“Chemolithoautotrophy is the non-photosynthetic biological conversion of C1 molecules (usually CO2 or CH4) into organic matter."These authors studied the chemolithoautrophic community in the south-eastern Pacific ocean, at a long-term research position on the small continental shelf of Chile. At this position, the water is about 90m deep, and is part of one of the largest and most productive upwelling regions of the world, where productivity is extremely high. For about 70% of the year, surface winds drive upwelling that brings nutrients such as NO3- up to the photic zone, allowing massive planktonic productivity. Some of these plankton are non-photosynthetic prokaryotic autotrophs, using inorganic molecules such as NH4+, NO2-, and HS- as electron donors to drive the energy-intensive process of fixing inorganic carbon, chiefly CO2, as organic matter. These organisms require oxygen as an electron acceptor, thus they are all aerobic organisms and do not thrive in anaerobic environments. Assimilation of CO2 in the dark is the diagnostic signal of the presence of these organisms. Some chemolithoautrophs use CH4 in addition to or instead of CO2, but always under aerobic conditions; anaerobic methanotrophs are outside the scope of this study, and have not been identified in this system.
Nitrous oxide accumulates in these waters, indicative of greater production than consumption. These authors state that N2O reduction can only occur through a single identified pathway, that of total denitrification that takes NO3- or NO2- all the way to N2, and only under extremely limited O2 conditions; they cite Elkins et al. (1978) and Farías et al. (2009). Variation in space and time in dissolved N2O patterns do suggest some consumption is occurring, but in general production outweighs consumption.
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