Accumulation of carbon and nitrogen compounds in sweet potato plants grown under different nitrogen application rates

Abstract

Sweet potato (Ipomoea batatas L. var. Beniazuma) plants were grown in a cold region at 4 nitrogen application rates. Results are as follows.

1.	Total dry weight and tuberous root dry weight decreased at a high nitrogen application rate (30 g N m-2). The growth at 30 N was restricted from the early growth stage and the nitrogen content was higher at 30 N. As the plant architecture at 30 N did not show a large difference compared to the low nitrogen application rate, it is assumed that the carbon metabolism of sweet potato was disturbed by the high rate of nitrogen application at which level other field crops grew well, but not by mutual shading.
2.	Harvest index of dry weight and nitrogen for sweet potato ranged from 0.6 to 0.7, and 0.2 to 0.5, respectively. Thus, the distribution of nitrogen to tuberous roots was lower than that of carbon (dry weight). Therefore, sweet potato has an ability to attain a high potential productivity at low nitrogen application rates because a high photosynthetic rate can be maintained due to the high distribution ratio of nitrogen to leaves compared to potato or grain crops.
3.	Ratio of sporamine and β-amylase to total nitrogen in tuberous roots increased with growth until 105 d after transplanting, then decreased.
4.	Main amino acids consisted of alanine, aspartic acid, asparagine, and glutamic acid in leaves, asparagine in stems, asparagine and glutamic acid in tuberous roots.

Key Words:

• amino acids
• β-amylase
• carbon-nitrogen interaction
• source-sink interaction
• sporamine