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DISTRIBUTION AND PHYSIOLOGICAL DETERMINANTS OF BLUE‐GREEN ALGAL NITROGEN FIXATION ALONG A THERMOGRADIENT 1
Author(s) -
Wickstrom Conrad E.
Publication year - 1980
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.1529-8817.1980.tb03058.x
Subject(s) - nitrogenase , nitrogen fixation , biology , nitrogen , algae , botany , algal mat , cyanobacteria , microbial mat , zoology , chemistry , bacteria , organic chemistry , genetics
The capacity of thermal algal‐bacterial mats to fix nitrogen (N 2 ) was examined in an alkaline thermal stream, Rabbit Creek, of Yellowstone National Park. Nitrogenase activity and nitrogen‐fixation rates of mat cores placed in serum bottles and incubated in situ were estimated by the acetylene‐reduction technique. Active nitrogenase was not detected at 60 or 65 C in either the blue‐green algal or bacterial undermat components of the mats. Acetylene was reduced by all mats ≤55 C along the thermogradient; mean fixation estimates for the mats ranged from 7 to 5,028 nmoles N 2 fixed · mg Chl a −1 · hr −1 . Maximum fixation occurred at 35 C in the stream; statistical comparison of mean rates ordered the thermogradient mats according to estimated activities: 35 > 40 > 30 > 50 ≥ 55 ≥ 45 C. Mats (≤40 C) dominated by species of Calothrix accounted for ca. 97% of the total nitrogen fixation observed in the stream; the remaining activity was associated with mats containing Mastigocladus laminosus Cohn. Light intensity significantly affected fixation rates of the Calothrix mats which responded in a linear fashion from 9–100% full sunlight (ca. 1,900 μEin · m −2 · sec −1 ). Calothrix mats from 30 and 40 C had maximum nitrogenase activity at their growth temperature suggesting that nitrogen fixation along the thermogradient was optimally adapted to in situ temperatures.