Do rice roots enhance or reduce the nitrogen loss through the nitrification-denitrification
processes?
K. Kakuda1, Y. Ohashi2, H. Ando2, T. Nozoe1
1 International Rice Research Institute, DAPO Box7777, Metro Manila, Philippines.
2 Yamagata University, Tsuruoka, 997-0013, Japan.
Paddy rice has unique characteristics to survive in submerged conditions.
Development of Lysigenous aerencyma, which is widely found in aquatic plants,
is one of adaptive functions for anaerobic conditions. The plants that have
lysigenous aerencyma provide oxygen for the roots and oxidize some toxic
ions near the roots. In addition, ammonium nitrogen (N) that is stable form
of N in anaerobic soils is also oxidized, and then changed into nitrate N
near the roots. Thus, a certain amount of N is lost from agricultural ecosystem
through the following denitrification process in the vicinity to the roots,
though N is one of essential nutrients for growth of plants. However, it
is considered that a part of nitrate N that is produced near the root would
be absorbed by plants. N absorption by rice plants would play an important
role in suppression of N loss through the nitrification-denitrification processes
in the rhizosphere. Objective of this study is to evaluate the amount of
absorbed nitrate N produced in the vicinity to the roots. A pot experiment
was conducted in the greenhouse of Yamagata University, Japan. At the panicle
formation stage, a solution of 15-N labeled ammonium sulfate was injected
with a syringe at a soil depth of 50mm. The rate of applied N was 20kg ha-1.
The plant was collected x, y and z days after N injection. Nitrate N in the
plant was extracted by ethanol soon after plant collection. A certain amount
of nitrate N was detected in the extraction from rice plants after N injection,
though the soil was submerged through the experiment. The amount of ammonium
N that was extracted from rice plants was larger than that of nitrate N.←まだ、分析してないからわからないです。
These results suggest that rice plants absorbed nitrate N produced around
the rhizosphere, though ammonium N was main form of N absorbed by plants.
It is considered that absorption of ammonium N and nitrate N by rice plants
play an important roles in the suppression of N loss through the nitrification-denitrification
processed in the vicinity to the roots.
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