Plant architecture of Paspalum vaginatum Schwartz modified by nitrate and ammonium nutrition

Paspalum vaginatum Schwartz plants were grown under greenhouse conditions i n a continuous-flow hydroponic culture, containing NO3- or NH4+ or NH4NO3 a s nitrogen source. After 30 days, the size of aerial biomass and root syste m decreased significantly when plants were supplied with NH4+ as exclusive nitrogen source. Compared to NO3- treatment, reducing and non-reducing suga rs were decreasing together with a significant increase in amino acids cont ent. NH4+-nutrition caused tillers to grow toward an orthogravitropic posit ion (average angle of 68 degrees with respect to the horizontal), and with NO3--nutrition, tillers tended to become diagravitropic (average angle of 2 3 degrees). With NH4NO3 all the parameters measured had values in between t hose of the other two sources. Thus, the morphologic differences among plan ts growing in NO3+ or NH4+ nutrition confirm the hypothesis that nitrogen s ource determines the growth habit of tillers in P. vaginatum by modulating the endogenous levels of reducing-non-reducing sugars.