HR: 16:15h
AN: U52C-02    [PDF]
TI: The Use of Manipulations in Studies of Nitrogen and Carbon Cycling in Modern Microbial Mats
AU: * Bebout, B M
EM: Brad.M.Bebout@nasa.gov
AF: NASA Ames Research Center, Exobiology Branch Mail Stop 239-4, Moffett Field, CA 94035-1000 United States
AU: Carpenter, S
EM: scarpenter@mail.arc.nasa.gov
AF: NASA Ames Research Center, Exobiology Branch Mail Stop 239-4, Moffett Field, CA 94035-1000 United States
AU: Crumbliss, L L
EM: lcrumbliss@ucsd.edu
AF: University of California, Santa Cruz, Ocean Sciences Department 1156 High Street, Santa Cruz, CA 95064 United States
AU: Des Marais, D J
EM: David.J.DesMarais@nasa.gov
AF: NASA Ames Research Center, Exobiology Branch Mail Stop 239-4, Moffett Field, CA 94035-1000 United States
AU: Hoehler, T M
EM: Tori.M.Hoehler@nasa.gov
AF: NASA Ames Research Center, Exobiology Branch Mail Stop 239-4, Moffett Field, CA 94035-1000 United States
AU: Hogan, M E
EM: mhogan@mail.arc.nasa.gov
AF: University of California, Santa Cruz, Ocean Sciences Department 1156 High Street, Santa Cruz, CA 95064 United States
AU: Omoregie, E
EM: enomao@cats.ucsc.edu
AF: University of California, Santa Cruz, Ocean Sciences Department 1156 High Street, Santa Cruz, CA 95064 United States
AU: Thamdrup, B
EM: bot@biology.sdu.dk
AF: University of Southern Denmark, Institute of Biology Campusvej 55 5230 Odense M, Odense, Odense M Denmark
AU: Turk, K A
EM: kturk@mail.arc.nasa.gov
AF: University of California, Santa Cruz, Ocean Sciences Department 1156 High Street, Santa Cruz, CA 95064 United States
AU: Zehr, J P
EM: zehrj@emerald.ucsc.edu
AF: University of California, Santa Cruz, Ocean Sciences Department 1156 High Street, Santa Cruz, CA 95064 United States
AB: Modern microbial mats, laminated microbial communities analogous to the oldest known forms of benthic ecosystems on Earth, contain an invaluable biogeochemical and molecular record of processes and microorganisms thought to be important in their formation over geologic time. We are conducting manipulations of environmental conditions thought to be important in the ecology of microbial mats in order to better understand mat biogeochemical cycling. We present here the results of long-term (ca. one year) manipulations of nutrient and sulfate concentrations in water overlying mats kept in a greenhouse. As the element often limiting production in the marine environments, nitrogen takes on special significance in microbial mat ecology. Microbial mats are often the sites of high rates of N fixation (the energetically expensive conversion of atmospheric dinitrogen into a biologically useful form) and mats host an extremely diverse assemblage of nitrogen fixing microorganisms. Incubation of mats in the absence of nutrient additions resulted in the developments of higher rates of nitrogen fixation as the community of nitrogen fixing microorganisms responded to the shortage of nitrogen. Additions of phosphorus additionally stimulated nitrogen fixation whereas additions of combined nitrogen suppressed nitrogen fixation. We have also incubated modern microbial mats at the lower sulfate concentrations thought to be present in the Archean and early Proterozoic Eons. On the modern Earth, high concentrations of sulfate enable sulfate reducing microorganisms to out-compete methanogens for substrates, consequently dominating the degradation of organic carbon in the marine environment. However, very high rates of microbial methane production are implicated in generating the high atmospheric methane concentrations thought necessary to counteract the effects of a less luminous sun during the Archean and early Proterzoic. Lowered sulfate concentrations in our manipulations did result in lowered rates of sulfate reduction, and an increased (up to six fold higher) flux of methane from these mats. The quantitative importance of methanogenesis in carbon remineralization, even under low sulfate conditions, was, however, relatively small. The results of these experiments demonstrate the utility of environmental manipulations in examining biogeochemical cycling in the environments in which they evolved, namely complex communities of microorganisms.
DE: 0400 Biogeosciences
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 1615 Biogeochemical processes (4805)
DE: 8125 Evolution of the Earth
SC: U
MN: 2003 Fall Meeting