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Algal nitrogen fixation in Californian streams: diel cycles and nocturnal fixation
Author(s) -
HORNE ALEXANDER J.
Publication year - 1975
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1975.tb00149.x
Subject(s) - diel vertical migration , nostoc , nitrogenase , dry weight , nitrogen fixation , zoology , biology , botany , fixation (population genetics) , nitrogen , ecology , cyanobacteria , chemistry , biochemistry , bacteria , genetics , organic chemistry , gene
Summary Thirty‐six hour diurnal studies of Ng‐fixation by Nostoc in a rocky‐bedded stream were carried out during the peak of the seasonal cycle of growth on clear and cloudy days in 1971 and 1972. On both occasions an unexpected pattern of N 2 ‐fixation occurred with maximum fixation rates in the light but also in the dark portion of the day, with lowest fixation periods in the early evening. I postulate that competition for reductant between nitrogenase and other processes, especially photorespiration, controls this unusual diel cycle rather than variations in the intracellular N‐pool. N 2 ‐fixation rates on a cloudless May day in 1971 ranged from 0.2 to 4.8 nmoles C 2 H 4 cm −2 h −1 and from 0.3 to 3.3 nmoles C 2 H 4 mg −1 h −1 dry weight of Nostoc , depending on time of day and favourableness of site. On the same site on a cloudy, rainy May day in 1972 fixation ranged from 0.5 to 3.1 nmoles C 2 H 4 mg −1 h −1 dry weight, and from 1 to 4.5 nmoles C2H4 mg −1 h −1 ash‐free dry weight of Nostoc . Since Nostoc is most abundant in unshaded areas, and since one‐third of each day's nitrogen i s fixed in the dark, future studies should take dark fixation into account.