Ecological and Biogeochemical Interactions Constrain Planktonic Nitrogen Fixation in Estuaries |
| |
Authors: | Roxanne Marino Francis Chan Robert W Howarth Michael Pace Gene E Likens |
| |
Institution: | (1) Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA, US;(2) Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA, US;(3) Department of Zoology, Oregon State University, Corvallis, Oregon 97331, USA; and, US;(4) Institute of Ecosystem Studies, Millbrook, New York 12545, USA, US |
| |
Abstract: | Many types of ecosystems have little or no N2 fixation even when nitrogen (N) is strongly limiting to primary production. Estuaries generally fit this pattern. In contrast
to lakes, where blooms of N2-fixing cyanobacteria are often sufficient to alleviate N deficits relative to phosphorus (P) availability, planktonic N2 fixation is unimportant in most N-limited estuaries. Heterocystic cyanobacteria capable of N2 fixation are seldom observed in estuaries where the salinity exceeds 8–10 ppt, and blooms have never been reported in such
estuaries in North America. However, we provided conditions in estuarine mesocosms (salinity over 27 ppt) that allowed heterocystic
cyanobacteria to grow and fix N2 when zooplankton populations were kept low. Grazing by macrozooplankton at population densities encountered in estuaries
strongly suppressed cyanobacterial populations and N2 fixation. The cyanobacteria grew more slowly than observed in fresh waters, at least in part due to the inhibitory effect
of sulfate (SO4
2−), and this slow rate of growth increased their vulnerability to grazing. We conclude that interactions between physiological
(bottom–up) factors that slow the growth rate of cyanobacteria and ecological (top–down) factors such as grazing are likely
to be important regulators excluding planktonic N2 fixation from most Temperate Zone estuaries.
Received 26 April 2002; Accepted 12 July 2002. |
| |
Keywords: | : nitrogen fixation estuaries eutrophication nitrogen limitation grazing heterocystic cyanobacteria |
本文献已被 SpringerLink 等数据库收录! |
|