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VARIATION IN INTERNAL δ 15 N AND δ 13 C DISTRIBUTIONS AND THEIR BULK VALUES IN THE BROWN MACROALGA PADINA AUSTRALIS GROWING IN SUBTROPICAL OLIGOTROPHIC WATERS 1
Author(s) -
Umezawa Yu,
Miyajima Toshihiro,
Tanaka Yasuaki,
Koike Isao,
Hayashibara Takeshi
Publication year - 2007
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.2007.00347.x
Subject(s) - nitrogen , nitrate , biology , environmental chemistry , zoology , ecology , chemistry , organic chemistry
The utility of δ 15 N measurements in Padina australis Hauck as a probe for its external nitrogen (N) sources was tested by monitoring the bulk values of chemical components [δ 15 N, δ 13 C, and N and carbon (C) contents] and their internal distributions during a 12 d incubation in a controlled environment. Under the saturated conditions of isotopically heavier nitrate than that of original algal tissue, the bulk δ 15 N in P. australis was enriched, but less than what was predicted from a simple mixing model, signaling possible isotopic discrimination during N assimilation and subsequent N efflux from the cells. The enhanced N content (%), which occurred simultaneously with this δ 15 N shift, was a useful signal indicating this phenomenon. Bulk δ 15 N was enriched, especially around the meristem, in tissues growing under conditions of higher irradiance and temperature, probably due in part to dissolved organic nitrogen (DON) excretion. The δ 13 C enhancement in bulk algal tissues, also associated with high photosynthetic activity, may be an additional signal indicating this unbalanced internal δ 15 N distribution. However, in summer and winter environmental conditions with periodic nitrate supplies simulating typical fringing reef waters, the difference in measured algal bulk δ 15 N from theoretical predictions was within ±1.0‰. This difference is very small compared with the variation in δ 15 N in possible N sources in coastal areas. In the field, therefore, δ 15 N in Padina can be used effectively to trace N sources in both space and time after determining algal N content and δ 13 C to determine whether large alterations occur in algal δ 15 N.