstract

Bromeliads are good material for studying plant nutrition because of their ability to inhabit a great variety of ecosystems. The aim of this study was to evaluate and compare the effect of the form of nitrogen (N) on growth, tissue chlorophyll and free ammonium content, and the free amino acid profile between a terrestrial bromeliad (Ananas comosus) and an epiphytic one (Vriesea gigantea). Both bromeliads were grown in vitro either with (NH4)2SO4 or urea as the N source, containing 0, 1, 5, 10, 20, and 50 mM of N. Both forms of N stimulated the growth of A. comosus up to 10 mM N and V. gigantea up to 5 mM N. However, ammonium inhibited the growth of V. gigantea in a N concentration higher than 5 mM. The chlorophyll content increased up to 20 and 5 mM N in A. comosus and V. gigantea, respectively, diminishing afterward. The total free amino acid level rose substantially in both bromeliads in 50 mM N, mainly as ammonium; in 10 mM N only V. gigantea presented an increase of the total amino acid level in both N forms. Both bromeliads mainly accumulated Asn (up to 80% of the total of free amino acid in 50 mM N). Unexpectedly, V. gigantea grown in 10 mM N as urea presented a higher level of Asn, Ser, Glu, and Arg, and when cultivated in 50 mM N as urea, a higher level of Ala, Asp, Glu, and Gln, in comparison to ammonium. In summary, we presented evidence that the terrestrial bromeliad A. comosus showed a preference for inorganic N in a relatively higher concentration, and the epiphytic one, V. gigantea, preferred organic N at relatively lower levels.