Effects of temperature and nitrogen sources on growth and nitrogen assimilation of Curcuma alismatifolia Gagnep.

The effects of different temperatures (30/24 o C and 30/18 o C day/night temperatures) and N sources; nitrate (NO3 - ), ammonium (NH4 + ), mixed-N source (50 NO3 - :50 NH4 + ) in the nutrient solution on growth and N assimilation of Curcuma alismatifolia was studied in a soil-less culture medium. Plant grew taller when grown under the 30/24oC treatment and flower quality in terms of stalk length, size of inflorescence and number of bracts declined at low night temperatures. The highest nitrogen concentration (mg plant -1 ) in leaves was obtained when plants were supplied with NO3 - as the nitrogen source. Most nitrogen assimilation occurred in leaves at 30/24 o C, and in fibrous roots at 30/18 o C. There were positive linear relationships between the NO3 - content and NR activity in leaves, when plants were grown under both 30/24 o C (R 2 = 0.99) and 30/18 o C (R 2 = 0.96) treatments. The total amino acid concentration in NH4 + -fed plants was significantly higher than that of NO3 - - fed plants. Glutamic acid (Glu) was recognized as a major form of accumulated N in old rhizomes, particularly in plants supplied with NO3 - N at 30/18 o C, while asparagine (Asn) and aspartic acid (Asp) were the major form of the accumulated N in fibrous roots when plants were cultivated with low night temperature (30/18 o C).