Biomass accumulation, photochemical efficiency of photosystem II, nutrient contents and nitrate reductase activity in young rosewood plants (Aniba rosaeodora Ducke) submitted to different NO super(-) sub(3):NH super(+) sub(4) ratios

The rosewood (Aniba rosaeodora Ducke) is a native tree species of Amazon rainforest growing naturally in acidic forest soils with reduced redox potential. However, this species can also been found growing in forest gaps containing oxide soils. Variations in the forms of mineral nitrogen (NO super(-) sub(3) or NH super(+) sub(4)) may be predicted in these different edaphic conditions. Considering that possibility, an experiment was carried out to analyze the effects of different NO super(-) sub(3):NH super(+) sub(4) ratios on the growth performance, mineral composition, chloroplastid pigment contents, photochemical efficiency photosystem II (PSII), and nitrate redutase activity (RN, E.C.1.6.6.1) on A. rosaeodora seedlings. Nine-month-old seedlings were grown in pots with a washed sand capacity of 7.5 kg and submitted to different NO super(-) sub(3):NH super(+) sub(4) ratios (T sub(1) = 0:100%, T sub(2) = 25:75%, T sub(3) = 50:50%, T sub(4) = 75:25%, and T sub(5) = 100:0%). The lowest relative growth rate was observed when the NO super(-) sub(3):NH super(+) sub(4) ratio was equal to 0:100%. In general, high concentrations of NO super(-) sub(3) rather than NH super(+) sub(4) favored a greater nutrient accumulation in different parts of the plant. For the chloroplastid pigment, the highest Chl a, Chl b, Chl sub(tot), Chl a/b and Chl sub(tot)/C sub(x+c) contents were found in the treatment with 75:25% of NO super(-) sub(3):NH super(+) sub(4), and for Chl b and C sub(x+c) it was observed no difference. In addition, there was a higher photochemical efficiency of PSII (F sub(v)/F sub(m)) when high NO super(-) sub(3) concentrations were used. A linear and positive response for the nitrate reductase activity was recorded when the nitrate content increased on the culture substrate. Our results suggest that A. rosaeodora seedlings have a better growth performance when the NO super(-) sub(3) concentrations in the culture substrate were higher than the NH super(+) sub(4) concentrations.