Plant architecture of <i>Paspalum vaginatum</i> schwartz modified by nitrate and ammonium nutrition : Arquitetura de Paspalum vaginatum Schwartz modificada pela nutrição de nitrato e amônio

<i>Paspalum vaginatum</i> Schwartz plants were grown under greenhouse conditions in a continuous-flow hydroponic culture, containing NO-<SUB>3</SUB> or NH+<SUB>4</SUB> or NH<SUB>4</SUB>NO<SUB>3</SUB> as nitrogen source. After 30 days, the size of aerial biomass and root system decreased significantly when plants were supplied with NH+<SUB>4</SUB> as exclusive nitrogen source. Compared to NO-<SUB>3</SUB> treatment, reducing and non-reducing sugars were decreasing together with a significant increase in amino acids content. NH+<SUB>4</SUB>-nutrition caused tillers to grow toward an orthogravitropic position (average angle of 68° with respect to the horizontal), and with NO-<SUB>3</SUB>-nutrition, tillers tended to become diagravitropic (average angle of 23°). With NH<SUB>4</SUB>NO<SUB>3</SUB> all the parameters measured had values in between those of the other two sources. Thus, the morphologic differences among plants growing in NO-<SUB>3</SUB> or NH+<SUB>4</SUB> nutrition confirm the hypothesis that nitrogen source determines the growth habit of tillers in P. vaginatum by modulating the endogenous levels of reducing-non-reducing sugars. Facultad de Ciencias Naturales y Museo