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Absorption and translocation of nitrogen in cucumber (Cucumis sativus L.) plants using the ¹⁵N tracer technique

TANEMURA, Ryota, KURASHIMA, Hiroshi, OHTAKE, Norikuni, SUEYOSHI, Kuni, OHYAMA, Takuji
Soil science and plant nutrition 2008 v.54 no.1 pp. 108-117
Cucumis sativus, absorption, crop yield, cucumbers, fruits, greenhouses, hydroponics, leaves, nitrates, nitrogen, nutrient solutions, roots, small fruits, stable isotopes, stems, tracer techniques
Cucumber (Cucumis sativus L.) plants were grown with hydroponics in a greenhouse and the absorption and translocation of nitrogen in the plants were investigated after the first fruit harvest using ¹⁵N-labeled nitrogen. The ¹⁵N-labeled nutrient solution, which contained 13 mmol L⁻¹ nitrate, was supplied for 7 days from first fruit harvest on 21 September, 2005. Following 7 days of ¹⁵N treatment, these plants received the same composition of non-labeled nitrogen for 16 days (chase period). Commercial-sized fruits, approximately 20 cm in length, were harvested every day. The whole plants were harvested three times at the beginning (21 September) and at the end (28 September) of the ¹⁵N treatment period, and at the end of the chase period on 14 October. The average nitrogen absorption rate was 196 mg plant⁻¹ per day during the ¹⁵N treatment period and 181 mg plant⁻¹ per day during the chase period. The labeled nitrogen was detected in the fruits within 1 day of the ¹⁵N treatment, and the percentage of nitrogen from labeled nitrogen in the harvested fruits increased up to approximately 50% at the end of the ¹⁵N treatment period. The percentage of labeled nitrogen in the fruits quickly decreased after changing from ¹⁵N solution to the non-labeled conditions during the chase period. At the end of the ¹⁵N treatment period on 28 September, the percentage distribution of labeled nitrogen was 46% in the leaves, 24% in the harvested fruits, 13% in the stems, 9% in the roots and 9% in the small fruits. After 16 days of chase period, the distribution of labeled nitrogen decreased in the leaves (33%), stems (6.5%), roots (3.6%) and small fruits (1%), but 56% of labeled nitrogen was distributed in the harvested fruits. Based on the result obtained, the nitrate absorbed from the medium is rapidly transported to young fruits as well as to leaves and stems. The nitrogen once assimilated or stored in the leaves, stems and roots is gradually redistributed to the fruits for supporting their rapid growth. To maximize the yield of cucumber fruits, it is necessary to supply sufficient levels of nitrogen continuously after the first harvest.