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Contribution of atmospheric nitrate to stream‐water nitrate in Japanese coniferous forests revealed by the oxygen isotope ratio of nitrate
Author(s) -
Tobari Y.,
Koba K.,
Fukushima K.,
Tokuchi N.,
Ohte N.,
Tateno R.,
Toyoda S.,
Yoshioka T.,
Yoshida N.
Publication year - 2010
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.4498
Subject(s) - nitrate , ecosystem , chemistry , environmental chemistry , nitrogen , forest ecology , environmental science , hydrology (agriculture) , ecology , geotechnical engineering , organic chemistry , engineering , biology
Evaluation of the openness of the nitrogen (N) cycle in forest ecosystems is important in efforts to improve forest management because the N supply often limits primary production. The use of the oxygen isotope ratio ( δ 18 O) of nitrate is a promising approach to determine how effectively atmospheric nitrate can be retained in a forest ecosystem. We investigated the δ 18 O of nitrate in stream water in order to estimate the contribution of atmospheric NO 3 −in stream‐water NO 3 −( f atm ) from 26 watersheds with different stand ages (1–87 years) in Japan. The stream‐water nitrate concentrations were high in young forests whereas, in contrast, old forests discharged low‐nitrate stream water. These results implied a low f atm and a closed N cycle in older forests. However, the δ 18 O values of nitrate in stream water revealed that f atm values were higher in older forests than in younger forests. These results indicated that even in old forests, where the discharged N loss was small, atmospheric nitrate was not retained effectively. The steep slopes of the studied watersheds (>40°) which hinder the capturing of atmospheric nitrate by plants and microbes might be responsible for the inefficient utilization of atmospheric nitrate. Moreover, the unprocessed fraction of atmospheric nitrate in the stream‐water nitrate in the forest ( f unprocessed ) was high in the young forest (78%), although f unprocessed was stable and low for other forests (5–13%). This high f unprocessed of the young forest indicated that the young forest retained neither atmospheric NO 3 −nor soil NO 3 −effectively, engendering high stream‐water NO 3 −concentrations. Copyright © 2010 John Wiley & Sons, Ltd.